Hip Pocket Builders' Forum

Indoor Free Flight Forum => F1D, F1M, F1L => Topic started by: Olbill on August 09, 2009, 03:40:08 PM



Title: VP Hubs - for the techies among us
Post by: Olbill on August 09, 2009, 03:40:08 PM
These pictures are all from 2004 and 2005 but represent several of the common and uncommon VP hubs in use.
From left to right:
Dezso Orsovai
Ivan Tregers
Lutz Schramm
Peter Kuttler
Kornechuk
Ron Green


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on August 09, 2009, 03:50:25 PM
More hubs.

Ukranian double spring hub (cm - not inches!)
Kevlar wound hub
Kevlar wound hub for 35cm
Tissue tube hub
Keller hub
Nick Aikman hub


Title: Re: VP Hubs - for the techies among us
Post by: MrTurtle on August 09, 2009, 09:10:39 PM
Steve Brown
?
Tom Sova
John Kagan
Doug Schaefer
Richmond's VD

Photos by Zaluska


Title: Re: VP Hubs - for the techies among us
Post by: FlyF1D on August 10, 2009, 12:39:53 AM
Tom Sova's 35cm hub (that's not a bagel, it's a Cheerio!)

Ray Harlan’s “inverted” VP features pass-through actuator arms and a boron reinforced hub


Title: Re: VP Hubs - for the techies among us
Post by: Sundance12 on August 10, 2009, 11:04:07 AM
Awsome examples of mechanics, thanks for posting those images, just amazing.

Sundance12


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on August 10, 2009, 01:09:05 PM
Here's one of my F1M VP. This is much heavier than the ones pictured before and is not suitable for F1D but it works very well - 2 World Records (one pending) and 2 wins at USIC. I have the greatest respect for people who can build a beautiful piece of functioning machinery at such a small size and weight. For the cavemen builders among us this picture shows that such a high level of cragtsmanship isn't totally necessary to make something that works.

Also here's an article I did a few years ago for building VP hubs suitable for Penny Plane and F1M. The hub pictured below is the next hub I built after doing the article. It's basically the same design but just built lighter.

http://www.indoornews.com/modules/articles/article.php?id=3 (http://www.indoornews.com/modules/articles/article.php?id=3)



Title: Re: VP Hubs - for the techies among us
Post by: mkirda on July 20, 2012, 09:43:26 AM
Just wondering if there was anything similar out there for VD mechanisms...

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on July 20, 2012, 10:41:29 AM
Mike
The case for VD's looks pretty strong for efficiency gains over VP's and I'm not one to discourage people from going for whatever advantage they see. That being said I know 3 top F1D fliers and a few other assorted brave individuals who have invested a lot of energy in VD's. As far as I know the current situation is unchanged from several years ago - Jim Richmond is the only person successfully using VD's in competition. Here's a really grainy jpeg of an old INAV drawing of Jim's mechanism.


Title: Re: VP Hubs - for the techies among us
Post by: Dave Andreski on July 20, 2012, 11:15:37 AM
Not sure if this will help but here goes...
From Model Builder, Sept., '85.
Dave Andreski


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on July 20, 2012, 04:25:54 PM
INAV 121 has an article by Jim Richmond with detailed drawings and pictures.  If you can't find it I'll figure out a way to post it here.

I would also echo what Bill said which is that while VD might be theoretically better, most people that try it go back to VP.  The only other person I know of that had some success was Rich Doig, and even he had a lot of problems with it.  I watched him spend hours trying to get his prop to work at the '96 world champs.


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on July 20, 2012, 04:44:21 PM
INAV 121 has an article by Jim Richmond with detailed drawings and pictures.  If you can't find it I'll figure out a way to post it here.

I would also echo what Bill said which is that while VD might be theoretically better, most people that try it go back to VP.  The only other person I know of that had some success was Rich Doig, and even he had a lot of problems with it.  I watched him spend hours trying to get his prop to work at the '96 world champs.

Hi Jake.
I have a Lulu reprint copy, thanks. If someone has a copy of Slobodan Midic's figures from INAV 123 that is legible, I'd appreciate a copy.
The Lulu reprint is illegible.
I also couldn't figure out the 7 degree angle - like where that was supposed to be in relation to the propeller center line.
Reading the reprint, I just found it interesting and wanted to understand it.
It wasn't until I held one of Brett's VP props that it clicked for me and I really understood the pictures.
I'm kind of at the same place with these VD mechanisms.

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on July 20, 2012, 04:53:20 PM
Speaking of Brett's VP prop, does anyone have pictures of his carbon prop?  I assume the 42 minute flight was done with it, but I haven't seen pictures. 


Title: Re: VP Hubs - for the techies among us
Post by: green-man on July 22, 2012, 02:23:01 AM
Here's a pic of Brett's model by Nick Ray, 'borrowed' from Facebook.

The type of carbon used is important - you can't just use any old stuff.

Also, 2 pics of Lutz's carbon prop from the 2010 F1D Belgrade Champs.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on July 23, 2012, 12:59:22 PM
Thanks for the pics.  I'm still working to get my regular VP props working well so these are a little bit off for me.  That said, I think this will probably be the next big thing in F1D.  What is different about the carbon he's using?


Title: Re: VP Hubs - for the techies among us
Post by: green-man on July 23, 2012, 01:23:31 PM
It has to be ultra-high modulus carbon which is stiffer than normal ;).


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on July 23, 2012, 03:05:18 PM
It has to be ultra-high modulus carbon which is stiffer than normal ;).

So where can one source this extra stiff carbon?
I am a long ways off from playing with carbon for outlines, but it seems to me the most difficult part of this hobby is often sourcing the proper materials.
I'd buy some just so I could play with it later...

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on July 23, 2012, 03:37:44 PM
I'd buy some just so I could play with it later...

This is exactly my thinking.  I've realized over the years that if I see something I like I should buy it now even if I don't plan to use it for a while.  So many things in the world of indoor have disappeared over the years.


Title: Re: VP Hubs - for the techies among us
Post by: green-man on July 23, 2012, 03:42:23 PM
I don't know Mike. I think Brett has tried several different types so you could ask him.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on July 23, 2012, 03:52:52 PM
I found some high modulus unidirectional fabric at the link below.  I'm guessing you could separate fibers to make your own tow for an outline, but I'm not sure if that's a good solution.  Perhaps someone can ask Brett what he's using.

http://www.cstsales.com/uni_carbon_fabric.html


Title: Re: VP Hubs - for the techies among us
Post by: green-man on July 23, 2012, 04:15:54 PM
Taking strands out of what looks like a Russian unidirectional cloth is the way that Lutz started with carbon. Lutz sent me a sample and it's very easy to seperate the strands into usable pieces. But I think? that Lutz, Brett and Ivan are now using strands taken directly from carbon tow.


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on July 23, 2012, 04:20:00 PM
Hexcel IM8,9 or 10 look to have the proper modulus. It appears that they come only in 12K tow, so it would be relatively difficult to separate versus 1K.
I'm still looking...

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: green-man on July 23, 2012, 05:11:17 PM
From an email to me from Ivan: -

"Lutz used HM roving M46J( Mitsubishi, Toray yarn). I tried it but it is problem to separate a very fine strand of those roving which I need for insert to gap of the form. The gap is very delicate, it start from 0,4 square to 0,15 square mm.
For my cf outlines I used HM roving Tenax UMS 40 which is good for separated a fine strands. Next time I want to use stronger roving Mitsubishi Dialead K 63712, or Granoc CN60 which have very small elongation and the fibre is thicker than Tenax or Toray fibres.
I use only the resins for aeroplane : Ciba geigy ( Vantico) 5052XB which have excellent mechanical properties.

The complete weight of my propellers is from 260 to 270mg."

Nick.



Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on July 23, 2012, 05:32:42 PM
Thanks for the info Nick.  I found a nice data sheet for the Mitsubishi Dialead K63712 material.  Now I need to figure out where I could buy something like this.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on July 24, 2012, 02:44:36 AM
Have the guys mentioned,

- what kind of fiber/resin -ratio they aim for / have achieved? The best laminates should have 50 to 70% fibers, but for prop outlines at reasonable weight this may produce too thin outlines. Larger dimension would mean stiffer outline (this is why balsa is so good stuff in indoor construction). Also,

- did they get to the final dimensions by laminating, or did they have to sand the laminate down?

I tried to make some carbon outlines in a silicone mold a few years ago, but failed miserably. The result was heavy and flimsy. Also, I would have needed to sand the outline down to weight, and I did not like the idea, but would rather develop a molding tecnique that would produce final outlines right out of the mold. After that unsuccessfull attemp I decided to stick to balsa and try to solve my other F1D building problems first... :-)

... talking of VP's, I attach a pic of my latest VP hub. Construction mostly pultruded carbon tubing. The blade attachement tubes are still paper, as I'm working on solid methods to make them of carbon (so that I could use deliberate amounts of glue to attach prop spars and still would be able to use acetone to solve the glue). The inner prop blade holding wire (that also doubles as actuator meeting the cross bar) makes a 90 degree angle to go into the main tubing, the latter has a machined slot in it. Had to buy a cross-feed table to go with my drill press to be able to drill those holes, 0.3mm diameter bit into a 0.3mm ID 0.7mm OD tubing was a bit hard to drill free-hand. The hub weights about 130mg; a bit too much but it is also much stiffer than balsa construction.


Title: Re: VP Hubs - for the techies among us
Post by: green-man on July 24, 2012, 02:53:54 AM
Morning Tapio.

I know that Lutz and Brett sand the outlines to produce tapered square sections but I think you'll have to ask the carbon prop users in Belgrade the other questions - carbon props are bound to be one of the hot topics of conversation.

Nick.


Title: Re: VP Hubs - for the techies among us
Post by: ljr8378 on October 04, 2012, 08:13:55 PM
Anyone know haw they get the kevlar wrapped so nicely?


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on October 04, 2012, 11:28:00 PM
Anyone know haw they get the kevlar wrapped so nicely?

A needle helps. I pull kevlar from tow, add a bit of thinned ambroid to it to make a thread, then glue, hold, knot. Mostly it is practice and just fiddling with it until you get it good enough. There must be a better way, I just haven't figured it out yet...

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: green-man on October 05, 2012, 02:53:56 AM
It really helps to have a weight on the free end of the kevlar - several grams of modelling clay or similar will do the trick. That way, the thread is always under tension and that helps to make nice tight hinges. I suspect that Ivan may have some sort of mechanical contraption to aid the process - he makes and sells a lot of hubs now.

Nick.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on October 05, 2012, 03:02:07 AM
Indeed. I have not actually ever managed to make any good kevlar hinges, but my efforts have improved when I have:

- made a jig that holds the hub body and the tissue tubes firmly in place, and frees my both hands to work the kevlar, and
- have pulled the kevlar quite tight. Much tighter than I initially thought. If the jig that holds the tissue tube is steel (same mandrel that it was turned on), it will support the tube, and if the hub body is balsa, the kevlar needs to crush it a bit (or at least almost) to be tight enough.

But you can take that with a grain of salt, I have never been happy with my kevlar hinges... :-(


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on October 05, 2012, 07:09:46 PM
he makes and sells a lot of hubs now.

Are purchased VP hubs legal in FAI competitions?  They really aren't hard to make so I'm not sure I understand why someone would buy one anyways.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on October 06, 2012, 01:00:16 AM
They are. I have always wondered why buying the single most important part of the model does not violate the BOM rule...


Title: Re: VP Hubs - for the techies among us
Post by: green-man on October 06, 2012, 03:16:38 AM
Not all flyers find VP hubs easy to make and some Juniors would find it impossible. I think it's relatively straightforward for most flyers to complete a hub that works but much more difficult to get it down to the necessary weight. A hub that weighs anything more than about 220 mg is probably too heavy and useless if you're trying to get down to a 1.2 g total. Ivan's hubs weigh around 80 mg so that's a considerable advantage. In addition, some flyers probably buy them thinking that Ivan's success may rub off on them ::)

Nick.


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on October 06, 2012, 11:23:02 AM
I've built many VP hubs recently.  Although I can build the parts, I find that assembling them is not easy.  I believe that building the VP hub is the number 1 barrier to entry for F1D.

At the same time, it doesn't seem to me that having a Treger VP hub is a ticket to high performance.  I'm pretty sure that the top 5 finishers use their own VP hubs.  Do any of you know which top 10 finishers this year used a bought VP hub?

These being the case -- 1.VP hub is a barrier to entry, 2. bought VP hub is not necessary for top performance -- means that the BOM rule for VP hub is detrimental for this event and should be relaxed.


Title: Re: VP Hubs - for the techies among us
Post by: leop on October 06, 2012, 01:45:03 PM
Nick, did you mean 120mg for the maximum weight of a useful F1D vp hub rather than 220mg?

Jake had a reasonable question about the legality of purchased F1D vp hubs.  Some at the 2012 Indoor F1D WC used purchased hubs.  But, has the use of purchased hubs ever been protested in an F1D competition, national or international?  Is there some ruling by the FAI that such purchased hubs do not violate the BOM rule?

Leo


Title: Re: VP Hubs - for the techies among us
Post by: green-man on October 06, 2012, 02:39:20 PM
AAAAAAAAAAAAAAAAAAAAAAAAAAARGH! Yes, I meant 120 mg (too much balsa dust affects the little grey cells).

Yes I agree, Jake's query is entirely reasonable and although bought hubs have been used for years, I'm not aware of any protests at major F1D comps regarding their use. If they are the same as the BMFA rules, the exact FAI rules state
Quote
The entrant must be the constructor of the model. The constructor may employ generally available building aids or small components in the production of their model but the airframe must be the competitor’s own work.
- Hmmmmmm that seems to imply that bought hubs should not be allowed. Anybody else see it differently?

Nick.



Title: Re: VP Hubs - for the techies among us
Post by: leop on October 06, 2012, 03:24:38 PM
The FAI's BOM rules reads as follows:

B.3.1 Competitor
         a)  Unless otherwised stated, the competitor named on the entry form must be the builder of the model aircraft entered.

There is no more detail given, unlike the quoted BMFA rule.  The AMA rule for US fliers in a somewhat more detailed:

6. Builder of Model: The CD shall make every reasonable effort to assure himself that each flier has completely “constructed‟ the model(s) he uses in competition, including the covering where used, with “constructed” to be interpreted as the action required to complete a model starting with no more prefabrication than the amount used in the average kit. Models which are completely prefabricated and require only a few minutes of unskilled effort for their completion shall be excluded from competition. In the case of rubber-powered models (excluding Indoor duration models), commercially available balsa, plastic, and hardwood propellers may be used. Materials and design may be obtained from any source, including kits. The builder-of-the-model rule applies to every AMA event unless specifically noted otherwise in the rules governing that event.


I am of the opinion that complete vp hubs are contrary to the BOM rules for both the AMA and the FAI.  However, the FAI rules apply for the F1D class in the US and any FAI rulings and interpretations apply.  Certainly if complete vp hubs may be purchased, why not preglued balsa tubes with boron applied  and spars with boron applied, etc.?

Leo


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on October 07, 2012, 10:48:54 AM
I wonder if you are heading down the rabbit hole here...
Want to grow your own balsa and lay your own mylar?
How about that forge for making the steel in the music wire?
Or making your own tissue and glue? How far do you want to go?

If VP is the biggest barrier to entry and they are available commercially, why disallow them?
If the builder does 95% of the model, but purchases the hub, seems to me that they built it.
The hub is just one part of the whole.

Others that feel differently - Lobby to change the rule to disallow purchased hubs. There must be a process to allow for rules changes in FAI. I'm pretty ambivalent myself.

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on October 07, 2012, 08:24:02 PM
All I know is if I was flying at the WC's and someone beat me with a purchased hub, I would be upset about it. 

Regarding construction, I don't think perception is reality.  They seem hard to build, but I can build several in a weekend with a few extremely simple jigs and fixtures.


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on October 07, 2012, 09:14:38 PM
All I know is if I was flying at the WC's and someone beat me with a purchased hub, I would be upset about it. 

Regarding construction, I don't think perception is reality.  They seem hard to build, but I can build several in a weekend with a few extremely simple jigs and fixtures.

Please share pics of the jigs and fixtures... I'd love to see what others are doing...

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on October 07, 2012, 10:09:30 PM
Most of what I use has been published by others at one time or another.  The only thing possibly unique about mine is how I drill the carbon yoke.  When I have a chance I'll take pictures of everything I use to make mine, but it's all pretty simple.  All you need is a drill press.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on October 08, 2012, 04:11:42 PM
I need to build some props this winter so I've decided to do a comprehensive VP build thread.  I'll take pictures of all the jigs and fixtures I use and outline the process step by step.  I'm certainly not the authority on VP props, but my mechanisms look nice, they're very consistent, and they're easy to build.  I'm essentially using the mechanism Steve Brown wrote about in the mid 90's with a few upgrades like a carbon fiber yoke and a top hat bend in the shaft.  I'm also using hypodermic tubing instead of aluminum bearings.

I don't use tube sockets so I don't know the weight of just the mechanism, but my last 19" prop weighed ~265mg finished.  I've identified places to save weight and I anticipate the next set of props will be about 250mg.  I'm also going to add low pitch adjustment on these new props.


Title: Re: VP Hubs - for the techies among us
Post by: ljr8378 on October 09, 2012, 01:37:49 PM
I look forward to your posts on the build of F1D VP props.  With Stan Chilton as my mentor, I built a couple of F1D models several (~8) years ago.  I have built both fixed pitch and VP props also using guidance from Stan and Steve Brown's articles. I will try and post a picture of my prop block/jig this evening.

I build the prop hub by cutting a length (~6 in) of 6 lb balsa that is the proper width (0.10 in) and thickness (0.068 in).  The using the excess material as a handle/hold I drill a prop shaft hole (~ 0.013 in).  I use a Dremel mounted in a drill press type holder to drill the prop shaft hole. I am not sure how accurate the hole is drilled in relation to the length and width of the hub (i.e. how perpendicular it is).  Do you have a jig or some other method for drilling the propshaft hole?

Thanks,

Lauren Rezac


Title: Re: VP Hubs - for the techies among us
Post by: ram on October 09, 2012, 03:03:40 PM
Jake,

Looking forward to following your VP Hub build.

Rey

PS:  is this you?


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on October 09, 2012, 06:21:30 PM
Where did you find that?  That is me, and I think that mini-stick was the first model I ever built.


Title: Re: VP Hubs - for the techies among us
Post by: ram on October 09, 2012, 07:22:56 PM
It's from Gitlow's indoor book.  Near the beginning.  I'm not home right now so I don't know exact page.

Rey


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on October 10, 2012, 01:13:44 AM
I was working for Lew when he published that book, but I didn't hang on to a copy of it.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on October 10, 2012, 02:12:32 AM
About hub construction; mine (pic in message #23) weights about 130mg, which is a bit too much. I could get rid of lots of pultruded carbon if I shortened the main cross bar. That part being a tube I could easily adapt similar prop hangers as those used by the Romanians and Ukrainians, a T-shaped piece of piano wire where the vertical part actuates pitch change, one cross bar (single wire) goes into the tube as hinge and the other (folded double) holds the spar or tissue tube.

What makes me wonder though is that the prop blade can then pivot back and forward if the piano wire bends. Will a 0.3mm wire be stiff enough to keep the blades from bending in an uncontrolled manner? A longer main bar would mean a stiffer hub.


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on October 10, 2012, 02:01:22 PM
.3 mm wire is thick.  It's stiffer than the prop spar, so it should be more than strong is enough.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on October 10, 2012, 02:06:42 PM
How about thinner wire? 0.25 for instance? Would save weight, but is that too flexible then? What size of wire is usually used for such hubs?


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on October 11, 2012, 02:02:14 AM
You don't need a lot of the wire inside the tube nor extended for the prop spar. 

I experimented with .25 mm wire, and I think it's strong enough.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on October 11, 2012, 02:35:54 AM
Oukey dokey, I'll have to try that.

There is one thing where the lenght of the wire inside the tube may matter: it will also be the hinge points against which the blade rotates (opening end of the tube and the very inwards tip of the wire. The shorter the distance between the two, the stronger the moments, and the more the hinges will "bind". Or, the less the friction, the smoother the action of the VP...


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on August 23, 2013, 01:09:03 AM
Inspired by the carbon hubs of Kang, Jake and Tom, I also built a new one. I am still a bit worried about the friction between two putruded carbon parts, so I thought of a way to replace one of the bearing surfaces with plastic. My older hub ( http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=2318.msg86479#msg86479 ) used piano wires inserted into grooves slotted onto the carbon tube, but these were wuite tedious to work. Yet I stuck to that solution, making the center part of the hub wider and hinging the blades onto a wider center. Unlike Kangs design, the center tube is just a muffle to insert carbon rods onto, and the hinges are the short pieces of plastic tube wrapped onto the blade roots. In addition, this construction omits the tissue tubes to attach the blades onto; the hinge tubes are solid, but if base pitch of the blade needs to be adjusted, the piano wire controlling the angle can be re-glued. For F1D hub I might make that of carbon rod and install permanently; if prop angle needs to be adjusted it can be dissolved from the stub spar and reglued.

I have not yet added lock rings to keep the blades in place, but they can be added if needed. The cross-arm on the shaft has holes in the ends, not slots, so those should also keep the blades in place. We'll see.

This prop is for F1M, it weight altogether 680mg. 100mg reduction from my previous prop. The blades are a bit lighter, but so is also the hub. I do not have a comparison weight to old hub, as the stub spars are nowe a part of the hub itself.

Ahh, for the scale, the adjustment screws are M2. I save the smaller ones for F1D... :-)


Title: Re: VP Hubs - for the techies among us
Post by: THB on August 23, 2013, 05:08:41 AM
Tidy work Tapio - I'm going to have a go at these soon. Magnifiers help - or are your eyes still good enough?
cheers
Tim


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on August 23, 2013, 09:47:23 AM
Thx.

They are good enough, I have build-in reading glasses: ~+3 diopters, so I can see sharply at close distances without my spectacles. But need those to see further away :-)



Title: Re: VP Hubs - for the techies among us
Post by: Maxout on August 23, 2013, 01:25:32 PM
Tapio,

 That looks nice and less difficult to build/maintain than your previous designs. Let us know how it works for you.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on August 23, 2013, 03:08:15 PM
Wilco. First session tomorrow! :-)


Title: Re: VP Hubs - for the techies among us
Post by: THB on August 27, 2013, 07:44:37 AM
First session tomorrow! :-)

Good luck Tapio. Your eyesight is better than mine I think. I found these in a local Red Cross charity shop. No really!
If glasses make you look smart (see Marilyn Monroe quotes from How to Marry a Millionaire) then these would make me irresistable, I reckon. Just ask my ex-wife...   8)


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on August 28, 2013, 01:32:14 AM
No luck past Saturday; for the summer time the electric keys to the gym had been deactivated, and the guy responsible for them had forgotten to activate them... But now they should work, so another attempt next Saturday....


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on August 31, 2013, 03:54:51 PM
Yes, it works. With a rather soft spring, and the IIFI contest on the way, I thought to try to set the prop up for low ceiling flying. My local gym is 7 meters (20 feet) high; I started with a quarter motor to get adjustments about right, then went to full motors. After a few trials and start-collisions to the wall (the gym is only 15 meters wide, so making the first turn within the gym is tought) managed to get one decent flight under my belt. Climbed to the ceiling, came half-way down, the climbed again to scrub the ceiling for two minutes. Overall time in the clock 13'44", but that lacks a few seconds, as I only started the clock after launch, and had to wiggle with the stopwatch on my mobile. Ah well, inofficial time anyway.

But yes, the adjustments were repeatable and predictable, and on the best flight the bump the ceiling (at top pitch) did not change flight pattern compared to the previous that did not bump. So it seems that the hinges are not binding.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 01, 2013, 12:47:03 PM
There was a question of my prop dimensions in FB. So I measured. Diameter 440mm. High pitch 1100 mm (at 145mm radius), low pitch 550mm. Changeover from 21g*cm to 17. Motor was 360mm long, took 1800 turns at 40 g*cm max torque, and model landed with 600 turns left.


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on September 01, 2013, 01:07:10 PM
Tapio, that's a really good flight time. Landing with that many turns indicates you could decrease the low pitch some more (55 cm seems a little high to me anyway) provided that extra ceiling bumping doesn't carry the risk of a snag.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 01, 2013, 02:54:06 PM
Yup, maybe open the spring up just a tiiny bit to let the model come down lower before the second climb starts, to have more room for the climb. But then again, the practice gym is really small, and for the fine-tuning I should fly in a place where the initial turn does not go from one wall to another...


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on September 01, 2013, 04:01:53 PM
Tapio,

 Soft springs really do put you in a position of having to resist the urge to do something unless you absolutely have to. With a little work, though, you can consistently get a model to descend within 5 ft of the floor before leveling out and climbing away. Either way, running low rpms on the second climb is hurting you if you're landing with so many turns...there's something to be said for just letting the model bounce away. If IIFI is in the usual place, ceiling bumping shouldn't be a problem, and using up those remaining turns would give you 14 minutes+. I only know of two people who have done that in Cat I.


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on September 01, 2013, 07:22:04 PM
Tapio,

 Soft springs really do put you in a position of having to resist the urge to do something unless you absolutely have to. With a little work, though, you can consistently get a model to descend within 5 ft of the floor before leveling out and climbing away. Either way, running low rpms on the second climb is hurting you if you're landing with so many turns...there's something to be said for just letting the model bounce away. If IIFI is in the usual place, ceiling bumping shouldn't be a problem, and using up those remaining turns would give you 14 minutes+. I only know of two people who have done that in Cat I.

And one of them is way behind the other one!


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 02, 2013, 12:47:53 AM
If IIFI is in the usual place, ceiling bumping shouldn't be a problem, and using up those remaining turns would give you 14 minutes+.

Or, bend me a little harder spring, so that the transition would start at the same torque, but end at lower, therefore making the second climb later/slower....


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 16, 2013, 05:55:53 AM
Another session two days ago. This time only managed 12'12" and 13'24". I had fixed the prop after previous session (asymmetry in the yoke made the pitch change uneven and caused some shakes. Replaced the yoke & shaft), now had to start adjusting anew. Also weather inside the hall was worse now, with model doing some "waterfalls" (wing and tail stall resulting in vertical loss of altitude) and therefore losing some precious height. I took a videoclip of the 12 minutes flight so that I can calculate prop RPM later (too hard to do in real time, but much easier from vid), which shows the turbulence in the hall, as well as the tight space during the first round (had to steer to avoid collision to sidewall. The video also shows nicely the flight pattern: quick climb to ceiling in less than 3 minutes, then descent to half height until 7; another climb to ceiling and then final descent. If anyone is interested to see that, I uploaded it to youtube (but will probably replace the clip with a better one if I improve my time :-) ... http://www.youtube.com/watch?v=zsGacO8u7JI&feature=youtu.be

Looks like I should avoid standing on the models flight path, the initial flight shows a stall when the model flies into turbulence generated by my body heat... Also I wonder if I should try to reduce the model decalage and also reduce downthrust, now the model seems more stable when climbing out, and makes the more severe "waterfalls" during the descent part of the flight.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 16, 2013, 08:57:54 AM
Um, forgot to add: 370mm loop of Tan II, 2000 turns wound to 40g*cm, no backoff, 880 turns left. The motor would take up to 50 g*cm if risking breakage, but 40 was a safe torque to fly multiple flights from the same motor. The residual turns are still a bit high, so maybe reducing bottom pitch and opening the spring to let model sink further before second climb would result in a longer flight. But as you see on the video, this small gym is quite turbulent and my model "waterfalls" if it hits the eddies, so tweaking out more is risky, I might easily run out of altitude after such a "waterfall".

 


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on September 16, 2013, 11:05:48 AM
I flew F1M at St. Lukes this past Saturday. I had numerous issues all day with various things breaking. One flight looked like a sure record breaker when it was at almost 14 minutes and cruising about 6' up. then it landed at 14:01 due to a loop of rubber wrapping around the prop shaft. At the end of the day I finally got the model to turn tight enough to stay in the high part of the site. It was about 30 feet up at around 11 minutes and looked like it would do 15 but then it landed at 14:09. I don't know what happened to that one.

The model I'm flying has all kinds of problems. It's mostly a bunch of old parts. The tip ribs have too much camber, the stab has been broken many times, the tail boom was adapted from my one and only F1D effort and was too weak for the F1M and the prop spars have been broken and fixed several times. Hopefully at some point this year I can get a whole new model built before I have to deal with Larry Coslick again! (Larry won F1M at USIC this year - my first loss since 2006)

I'm still using one climb. This may not be the best plan but it makes sense to me that as long as the model eventually gets to the high point of the site then it will use less energy than with two climbs. I certainly may be wrong about this.

My biggest frustration of the day was that I forgot to take my new camera that I bought especially for taking shots of flying models. Here's a camera phone shot of the F1M on its last flight. Also a short video clip near the end of the flight:

http://youtu.be/2yY_9GFoblc

Rubber data - 12.5" loop of 5/99, 1580 turns in, max torque .98 in-oz, 370 turns remaining, 86 average RPM, 14:09 flight time.


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on September 16, 2013, 12:24:16 PM
Tapio,

 Several items...

1. Very nice flying. Your prop is well-tuned.
2. The "waterfall" is a typical stall. Models in this speed range don't pitch down a lot in a stall. You need to move the CG forward and/or reduce stab incidence. You mentioned downthrust...downthrust is usually bad on these models because it requires you to use more incidence than needed on the first climb. This results in prop stall in the first descent, requiring the prop to come in sooner than necessary. The air didn't look terribly bad in that video, so I think you're just too close to the edge. It will only take a small amount of tweaking to get the model flying better in this regard, especially if you use a lower low pitch setting.
3. I'd reduce your high pitch slightly. Let it go all the way to the ceiling and bounce just a little for say 30 seconds.
4. If you are landing with 800 turns, you should be going a lot lower on low pitch. Your prop RPM at the end is much, much lower than Bill's, and I think he's using a bigger prop than you. Don't be afraid to let the model bounce around in the ceiling...Bill spends a very long time on the ceiling, more than even I am comfortable with, but he has to because of that stiff spring as he mentioned.

Do all that and you should have enough energy available to do 15 minutes or so in there.


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on September 16, 2013, 02:22:58 PM
Tapio,

1. Use thicker rubber and increase low pitch instead of lowering low pitch.  Your P/D for low pitch is already too low, in my opinion. 
1b. You may also want to use a prop with slightly smaller diameter.  Aki uses 420 mm.

2. slightly less decalage.  Got to get rid of those vertical drops.

-Kang


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 16, 2013, 03:31:00 PM
Thanks, guys, for the comments. I calculated my prop RPM, starts at 80 and tapers off to 60, then the pitch change starts and the prop accelerates to 90. I think I'll try a fatter motor first, as the bottom RPM seems quite high compared to the initial. Also the discussion of downthrust, what I intended to say that I wondered if the fact that the model only stalls during descending flight suggest that I have too much decalage and have compensated that with downthrust, and I interpret your comments that this is the way. There is no downthrust of the thrustline to the fuselage, but I'll reduce the effective downthrust by reducing the rigging angle of the wing, possibly so much to need to reduce the angle of the tailplane too. About the air in the site, it is mostly OK, but I suspect that AC in on in the dressing rooms (downstairs, but the staircase is open), as there are quite localized places where the model tends to stall. Ah well, this is a practice site anyway, too small for efficient flying. But we get to fly there every fortnight :-)

Ps. Maybe moderator could move this F1M trimming discussion to another (new or existing) thread, as this is really not related to VP's.... 


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on September 16, 2013, 04:48:55 PM
My RPM is about 89 in the video and the video was shot about a minute from landing.

I'd like to make a digital VP calibration tool but haven't figured out how to do it yet.


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on September 16, 2013, 06:03:48 PM
Here is Aki's Cat I record F1M in the last 2 minutes of flight:

http://www.youtube.com/watch?v=2BTvudH2oVI&list=PL11C0EC125B4CE40C&index=44


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 17, 2013, 12:18:05 AM
I'd like to make a digital VP calibration tool but haven't figured out how to do it yet.

Bill, what do you mean with "digital VP calibration tool"?

Aki's prop seems to be turning around 90 rpm at the end (from 86 to almost 100 when the model pitched down).





 


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on September 17, 2013, 01:50:53 AM
Several years ago I made a tool for measuring torque vs. spar rotation angle. It used most of a twisted wire type torque meter. I'd like to have something similar that uses a digital sensor like in my digital torque meters.


Title: Re: VP Hubs - for the techies among us
Post by: _shadow_ on September 17, 2013, 03:40:36 AM
This one  8)

Regards


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on September 17, 2013, 11:54:02 AM
That would be it! Pretty crude but it works (when I can find all the parts).

And for those who might not already know - you always measure the angles when you're reducing the torque. Taking measurements while increasing the torque doesn't give you much of an idea of what's happening during a flight unless you can build a frictionless VP.

I'm sure there's a way to do this with a digital torque meter but I haven't spent enough time trying to figure it out. The basic problem is that you can't twirl the digital meter with your finger like you can a spring meter.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 23, 2013, 02:52:08 AM
1. Use thicker rubber and increase low pitch instead of lowering low pitch.  Your P/D for low pitch is already too low, in my opinion. 

If I use thicker rubber, what other adjustments should I then make? For one thing, the high pitch should be increased as the max torque will increase. But then, the model would fly the first half at higher pitch, so should the spring then be also tightened, to avoid the model landing before pitch change as it will be at higher pitch in the start?

 


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on September 25, 2013, 10:15:49 AM
If I use thicker rubber, what other adjustments should I then make? For one thing, the high pitch should be increased as the max torque will increase. But then, the model would fly the first half at higher pitch, so should the spring then be also tightened, to avoid the model landing before pitch change as it will be at higher pitch in the start?

This is where it always gets interesting. Upon review, I don't think I would go to much lower of a pitch after all. I've gone as low as 20" on F1D's in low ceiling using props in the 17.5-18" range, but definitely wouldn't go any lower than that as the efficiency really starts to drop off. I would, however, try to stay with that big prop you've got, as there is much to be gained, and it doesn't look like your model is struggling with it. Your launch is definitely less shaky than Bill's, which is almost as scary as launching my F1D.

So yes, everything will change when you go to a thicker motor. I'd recommend staying at that same 550mm low pitch, maybe dropping it a little if you keep landing with unused turns, aiming to use a motor with 1600 turns or so maximum. You'll have to increase the high pitch to stay out of the ceiling, but because of the higher torque baseline, you'll probably find that you have to increase the preload. This setup is likely to force you into bumping the ceiling if you're to use up all of the turns. As mentioned before, I'd set the high pitch so that you bump the ceiling for 30 seconds or so on the first climb, then descend as far as necessary to avoid an extremely long bumping phase at the top of the second climb, setting low pitch as needed to use up as many turns as possible (meaning land with no more than 200).


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on September 25, 2013, 11:49:19 AM
The only think shaky about my F1M launches is when my hand sticks to the model. The scary part is loading a motor with over an inch-ounce of torque onto the model.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 26, 2013, 02:39:40 AM
Ok. I'll try that next Saturday (thicker motor, higher high pitch and turn in (increase) pre-tension). I have no intention to go to a smaller prop, as this one (440mm, almost 18") seems to be working good. Funny thing, the prop has the same layout as the first I built for this model, but I never got it work, as it seemed to need very thick motors and still the model could not sustain level flight after initial torque peak. I built this new prop using the same outline and pitch distribution, but with the "Kagan" method of sparless prop, and all of a sudden the model started to work much better than before. I wonder if the old one was not stiff enough torsionally; I doubt that the spar could be such efficiency killer... I recently also built another similar prop, but this has harder spring on the VP. I intend to keep this first one for Cat 1 flying as it seems to work ok for that, and try to set the new one for higher ceilings.

I did not use as high torque as Bill did, last time I would my motors to 45 g*cm max (that is about 0.63 oz*in). I guess those long motors could take up to 60g*cm (which would be almost 0.9 oz in), but I doubt they would tolerate anything more than that. Shorter motors possibly could, but then I am afraid that my practice site might get a bit tight during the initial turn...


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on September 26, 2013, 11:23:07 AM
Tapio
I just looked at the motor lengths you've posted and they look way too long for Cat 1. At my last flying session I was using 12.5" or 318mm loops. When I've tried loops about the length of yours I drop into the 12 to 13 minute range. Also according to my info Aki set his Cat 2 record of 19:39 on a 12.3" or 312mm loop.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 26, 2013, 02:20:10 PM
Ok, good. This means that (at least the bottom pitch) settings of the prop are about right.Will test shorter motors on Saturday!



Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 29, 2013, 11:39:34 AM
Not so successful session yesterday.... I tried a thicker motor, but had problems for the initial climb. With motor wound to 45 g*cm (used 40 with the thinner motors) the opening of the initial turn was more pronounced, and with the narrow flying site I tended to hit the wall. If I cheated here, picked the model from the wall it had collided and turned it by hand (practically impossible to turn the model by 90 degrees with proper steering), I still barely climbed to the ceiling. Even though I eventually set the top pitch back the where it was for the thinner motor. And then, in the descent, the model landed (even though just barely) before the VP switched. I then cheated again, increased spring pre-tension and re-launched, to make a really nice climb to the ceiling and land at 14 mins (with all the "cheat" times excluded). So the model shows good promise, if I just get the VP change earlier. I wonder if it is a deal of friction; I'll need to sand the carbon rods and add some epoxy on them, then add some graphite for lubricant...

I also tried another prop (similar layout but harder spring) on half-motors, intended for higher ceilings, but could not get that work; prop rpm to fly was way too highand the model landed at 6+ mins after exhausting all turns. Needs more work...
 


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on September 29, 2013, 12:50:16 PM
You could make a simple rig to check the VP action by using a stationary "motorstick" with a torque meter for the rear hook. Then some close up pics or videos of the hub and/or the blades while a full wind is unwinding should give you a good indication of what's happening in the air. It wouldn't be exactly the same as in flight but it should be close enough.


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on September 29, 2013, 02:35:54 PM
Hi Tapio.

I've been using silicon grease made for camera housing o-rings as a lubricant.
It doesn't seem to bind at all and works pretty well.

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on September 30, 2013, 02:33:06 AM
I took a closer look at my two new VP props. The older, with the softer spring seems to move quite freely, no binding in the hinges, so when I use the torque meter to see at what torque it meets the top stop or reduces pitch from it, there is minimal difference (indicating little hysteresis = no binding). Whereas for the newer one there is a considerable difference. I recall that I sanded the carbon pins smoother on the older one, and also recall reading the pultruded carbon tends to be quite rough on the outside, so maybe this sanding is indeed needed. Will have to sand also the newer one. And, if there is no binding problem, then I just need to wind a new, harder spring for the old prop, so that the pitch change will start a bit earlier. Looking at some torque graphs, it seems that the motor will reach 17 g*cm after exhausting some 400 to 500 turns; with rpm ~60+ this is in the ballpark of 6 to 8 mins, and this figure matches the flight pattern.

About lubrication; I hesitate a little to use any liquid lubricants, as I fear that they could pick up dust and get more sticky over time. So if I can manage without lubricant or with the graphite only I would be happier.

 


Title: Re: VP Hubs - for the techies among us
Post by: THB on September 30, 2013, 05:20:15 AM
Understand your reluctance re oil/lubes for these systems Tapio.
I imagine having to find a way to clean them periodically - and their performance becoming slower over time, between cleaning.



Title: Re: VP Hubs - for the techies among us
Post by: mkirda on October 01, 2013, 12:49:11 AM
Understand your reluctance re oil/lubes for these systems Tapio.
I imagine having to find a way to clean them periodically - and their performance becoming slower over time, between cleaning.

Far be it from me to discourage experimentation. Please try graphite and let us know how it works out for you.
The silicon grease I use is about the consistency of Vaseline. Only a touch is applied and it hasn't seemed to dry out or capture dust/dirt.
It would be pretty trivial to disassemble and clean if necessary, though I admit I wouldn't want to do that during a flying session.
My next carbon hub will be sanded smooth and I imagine I will still use the silicon grease as I have it on hand and I know it works very well.

Regards.
Mike Kirda



Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on October 01, 2013, 01:09:36 AM
I reworked my new hub last night, it seemed to bind at the high pitch so that might be the reason for ill behaviour (after initial burst the model leveled, and when the climb eventually restarted raced to the roof). I ended up sanding the carbon rods smoother, then covering with some CA (made the surface shinier). The major modification, however, was to enlarge the plastic tubes for hinges. Now the binding seems gone/less, but it will almost two weeks until I get to test that....   

Meanwhile, I think I need another spring with 1/2 turns less for my older (Cat 1) hub, to start the second climb a bit earlier.


Title: Re: VP Hubs - for the techies among us
Post by: THB on October 03, 2013, 02:43:01 AM
Hi Mike - thanks for your thoughts on this - I've never used a lubricant - or even carbon tubes - on a VP, so I'm interested that silicon works well and might give that a go. My own VPs (and props) are pretty old school and maybe time I updated a bit  :)
Following the topic with interest Tapio
cheers
Tim


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on October 12, 2013, 04:00:36 PM
I reworked my new hub last night, it seemed to bind at the high pitch so that might be the reason for ill behaviour (after initial burst the model leveled, and when the climb eventually restarted raced to the roof). I ended up sanding the carbon rods smoother, then covering with some CA (made the surface shinier). The major modification, however, was to enlarge the plastic tubes for hinges. Now the binding seems gone/less, but it will almost two weeks until I get to test that....   

Meanwhile, I think I need another spring with 1/2 turns less for my older (Cat 1) hub, to start the second climb a bit earlier.

Another Saturday night trimming session done. Indeed it was binding; with the same settings I was racing to the roof, and had to open the high pitch a little and the spring quite a lot to stop that excessive climb on a half motor (7 meter ceiling). When I eventually managed to tame the climb I was doing that "climb on burst, then some descent until the spring jumped in and the model climbed again" -stuff. SO looks like I need to wind even harder spring on this hub (too), to get onto spring sooner (at higher torque). But anyway, best flights no-touch at 7 meter hall were 7 1/2 mins on half motor, so there is potential. The next session in two weeks will not be practice but contest, in a 18meter football hall (quite a cold one), so it will be interesting to see how this prop goes on full motors!


Title: Re: VP Hubs - for the techies among us
Post by: Pit on October 15, 2013, 05:51:58 PM
How about the dry-spray Teflon (PTFE) stuff that the Heli guys are using on their mainshafts (and all other close-tolerance surfaces)?  Doesn't attract dirt so maybe it would be more suitable (but it's pricey)?

I also got my latest issue of Thermiksense, and saw that Z. Sukosd is offering VP hubs for sale.  They look quite nice (but then, I wouldn't know a good one from a shoe ::)).

Pete


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on October 15, 2013, 08:03:28 PM

SO looks like I need to wind even harder spring on this hub (too), to get onto spring sooner (at higher torque).


Tapio,

Why do you need an even harder spring instead of just adding more pre-load to this spring.  More pre-load would start the pitch change at a higher torque.

-Kang


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on October 16, 2013, 02:00:14 AM
Quote from: pit
How about the dry-spray Teflon (PTFE) stuff that the Heli guys are using on their mainshafts (and all other close-tolerance surfaces)?  Doesn't attract dirt so maybe it would be more suitable (but it's pricey)?

Might work; however seems like sanding the carbon smooth and hardening with a little CA, then making the plastic (PVC I suppose) tubing hinges large enough makes the hinges sufficiently smooth, without binding, without using any lubricant. After all, the issue is a little different from that of the heli guys: they need to reduce motion friction, we need to have the static friction (from static to moving) as low as possible to minimize binding.

Quote from: ykleetx
Why do you need an even harder spring instead of just adding more pre-load to this spring.  More pre-load would start the pitch change at a higher torque.

Even the new hinge is too soft = when movement starts, it progresses too rapidly. The symptom is that when the pitch change starts, the climbing speed increases. In order to get the climb speed (on spring) low enough, I need to reduce pre-tension until the model stops climbing or descents a bit before the change starts. If I increase pre-tension, then the movements starts earlier, and the model rushes to the roof as the pitch is reduced too early related to the motor torque -> too high rpm -> too much power -> too fast climb.

What I would need is a spring, whose torque as a function of angular movement is bigger. Thus I could add pre-tension, and have the pitch reduce at higher power, and avoid the stop/descent in the climb. But, with a harder spring, a smaller change in pitch would reduce spring force and find a new balance of torque and pitch, so that the initial movement of pitch would be less, hence rpm would not increase that much, and climb would not accelerate too much. Consequently, the range of torques (and therefore range of time) where the pitch changed would be longer, and I would not get a rollercoaster ride (climb-descent-climb-descent), but a flatter flight profile.






Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on October 16, 2013, 12:45:43 PM
Tapio,

I was under the mistaken impression that your second climb didn't go high enough, and hence you had too many turns left over, and your time wasn't as good as you wanted.  If this were the case, I would just recommend increasing the pre-load so that the second climb starts a little earlier and goes higher, allowing you to use more turns and increase flight time.

I personally would not change the spring based only on a few flights, unless the stiffness is way off, which doesn't appear to be the case.  I would first spend time fine tuning high/low pitch, pre-load, and rubber cross-section to maximize flight time.   Only after many many flights would I start thinking about changes.  Just my opinion.

In addition, it is my opinion that a softer spring is easier to trim.  When I first flew VP, I used a softer spring, and it was very easy to see visually and measure when the pitch starts to change.   I find this to be a benefit to the non-expert because from flight to flight, as VP adjustments are made, other variables aren't always constant -- namely, the rubber, which changes properties from flight to flight.  I found it beneficial that changes I made to the VP was readily observable from flight to flight.  Later, when I stiffened the spring, I found it more difficult to observe changes I made to the VP.  Again, just my opinion.

I'm a big fan of flying low-ceiling VP, and I will fly more low-ceiling next year.  Good luck with your upcoming contest.

-Kang


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on October 16, 2013, 02:50:53 PM
Quote from: ykleetx
I was under the mistaken impression that your second climb didn't go high enough, and hence you had too many turns left over, and your time wasn't as good as you wanted.  If this were the case, I would just recommend increasing the pre-load so that the second climb starts a little earlier and goes higher, allowing you to use more turns and increase flight time.

I personally would not change the spring based only on a few flights, unless the stiffness is way off, which doesn't appear to be the case.  I would first spend time fine tuning high/low pitch, pre-load, and rubber cross-section to maximize flight time.   Only after many many flights would I start thinking about changes.  Just my opinion.

Just in case I did not make myself clear enough: I have 2 of these new props now. The first showed such promise for low ceiling, that I decided to put it aside for such work and built another one. For the second I made a little harder spring, but not hard enough it seems. The latest session was trimming the second prop on half motors. Again in the 7 meter (22 foot) ceiling, so the aim was to trim model for a 15+ meter hall. With this prop I had problems of the second climb going too hot, until opening the pretension to a point where the model came down a bit before starting the second climb. Too soft.


Quote from: ykleetx
In addition, it is my opinion that a softer spring is easier to trim.  When I first flew VP, I used a softer spring, and it was very easy to see visually and measure when the pitch starts to change.   I find this to be a benefit to the non-expert because from flight to flight, as VP adjustments are made, other variables aren't always constant -- namely, the rubber, which changes properties from flight to flight.  I found it beneficial that changes I made to the VP was readily observable from flight to flight.  Later, when I stiffened the spring, I found it more difficult to observe changes I made to the VP.  Again, just my opinion.

I agree that soft springs are easier to get to decent performance. And then, you should get more time by not wasting energy for the climb (on higher rpm) but keeping constant height. So looking for to bend a new spring....

Quote from: ykleetx
I'm a big fan of flying low-ceiling VP, and I will fly more low-ceiling next year.  Good luck with your upcoming contest.

Thanks. Too bad there will not be the IIFI contest, that would have been nice. The site for the next contest is a bit challenge; tends to turn cold in winter and heating is via air conditioning, so the air indoors may not be that good all day. Hopefully for some periods though.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on January 08, 2014, 07:18:38 AM
Following up the F1M hub in message #51 (http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=2318.msg118091#msg118091) I used the same construction for F1D. Here the cross bar is 0.5mm dia carbon rod, and the hinges are short lengths of teflon tubing (from cyano bottle add-on). I still cannot understand how Kang builts his hubs (http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=13948.0) to 70mg, this one is almost double: currently 125mg. Ok, I should shorten the rubber loop on the shaft, and for final versions discard the paper tubes and glue to hinges directly on prop spars. That should save some 10 to 15mg.

I do have more carbon on this, for a reason: I want to have the prop attachment more rigid, have the hinge points further apart. This should reduce the play on the blades and also reduce catching of the hinges, as torsional loads on the bearings would be smaller.

Had to do some thinking with the adjustment screws. 00-90 sized nylon, the heads are terribly heavy. So I cut them off, and tried to cut a slot for screwdriver in the end. No luck, the resulting slot is too weak and fails quite quickly. So after a little thinking I recalled the way to make the line release on silicon damper viscous timer: a cross har out of carbon rod. Tried the same on the setscrew, and voila! it works. Just had to make and adjustment tool from a piece of aluminum tubing, which I cut square and dremeled a slot to the end.

Did some test hops today, and the hub withstood maximum rubber torque. There is one modification I need to make: now the adjustment screw holder is attached to the 0.5mm carbon rod only, and this is a bit flimsy to torsion. So I need to lengthen the 0.5/1.0mm tubing in the center slightly, and attach the adjustment fork directly to that piece    


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on January 08, 2014, 08:17:49 AM
I think nylon will melt safely. You should be able to use some metal tubing that will slip over the 00-90 screws. Squeeze that about 2-3 mm from the end all the way flat. Then heat the end and push a 00-90 screw into it. The nylon should deform to the inside shape of this tool. Remove and cool. The end should be shaped kind of flat and the tool can be used to turn it.

I haven't tried the above, but it should work.

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on January 08, 2014, 08:58:01 AM
Ahh, neat idea. Did not come to think of that, even though I have melted nylon before. Anyway, added a third picture above to show the screws with crossbar. these are work nice with the tool made of tubing.



Title: Re: VP Hubs - for the techies among us
Post by: leop on January 08, 2014, 10:10:12 AM
Hi,

I use flattened screw ends on all nylon adjustment screws on my vp hubs since I started building vp hubs two years ago.  I do not heat the ends but rather just flatten the ends with needle nose pliers.  As one can see in the picture, I mark the end of the flat (using a marking pen such as a Sharpie) so I can see the screw alignment both to fit the "socket" tool for adjustment and to record the adjustment.  The adjustment "socket" tool is just a 3/32" brass tube flattened at the end (again with pliers).  For those of you who are not impaired with non-metric dimensions, a 2.5mm tube works.

One good result of using this screw method is that one can get three adjustment screws out of one pan head nylon (#00-90 by 1/2" for us non-metric folks).  Being able to get three adjustment screws as well as ease of adjustment was why I originally thought up using a flattened end.  As I said above, I have been doing this for two years now with no problems.  I did add some white heat shrink tubing to the "socket" tool so that I have a better grip and also so that I can see and distinguish the tool from plain brass tubing.

LeoP


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on April 28, 2014, 03:40:29 AM
Referring to my message #91 (and a couple of others preceding it); seems like my voes about too soft springs actually are a symptom of the hub still binding. I'm preparing for a competition in a Cat 1 site in a few weeks, looking to try to make a new record there, so last Saturday I was full-motor testing my F1M in the 7 meter (21ft) site I use for practice. One flight climbed a bit too much, and kept colliding with the ceiling from 2 to 7 minutes, then lost a little height and climbed the the ceiling again at 8 to 9 mins. Most collisions were gentle, so I managed to keep the plane centered in the narrow hall with lots of steering. Landed at 13 mins sharp. Then I tried another one, opened high pitch by a quarter turn and also opened the spring a little. This time I only climbed to 6 meters and landed at 5:40 still at high pitch. I picked the model and relaunched next to the floor, and the model climbed away to reach 6 meters again, and landed at 12:35. So it seems to me that the hinges are binding and they need an external "tap" (from landing or hitting the ceiling) to switch to a smaller pitch angle. I suppose it is not time to add some graphite first, then silicone later if graphite does not work, to see how to make the hinges better....   


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 04, 2014, 01:41:09 AM
Another Saturday, another test session. Yearlier this week I had taken the hub apart. Sanded the carbon rods that are one part of the hinges, they came out so dull that I decided to put some CA on them for a smoother surface. When assembling, the hinge tubes on the prop spars were really tight and stiff. Hmm, maybe the hinges were binding? After some thinking decided to drill the tubes out with 1.2 mm tip (the carbon rods were 1.0mm). After assembly, the prop felt to work more smoothly, I thought I could better feel the varying spring force when twisting the hub.

So onto testing. Air was not as good this time, had some problems with model stalling, which of course is a bad thing when you try to adjust the model for a 2-climb pattern. After some tweaking ended up with almost the same settings that I started with. Final flight climbed to 6 meters, then came down to 3 before climbing again and hitting the ceiling for half a dozen times. Landed at 12'39". 1800 turns in motor, 40 backoff (44 to 35 g*cm torque). Landed with 700 turns, average RPM a little under 90. I still would have room to climb a bit more (less backoff), but then I would also need to open up the spring a bit. Also it seems that my spring is still a bit too soft (to get consistent level flight). But most of all, the major issue indeed seemed to be the hinges binding, and looser tubes for hinges helped here!

 


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on May 04, 2014, 09:17:35 AM
Hi Tapio.

If you have any idea of the torque range desired, I could probably help with a spring.

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 05, 2014, 01:13:02 AM
Thanks!

I think that the next thing I should do would be to wait for the contest (in two weeks time) and then a) take videoclips of the flights to count prop RPM and estimate altitude at various phases of the flight (easier to do for F1M from viddy, as the typical RPM is around 90), and b) record the unwinding torques of the motor I used. Thus I could try to construct the pattern of pitch change, motor turns and vertical speed of the flight, and maybe try to estimate, what kind of pattern of torque vs. angular deflection I would need for the spring.



Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 18, 2014, 02:02:45 PM
We had the contest today. I did manage to improve the record, from 11:19 to 12:09, but compared to the test flights, that was not a especially good result. Moreover, I always landed with lots of turns remaining (wound the motor to 1900 and landed with 900). Some time ago Kang commented that I should use thicker motors, and indeed I agree. The thing is that this means setting the high pitch and spring setting completely different. So I feel I should start with those, and then think about the spring dimensions once  got the high pitch into the ballpark...

The thing that worries me is at even currently the model seems to fly quite flat at high pitch and torque, so it may be that I need some aerodynamic changes to the model (shorter motor tube, CG forward) to be able to fly the model with fatter motors....

   


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 19, 2014, 12:36:18 AM
The thing that worries me is at even currently the model seems to fly quite flat at high pitch and torque, so it may be that I need some aerodynamic changes to the model (shorter motor tube, CG forward) to be able to fly the model with fatter motors....

I should have added, that I have tried to add and tighten the rigging for the model, so I doubt that this is a issue of the motor tube bending; or if it is it is also a matter of the model being extremely sensitive to very slight tube bending.

Also my model is highly sensitive in pitch, and occasionally when hitting some turbulence, both wing and tail stall, and the model loses considerably altitude coming down flat, before regaining horizontal flight speed. Thus moving the CG a bit forward might help. Currently my CG is at 120%.


Title: Re: VP Hubs - for the techies among us
Post by: abdee1983 on July 04, 2014, 04:44:29 AM
oh..very good planes


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on July 30, 2014, 09:03:52 PM
I've started on a new F1M and tackled the VP first. This one took a day to design and 2 days to build. If I were doing 3 or 4 more I think I could get it down to 3 or 4 hours. Weight is about 235mg - partly because I repaired a couple of breaks instead of replacing the part. 200mg might be possible by making everything a little smaller.


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on July 30, 2014, 09:12:35 PM
I've started on a new F1M and tackled the VP first. This one took a day to design and 2 days to build. If I were doing 3 or 4 more I think I could get it down to 3 or 4 hours. Weight is about 235mg - partly because I repaired a couple of breaks instead of replacing the part. 200mg might be possible by making everything a little smaller.

Nice!

What are you using as a spring, Bill?

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on July 30, 2014, 09:40:10 PM
Wire!

Oh - 5 turns of .013".


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on July 31, 2014, 07:30:17 AM
Looks great, Bill. Much better job on the spring than I could do. I would recommend checking alignment, though. Everything's surely functional, but the forward shaft segment is not parallel to the rear. If you look really closely, you'll see that it points off to the left. I only notice this because it's a problem that plagues me. There's nothing worse than a snagged blade because your hub isn't straight!


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on July 31, 2014, 10:48:28 AM
Everything was trued up after the blades were installed. Unless you're a much better builder than I am the final alignment is pretty difficult to predict ahead of time. Now Nick Ray could probably mass produce hubs and blades and have them all interchangeable!

BTW - This is the first hub I've built since about 2005. My F1M's have all used the same hub since then.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on August 08, 2014, 12:48:16 AM
Perfect springs are super easy to make if you use the technique described by Steve Brown in his VP article from about 20 years ago.  The springs in the background are 9 turns of .009", and they only take a minute to form using the mandrel and hypodermic tube with a tooth on it that you can see in the foreground.  For an F1M spring I would use a larger mandrel and bigger hypodermic tubing to form it, but the process would be the same.


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on August 08, 2014, 11:07:02 AM
I use the K. Fags spring tool. The only problem with that is that you have to manually straighten out one of the ends after bending the spring. I'll try Steve's method if I do another one.


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on August 22, 2014, 09:53:43 AM
I had a problem with my last VP being too flexible at the junction of the driver arm and the prop shaft. This caused the driver arm to slip off of the high pitch screw a couple of times. I spent (wasted) a day trying some different ways to fix the problem and finally came up with this design. The basic idea was to make a solid "T" member with the driver arm and the middle carbon tube. The joint where rotation occurs is under the top tube of the hub. A short piece of hypo tubing acts as a bearing for the top bar. There is very little movement possible between the two parallel members, but I also thickened the driver arm where it hits the screws to make sure in doesn't slip off in high torque launches.

As usual the drawing looks a lot better than the finished hub!


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on November 24, 2014, 08:21:52 AM
Referring to my messages #102 and #105 above, it seems that I have found a solution to the hinging problem. Before a contest yesterday, I took the hub apart, sanded the carbon rods extra smooth where the hinge-tubes come (there were some traces of CA clumps there), then added some graphite with a pencil. Yesterday the hub worked smoothly, no signs of binding but the climb leveled at altitude for a while, then model started climbing again without coming down before the second climb started. Also the second climb started on several flights at practically the same time, which indicates that the hinges are not jamming. Also I had moved the rubber back hook 10cm (4") forward, so my hook to hook distance is now about 30cm (12"), and with this move the model is now positively climbing even at higher torque. Not going flat any more as it used to be. Best flight 14 minutes in 11m hall, but still room to improve, as the second climb was too high, and had plenty of turns left when landing. I suppose I should go to still fatter motor and use higher pitch initially.




Title: Re: VP Hubs - for the techies among us
Post by: Olbill on November 24, 2014, 10:39:46 AM
I think moving the hook was a good idea and shorter motors would probably help. Here are the motor lengths for my record flights:

Cat 1 - 11"
Cat 2 - 11.13"
Cat 3 - 12.5"
Cat 4 - 12.75"

I guess it should be noted that average RPM's with my latest prop were in the 70's for all of those flights.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on November 25, 2014, 09:02:04 AM
Ok, useful data, thanks.

My motor for the 14' flight was 340mm (13.6") long, I wound it to 1500 turns and had about 500 left when landing. So I still should go to somewhat fatter motor. My calculated average rpm for that flight was 76 rpm.



Title: Re: VP Hubs - for the techies among us
Post by: Maxout on November 25, 2014, 09:38:46 AM
Tapio, that sounds mighty fine. 14 minutes is an excellent time. Before you increase the high pitch too much, consider backing off on preload a touch. Half motor testing is really useful for judging what the climb profile will actually be.

One of these days I'll actually fly my F1M. It has come to I don't know how many contests and has yet to come out of the box.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on November 25, 2014, 10:53:46 AM
With the current motor, yes, I should open the spring pretension a bit. The flight profile was a slow climb to about 7 meters, flattening out there and then starting to climb again at 3'45". This second climb ended all the way to the ceiling and scratched there for quite a while. So less pre-tension would have delayed the start of that climb.

Yet, I used to fly my F1M on 380mm motors (they were good for my then smaller diameter prop, so I started with those) that took about 200 turns and then I landed with 1000 turns left. Now I have tweaked my prop to handle the 340mm motors, which take 1500 to 1600 turns and land with 500 to 600 turns left. So it seems that 14 minutes takes 1000 turns. I guess I should aim for 1200 turns used for the flight (in Cat 1 to Cat 2), and still shorten the motor a bit for this aim. But then a fatter motor would mean higher torque throughout the flight, so I suppose it would mean some more tweaking of the prop.... both high pitch and pretension.


  


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on November 25, 2014, 03:03:52 PM
Here is the data for Aki's F1M flights:

Cat, wind - unwind, remaining
Cat1, 1640-21, 147, 17:39 (83.4 RPM)
Cat2, 1760-21, 150, 19:39 (80.9 RPM)
Cat3, 1770-20, 24, 21:01 (82.2 RPM)
Cat4, 2020-10, 265

We can roughly deduce the motor lengths.  He doesn't go below 1600 turns, even in Cat I.  In Cat I and II, his flights finish with ~9% of turns.  This data give another set of references.


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on November 25, 2014, 04:28:28 PM
With the current motor, yes, I should open the spring pretension a bit. The flight profile was a slow climb to about 7 meters, flattening out there and then starting to climb again at 3'45". This second climb ended all the way to the ceiling and scratched there for quite a while. So less pre-tension would have delayed the start of that climb.

Yet, I used to fly my F1M on 380mm motors (they were good for my then smaller diameter prop, so I started with those) that took about 200 turns and then I landed with 1000 turns left. Now I have tweaked my prop to handle the 340mm motors, which take 1500 to 1600 turns and land with 500 to 600 turns left. So it seems that 14 minutes takes 1000 turns. I guess I should aim for 1200 turns used for the flight (in Cat 1 to Cat 2), and still shorten the motor a bit for this aim. But then a fatter motor would mean higher torque throughout the flight, so I suppose it would mean some more tweaking of the prop.... both high pitch and pretension.


Unless you're against the high pitch stop it seems like a much easier route to just add high pitch until the climb matches the space. I don't worry about pretension unless I can't get what I want with the high pitch screw.

My 11" Cat 1 had 1400 turns, launched at 1.06 in-oz with an average RPM of 74. The pitch settings were 65/26.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 06, 2015, 02:37:43 PM
Another trim session, preparing for a Cat II competition in a few weeks. I have been adjusting my VP2 prop, and based on previous sessions, cut new, fatter motors, 160mm long loops for a half motor (so 320mm, 13in for full motor). Wound the motor to 60 g*cm (0.85 oz-in?), the half motor took 800 turns. Flights around 8'45 secs and landing with 50 turns means average 79 RPM. The prop adjustment is good for initial climb (to about 6 meters, the hall where I fly is 7m) and slight descent after that. The second climb, however, was too much, as the model climbed to the roof and collided there a few times. I tried to increase the bottom pitch to reduce RPM, but it did not help. So I guess the better adjustment is to open the spring and delay the second climb.

I shot a video of the flight. Once I get the time I'll count the RPM's to find out exactly when the VP changes. But meanwhile, here it is: https://www.youtube.com/watch?v=vuQDe_z_HZY
 


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on May 06, 2015, 03:58:20 PM
Tapio, first of, let me congratulate you on an impressive flight time that if extrapolated to a full motor, could win for you at most contests.

Now, you're not descending back down enough on high pitch, and you're climbing much too fast at the beginning (my F1M doesn't climb more than 3-4 feet on high pitch, but I have a stiff spring on it). I'd increase your high pitch 1/2 turn. Then unscrew the preload until the model descends at least halfway to the floor before climbing again. At the actual contest, continue decreasing the preload until the model either descends to the safe limit (head height in most cases--where the air becomes turbulent) or the model only taps the ceiling for 60-90 seconds. I've found that to be the most efficient flight profile. Any more than 90 seconds of ceiling bumping is wasted power. Any less and you can't consistently reach the ceiling.

Never increase low pitch to limit your climb. Low pitch is set to achieve climb at the lowest possible torque. The only time that can hurt you is if you're landing with too few turns. Otherwise, you vary high pitch and preload, and even the spring if necessary (I think your spring is pretty close in this case). You should be able to get up to 9:20-9:30 by tweaking the high pitch and preload.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 07, 2015, 04:45:44 AM
Thanks!

A few comments: I landed with 50 turns remaining and the model seemed to start sinking quite rapidly, so I think it is about the end of the available turns/torque. With 79 average rpm, 50 turns would be good for 30+ seconds, but to be able to drain them I would have needed much more altitude. Actually that was the reason I tried to increase the bottom pitch, to lower the RPM and make the turns last longer. But alas it did not seem to have much effect on the flight.

I might try adjusting the high pitch, but on the other hand, the adjustment seems very sensitive. I think I increased it a little (half turn or quarter) to stop serious ceiling scraping into this 6m climb, so I fear that if I open it up much, I will stop all the climb. Even now the flight pattern is such that the model climbs to 5 meters in 30 seconds, and the levels off, gaining very little extra altitude after that initial burst, so I need to be careful with that adjustment, to get enough altitude but not too much.

Indeed I should open the spring to let the model sink to lower altitudes before the prop reduces pitch and model climbs again. Remains to be seen if that gains much more duration, while of course it would reduce the risks when avoiding ceiling contact.

This was actually the first motors I cut from a batch of 99/7, and the rubber seems to be quite good. I feel that I got a bit more torque than from 99/5 of similar loop length, and yet the number of turns was comparable. I had used 160mm half motors of the later before, they took about the same turns, but landed with more turns on. I might even be able to squeeze in a bit more torque, as I have would two half-motors to that 60g*cm torque a couple of times now, and no breakage so far. On the other hand, that seems to be at about the upper limit of torque that the model is able to handle, as letting the prop turn just a few turns before launch makes the launch pattern much nicer compered to launching right away, which makes the model bank to the left and make a wide open initial turn (bad thing in such a small gym as I fly in!) before the initial torque burns off and model resumes more normal flying attitude. The launch on the video is with the higher torque, and it barely avoids colliding the basketball hoop on the left wall... :-)


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on May 07, 2015, 07:29:18 AM
A few comments: I landed with 50 turns remaining and the model seemed to start sinking quite rapidly, so I think it is about the end of the available turns/torque. With 79 average rpm, 50 turns would be good for 30+ seconds, but to be able to drain them I would have needed much more altitude.

For cat II, 50 turns is an admirable amount to land with. I wouldn't try to use up that last bit. Save it for a warm day (the hotter it is, the more of those turns you'll use up).

Actually that was the reason I tried to increase the bottom pitch, to lower the RPM and make the turns last longer. But alas it did not seem to have much effect on the flight.

Yeah, unless you go below the optimum low pitch, you don't gain anything from increasing the pitch in hopes of slowing down the prop (actually you usually lose performance).

I might try adjusting the high pitch, but on the other hand, the adjustment seems very sensitive. I think I increased it a little (half turn or quarter) to stop serious ceiling scraping into this 6m climb, so I fear that if I open it up much, I will stop all the climb.

Try another half turn. As fast as it's climbing, you're still not terribly close to stalling the prop. If it does start showing signs of stalling (the prop, not the wing), reduce your bracing tension ever so slightly to get the nose to stay lower on launch (and only a tiny bit lower). Like I said, my own F1M only climbs a few feet at full torque, then just hangs out there at the same altitude for several minutes before starting a slight descent and then climbing back away. You're ahead of me on performance, but my prop is old and pitiful. ;) I do typically find that peak performance occurs when you climb to roughly 2/3 of target height on high pitch, then descend back and climb all the way up with a couple light bumps on low pitch. The stiffer your spring, the lower the optimum becomes for your first climb because you need to start "climbing on the spring".

Indeed I should open the spring to let the model sink to lower altitudes before the prop reduces pitch and model climbs again. Remains to be seen if that gains much more duration, while of course it would reduce the risks when avoiding ceiling contact.

It always gains you time to descend more if you're bumping the ceiling. Anytime the model is bumping the ceiling, the prop is spinning faster than it needs to. The amount of bumping that you were doing indicates that the model is losing several minutes of flight potential (in full motor terms--you're losing about 1 minute on your half motors).

On the other hand, that seems to be at about the upper limit of torque that the model is able to handle, as letting the prop turn just a few turns before launch makes the launch pattern much nicer compered to launching right away, which makes the model bank to the left and make a wide open initial turn (bad thing in such a small gym as I fly in!) before the initial torque burns off and model resumes more normal flying attitude. The launch on the video is with the higher torque, and it barely avoids colliding the basketball hoop on the left wall... :-)

Here's the solution: wind your motor and let it sit for a moment while you carry your steering pole out to your launch site. Remove a small segment of the pole so it will be manageable (like to top two sections if it's a put-over). Now go back and load up the plane. As soon as the model leaves your hand, reach down and grab the short pole segment and follow the model, steering by the tailboom as required. Usually after the first circle or two the model will stabilize, but you need the rest of the pole present to quickly extend those top segments as the model climbs.

Any power you leave off because the model won't turn at that power, that's wasted energy and lost seconds (or even minutes) on the clock.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 07, 2015, 08:11:44 AM

Um, that was 50 turns on the half motor, so it is 100 for the full motor, and that would be a minute... My mistake. Anyway, thanks for the comments, I'll try to open up the top stop and also slightly the spring. Next session will actually be the contest day, 2 weeks and 3 days from today! :-)

 


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 08, 2015, 07:40:32 AM
It always gains you time to descend more if you're bumping the ceiling. Anytime the model is bumping the ceiling, the prop is spinning faster than it needs to. The amount of bumping that you were doing indicates that the model is losing several minutes of flight potential (in full motor terms--you're losing about 1 minute on your half motors).

I have been thinking about merits of two climbs vs. changing the prop pitch continuously to sustain altitude, and came to think that actually when a model is climbing it is converting rubber energy into potential energy (altitude), which it can then later exchange to duration, when (in descending flight) less energy is required for the flight. From this perspective it is obvious why ceiling bumping is bad - the model is burning the energy, but as the ceiling limits the ascend, the excess energy is wasted.

Still I could not figure out whether it would be better to make two climbs or not. I guess it eventually boils down the to the variation of prop efficiency at different pitch; it would be most efficient to fly as long as possible with the best efficiency.


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on May 08, 2015, 08:42:19 AM
Still I could not figure out whether it would be better to make two climbs or not. I guess it eventually boils down the to the variation of prop efficiency at different pitch; it would be most efficient to fly as long as possible with the best efficiency.

Bear in mind this is theoretical and based largely on empirical data from F1D flying, but I'm going to throw it out as a possibility.

My experience is that all of my attempts at flying a single climb in low ceiling result in extremely high (90-100") high pitch settings, which for most blade designs stalls out the blade roots (this typically increases rather than decreasing launch RPM, so it's blowing power out the window for no return). Also, the spring required has to be fairly stiff to bring the prop pitch down early on, and since it's a linear curve, but the rubber torque is nonlinear, it's almost impossible to get the prop onto the low pitch stop prior to reaching minimum-torque-to-climb without excessive ceiling bumping. More to the point, it's proven completely impossible for me. Folks like Kornichuk have solved that by going to two springs, but I'm resisting as long as possible. The single climb, for F1D at least, starts to become a possibility in high Cat II ceilings on up, which interestingly is where Brett Sanborn has dominated. It's interesting to note that in conversations with him, Brett has described Cat I as a total mystery to him.

So at the end of the day, it would appear that the dominant efficiency factor is to just stay off the ceiling while still beingat the ceiling when the model reaches minimum-torque-to-climb. If that requires the model to climb all the way up, descend within 6" of the floor, and then climb all the way back up, so be it.

I will say that the pitch settings for high pitch cruise and low pitch climb/descent are drastically different. If I could have a VIT on my model to add 1.5 degrees incidence just as the pitch starts dropping, I could add 2 minutes or more to my flight times. I found that I could get a model to stay at the ceiling on high pitch for more than 10 minutes when running 1 degree incidence, but that was too little incidence for it to climb at all on low pitch. I even tried grabbing the model out of the air and adding in another degree of incidence after the pitch change started, and the model climbed all the way back up to the ceiling when it normally would not have been able to climb halfway back up.

Perhaps it's time for me to cook up a gadget...great...like I need another gizmo with a torque adjuster screw!


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on May 08, 2015, 08:57:31 AM
I thought that was one of the functions of having slack in the bracing wire.


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on May 08, 2015, 11:24:32 AM
I thought that was one of the functions of having slack in the bracing wire.

I tried that. The stick bends back too quickly. Causes the model to go flat at full torque, then the prop stalls 90 seconds into the flight, the model falls back to the floor, and oh, if you have the preload high enough, it climbs happily away just before it hits the floor. And you end up 3 minutes behind everybody else. ;)


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 08, 2015, 01:25:00 PM
Interesting discussion.

Now, first of all, I assume that above when Joshua says "pitch" referring to the different settings needed for high pitch cruise and low pitch climb, he means decalage? Or is that also called pitch.

Anyway  find it curious that different decalage would be needed. I would assume, that the optimal decalage for given trim speed (i.e. prop thrust) would be constant. I cannot see why prop settings would affect the trim settings. Except maybe one feature might affect: if the motor stick twists, it adds angle inboard and reduces it outboard. And as (if) the wing has offset, then these two wing halves are different. So adding wing twist will also increase the angle. Maybe this is the reason the model becomes under-elevated at low pitch setting (it is actually low torque condition)?

Short of that, I find the CG location and decalage the most important feature impacting the model trims at different phases of flight. I used to have long (400mm, 16in) peg distance on my F1M's. They are ok for low ceilings, but tend to go flat on high torque launches. No problem if the ceiling is low, but bad if you aim for a high ceiling. It was not a matter of bracing, as much I tightened it or added new thread, the model still went flat. Moving the back hook forward (hook distance is now 300mm, 12in) changed the model behaviour completely. Positive climb at high torque, no problem of tucking in. I conclude that CG more forward and more decalage was the cure. Then for F1D the CG is still further forward, and the problem (as in Slanic salt mine) is the opposite, the model tends to pitch up too much on launch. In 2014 I tried to loosen the rigging, but had the same experience as Josh mentioned, it helps for the initial launch, but in 20 to 30 seconds the model pitches up and stalls. I assumed that this is because the motor looses the torque peak, and the motor tube straightens. Too early for a safe steep take-off.


Title: Re: VP Hubs - for the techies among us
Post by: Maxout on May 08, 2015, 02:44:20 PM
Now, first of all, I assume that above when Joshua says "pitch" referring to the different settings needed for high pitch cruise and low pitch climb, he means decalage? Or is that also called pitch.

Notice I've been talking in terms of pitch and incidence. Pitch means prop pitch. High prop pitch for first climb, low prop pitch for second climb. Ok, we're past that bit...

You need the model to fly faster than normal with the prop at high pitch. There's an optimum forward speed at which the model can climb at a higher prop pitch, and hence lower rpm, than the speed needed to achieve a climb at the minimum-torque-to-climb. If you can hit both of these, you can achieve a major improvement in flight times. Now, there are some tricks to this. Big, low camber stabs are particularly useful in low ceiling flying and produce a model whose pitch trim (pitch attitude trim, not prop pitch), and hence equilibrium airspeed, changes according prop pitch setting. My models fly at greatly elevated speed at high torque, and they slow down as the torque backs off and the prop pitch starts changing over. Unfortunately, some of that change is torque dependent, so the model starts pitching its nose up as the torque backs off. When this happens (around 5 degrees nose up), the root of the descending blade starts to stall. So the blades end up stalled during an ever increasing portion of their rotation. This causes the characteristic shuddering or "nose wag" of the model as the prop rotates from horizontal to vertical. As soon as this blade stall and nose wag start to become significant, the model starts descending, often at a torque setting high enough that it's still capable of a climb were the stab incidence lower. Problem of course, is that this lower stab incidence corresponds to a setting at which the most simply will not climb at low pitch. And thus this unending cycle continues...

None of this is a major factor in high ceiling flying. You can just add downthrust to prevent the stalling that tends to occur 2-3 minutes into the flight, and the cruise doesn't suffer that much. Still further, you can set the stab to zero incidence and put all the incidence in the wing, and off you go. Cailliau and Kang Lee both use this trim setup with results that speak for themselves.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on May 08, 2015, 03:08:41 PM
When you move the incidence to the wing you are actually increasing prop downthrust relative to the model flying attitude.... Which would increase the pitch down moment of the motor thrust at high torque.


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on May 09, 2015, 11:51:04 AM
Tapio,

Adding wing incidence isn't the same thing as adding down thrust.  When you actually add downthrust at the bearing, for example, the thrust line changes relative to the center of gravity and center of drag.  Adding wing incidence does not change the thrust line relative to the center of gravity.

I think it's better to think of downthrust as decreasing the amount of up moment.  Too much up moment is the common problem we face in a high-ceiling launch.

-Kang


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on May 09, 2015, 01:49:23 PM
And of course adding down thrust to the bearing pinches the prop shaft causing an unbearable* increase in friction losses as does adding side thrust at the bearing.

*(to me any increase in friction loss is unbearable)


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on May 09, 2015, 03:59:43 PM
Having incidence in the wing (instead of only in the stab) changes the thrust line relative to the direction of flight.  That is, you can fly less "nose up" trim, or you can have "nose level" or "nose down".   I'm not sure how exactly this helps with high-torque launches, but it does.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on March 01, 2016, 08:23:20 AM
As this thread is now more about adjusting the VP prop than constructing it, I'll carry on. WIthin a year I have had a few good sessions at my local 7 meter (sub Cat I) gym and full motor with a prop dedicated for Cat I, so I called for an option to try a Finnish record. My test flights had shown that I should aim for a 310mm motor. On the first outing I broke my only ones at that size, so had to try a 285mm (11.4") motor. Only succeeded 13 1/2 minutes. The interesting observation was that with a shorter motor, the model descended a longer time after the first climb. I had noticed this before - use thinner motor than the prop is trimmed for, and the second climb starts earlier & higher! With the short motor I was struggling to get the second climb to start before the model landed at high pitch.

So for the second session two weeks later I cut some new 310mm (12.4") motors. With the first motor had some trim problems, and second try on the same motor did not climb, so I took another one. Tan II 99/7 (seems like as good rubber as 99/5) took 1360 turns to max torque of 49g*cm (0.7 oz in - pathetically low!). No backoff. The model climbed too hot to hit the ceiling in less than two minutes. Almost hung up and tail slided to half the hall height. After that it came down a bit and started another climb at 7 minutes. The second climb was a metre or two short of the ceiling, so without the tailslide the flight would have been longer (as second climb would have gone all the way to the ceiling). While descending it also hit a basketball ring and lost another meter of height. Also the flight needed a lot of steering, probably due to heating the air in the gym was drifting a lot. Despite all problems I got 14'14", a new Finnish record. I think there would be potential to make 15 minutes even in that hall. I shot a video of the flight (to be able to count the prop turns and thus analyze the VP functions later): https://www.youtube.com/watch?v=whrPWIzs98U

Landed with 280 turns, average RPM 72, so there would have been room for a slightly longer flight, if there were not the collisions with the ceiling and the basket ball ring. Also worth noting the the altitude loss and climb after the tailslide was less than half the site height, so with this 310mm motor the flight was level for a good part of it. As said, with 285mm motor (taking 1200 turns) the 7 meter height is barely sufficient for the descent after touching the ceiling!



Title: Re: VP Hubs - for the techies among us
Post by: Maxout on March 01, 2016, 10:46:00 AM
Wow. Tough conditions. If you could get smoother air it would add a lot of time. The amount of energy being wasted on just maintaining altitude in that turbulence is significant. I do think you can do over 15 if you can just get smoother air.


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on March 01, 2016, 02:14:11 PM
That would be in May. While the heating is on, there will be turbulence in such a small hall. On the other hand, I'm looking forward to IIFI as I suppose that would be an excellent Cat I site...


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on April 30, 2016, 12:13:18 PM
From Russian, with Love.


Title: Re: VP Hubs - for the techies among us
Post by: ykleetx on April 30, 2016, 04:56:21 PM
My mistake. Properly sourced, the tagline should say

"From Serbia, with Love."

(VP by Slobodan Midic)


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on June 29, 2016, 12:40:14 PM
I thought I would add a couple pictures of my new VP hub.  I used this hub for the first time at Kibbie, and my best time was 26:18.  I'm planning to build a couple more with minor refinements as I prepare for the team finals next year.


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on June 29, 2016, 08:18:34 PM
Very nice!


Title: Re: VP Hubs - for the techies among us
Post by: spr on June 30, 2016, 05:43:40 AM
Interesting design, Jake! 

What are the dimensions of carbon tubing in centerpiece and spars? Weight? Apparently there was no frictional sticking issues as I look at you great times in Kibbie.

Simo


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on June 30, 2016, 11:57:52 AM
The center spar is off the shelf 1mm OD carbon pultrusion with a .013" ID hypodermic tube for the shaft pivot.  The prop spars are 1mm ID pultrusion sanded down to 1.2mm OD.  The finished hub minus spars only weighs about 90mg, but the finished prop is heavy due to the carbon spars and prop blades.  This particular prop is 343mg, but it shouldn't be difficult for me to shave 15-20mg off of future props and bring the total weight down to 320-325mg.  In the end I still needed 100mg worth of spacers and 15mg of ballast to bring the model up to 1.4g, so weight wasn't a big issue

I spent some time working Teflon dust into each hinge to reduce friction.  Although I do believe they may have been sticking a little, the prop shifted consistently and my half motors lined up well with my full motors.  It also didn't shift after steers which would indicate it wasn't sticking too much.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on December 20, 2016, 05:52:42 PM
The center spar is off the shelf 1mm OD carbon pultrusion with a .013" ID hypodermic tube for the shaft pivot.  The prop spars are 1mm ID pultrusion sanded down to 1.2mm OD.  The finished hub minus spars only weighs about 90mg, but the finished prop is heavy due to the carbon spars and prop blades.  This particular prop is 343mg, but it shouldn't be difficult for me to shave 15-20mg off of future props and bring the total weight down to 320-325mg.  In the end I still needed 100mg worth of spacers and 15mg of ballast to bring the model up to 1.4g, so weight wasn't a big issue

I spent some time working Teflon dust into each hinge to reduce friction.  Although I do believe they may have been sticking a little, the prop shifted consistently and my half motors lined up well with my full motors.  It also didn't shift after steers which would indicate it wasn't sticking too much.

I just got a 0.7mm carbon fibre tube and a 0.28mm carbon fibre rod in. I'd really love to have a go at a vp myself. I've got several Tregers and they are very nice indeed if at times a bit delicate. I'd like to try to make a vp with a very supple hinge and perhaps a bit stiffer and lighter than music wire, which is why I'm thinking of carbon inside a carbon tube. I also like the idea of carbon drive pins. I just find that when you load the motor all kinds of things can go wrong with driving pins popping out etc. As Jake says a drill press is handy and anything Dremel seems dubious I've been looking at buying a Proxxon, but I can see that drilling a hole through a tiny carbon tube is going to take not just a drill press but quite a precise small vice.
Hans


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on December 20, 2016, 06:41:27 PM
Hans,

I can take a picture of my setup this evening if you want to see it.  I have a full Proxxon kit that allows me to do pretty much anything I want.  I'm using the Proxxon MB 200 drill stand with a 12 volt rotary tool.  I added the KT 70 compound table, and it allows for very precise positioning.  The final piece I added is the MF 70 precision vise.  It's a bit spendy to get it all, but using these items I've been able to do all the precision drilling and milling required for my VP.  I've also started using my rotary tool at it's lowest speed to sand the carbon tubes down to size, and it's much faster than using a hand drill.  

Jake


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on December 25, 2016, 07:18:32 PM
Hi Jake,
I got the Proxxon drill press as you suggested. I also got a set of circuit board drills (the ones with a fat chuck) and promptly broke a .011 tip by accidentally dropping it down the hole in the base. I immediately ordered a half a dozen drill bits knowing the inevitable.

I tried making a Kang style vp with two carbon tabs for the screws on one side. It's a fair bit of effort to make one that's well overweight at .116g, but it looks respectable and the action is nice with a bit of .013" wire either side going through a carbon tube, underneath which I lashed the blade tubes with a small dab of zap a gap and tying thread. I've also had a go at my first ever spring. I suspect it's too strong compared to the Treger' with 5 turns of .009" wire.
Hans


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on December 27, 2016, 12:29:18 PM
Focus on making the mechanism strong and reliable.  Weight isn't much of a concern with the 1.4g models.  My first carbon prop is 85mg heavier than my normal balsa props, but I still need about 100mg of spacers/ballast to bring my model up to weight.

If you have an opportunity, do a bunch of test flights with that VP and see how it works.  You want it to be consistent.  The prop should change pitch at around the same time in every flight.  You also want to make sure it's robust and reliable.  If you discover any weak points, fix them in the second version.  I find building VP mechanisms to be an iterative process that might require several revisions to work out all the bugs and fine tune the assembly process.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on December 28, 2016, 04:53:40 PM
Thanks Jake,
"Iteration"... I totally agree with you. I want a vp that will take a bit of punishment. That's one of the motivations besides needing the initiation. I started this vp with the idea of it being fully carbon. I ordered a length of 0.7mm pultruded tube and a length of 0.28mm rod, but when I was using the 0.28mm I noticed it would kink rather easily, which is why I went back to using wire to suspend the blade tubes on. I found no issues of friction with the wire inside a carbon tube.

I also used cuts of a 0.25mm flat carbon I was given by Bob Bailey. I found I had to add small pieces of 0.25mm over the holes I had to drill for the screws, because otherwise the screws just wobbled. I've now ordered slightly thicker carbon tube and rod thinking perhaps it might make for some more rigidity. BTW: without the drill press I think it's next to impossible to drill those tiny holes without a degree of precision. I have ordered the vise, but I've been using a small piece of basswood as a surface with good results.
thanks again,
Hans


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on December 29, 2016, 03:44:17 PM
I'm planning to eventually submit a construction article to INAV, but here is a drawing for my current VP mechanism. 


Title: Re: VP Hubs - for the techies among us
Post by: dslusarc on December 29, 2016, 04:01:54 PM
Who is the source for the .08mm carbon for laminating on the yoke?


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on December 29, 2016, 04:50:08 PM
thanks for your drawing Jake. It would be brilliant if you offered some notes on your vp build.

I've made a yoke like the one in your illustration by gluing some .025 carbon around a balsa U shape as a potential Treger yoke replacement. It's rather heavy of course. I haven't tried the rohacel idea. From what I've gleaned you make two long U shapes over some form out of carbon prepreg, which you then glue (epoxy?) over a U shaped rohacel (presumably hot wired).

I was trying to avoid the yoke and go with two tabs on either side thinking it might be a bit tougher. I made the preload hole a little above the top stop hole, then played around with the spring to get it to work. I don't particularly like the fact that I had to "dog-leg" my spring downwards to meet up with pin holding plate.

Hans
ps: a good source for lightweight carbon prepreg this end of the pond is Roel at Creative Composite Technologies.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on December 29, 2016, 05:00:48 PM
Who is the source for the .08mm carbon for laminating on the yoke?

I got mine from Mike Woodhouse in the UK (freeflightsupplies.co.uk).  I just checked his site and right now he only lists 0.12mm material.  You could try emailing him and see if he has any of the 0.08 material left.  You can also get something very similar from CST in the US.  It's listed as 1.5 oz/yd^2 unidirectional carbon.  Both have binders to hold the fibers together, but the Russian material looks a little nicer in my opinion.  Either will work.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on December 29, 2016, 05:29:31 PM
From what I've gleaned you make two long U shapes over some form out of carbon prepreg, which you then glue (epoxy?) over a U shaped rohacel (presumably hot wired).

It's actually quite a bit different than your description.  I largely copied the method Brett Sanborn details in the 2012 NFFS symposium.  I did make a few changes to accommodate the tools I have available, and to accommodate the fact that I'm using a Foodsaver as my vacuum.  The channel is cut in the foam using an end mill in my Proxxon, and the final shaping is done with sandpaper.  I make my own prepreg by soaking the .08mm carbon in resin, and then placing it in a vacuum bag between layers of paper towel.  After 5 minutes sealed in the bag under vacuum I end up with around 30% resin content (I use this same method for pulling excess resin out of the tow I use for blade outlines) .  After that everything is assembled on the form (a piece of 3.2mm x 25mm x 150mm aluminum extrusion from the hardware store) and vacuum sealed in a bag until the resin is cured.  After curing I use the Proxxon with a small diamond blade to slice finished pieces at the correct width.

The next time I lay up an assembly I'll take photos and post a new thread with construction details.  In the meantime I would recommend getting a copy of that symposium.  It contains a wealth of knowledge about making composite hubs.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on December 30, 2016, 12:04:12 PM
Hi Jake,
Thanks. I believe that would require a purchase.
Is this the link you refer to? https://freeflight.org/product/nffs-symposia-2012/
Hans


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on December 30, 2016, 12:06:16 PM
Yes, you'll need to buy it.  They sometimes have used copies available for less, so it wouldn't hurt to email and ask.


Title: Re: VP Hubs - for the techies among us
Post by: dslusarc on December 30, 2016, 01:15:57 PM
Thanks for the info. Turns out I have that symposium and did not know it. I got a box of stuff from a friend who retired from modeling and there were some modeling books and a few symposiums :-) I have a foodsaver as well. Now I need to order some stuff and get this all figured out. 


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on December 30, 2016, 01:34:59 PM
thanks for your drawing Jake. It would be brilliant if you offered some notes on your vp build.

I've made a yoke like the one in your illustration by gluing some .025 carbon around a balsa U shape as a potential Treger yoke replacement. It's rather heavy of course. I haven't tried the rohacel idea. From what I've gleaned you make two long U shapes over some form out of carbon prepreg, which you then glue (epoxy?) over a U shaped rohacel (presumably hot wired).

I was trying to avoid the yoke and go with two tabs on either side thinking it might be a bit tougher. I made the preload hole a little above the top stop hole, then played around with the spring to get it to work. I don't particularly like the fact that I had to "dog-leg" my spring downwards to meet up with pin holding plate.

Hans
ps: a good source for lightweight carbon prepreg this end of the pond is Roel at Creative Composite Technologies.

I use carbon plate for the screw holder with the plate turned perpendicular to the prop spars. Not saying this is better or as light but it's a heck of a lot easier to make. It puts the strong axis of the screw holder in the direction of the loads from the screws. You can use blocks of balsa or bass glued to the carbon plate where the actual screws go.

See reply #115 if interested.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on December 30, 2016, 01:57:46 PM
Not saying this is better or as light but it's a heck of a lot easier to make.

I think the difficulty is relative.  That type of screw block is easier to make if you only want 2 or 3, but the composite screw blocks described here and in the 2012 symposium are much easier to batch out.  It takes me a couple hours to mold a 4" long piece of screw block, and after that I can slice 30 pieces to finished width in a few minutes.  At this point I've also created simple fixtures for every step of the process so I get consistent parts that are interchangeable rather than one offs.  My intention is to build multiple extra hubs that are all identical so if I have a problem with one, I can simply swap the blades onto a new hub and quickly get back to flying.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on December 30, 2016, 02:46:07 PM

See reply #115 if interested.
[/quote]

Thanks oldbill. I see your point(s). Everything about your vp looks tougher than mine. I'm curious whether the .011" rod over the .038" tube was to strengthen the tube due to the hole to accommodate the vertical tube. What MW did you use for your spring? It looks like 6 turns.

The top tube I tried to use is .027" (0.7mm), just too skinny to drill a hole through to accommodate a .025" hypodermic needle tube, so I lashed it on the side. I started off with the feeling that perhaps a tab either side might be a clever way around the U shaped yoke issue.
Hans


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on December 30, 2016, 03:06:04 PM
My hub is for F1M so it would need downsizing for F1D.

I set the hypo tube into a slot in the horizontal tube. The .011 rod was to close the slot.

Jake's method is better for serious F1D use. I build a hub every 2 or 3 years so mass production isn't an issue.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on December 30, 2016, 06:34:22 PM
From what I've gleaned you make two long U shapes over some form out of carbon prepreg, which you then glue (epoxy?) over a U shaped rohacel (presumably hot wired).

It's actually quite a bit different than your description.  I largely copied the method Brett Sanborn details in the 2012 NFFS symposium.  I did make a few changes to accommodate the tools I have available, and to accommodate the fact that I'm using a Foodsaver as my vacuum.  The channel is cut in the foam using an end mill in my Proxxon, and the final shaping is done with sandpaper.  I make my own prepreg by soaking the .08mm carbon in resin, and then placing it in a vacuum bag between layers of paper towel.  After 5 minutes sealed in the bag under vacuum I end up with around 30% resin content (I use this same method for pulling excess resin out of the tow I use for blade outlines) .  After that everything is assembled on the form (a piece of 3.2mm x 25mm x 150mm aluminum extrusion from the hardware store) and vacuum sealed in a bag until the resin is cured.  After curing I use the Proxxon with a small diamond blade to slice finished pieces at the correct width.

The next time I lay up an assembly I'll take photos and post a new thread with construction details.  In the meantime I would recommend getting a copy of that symposium.  It contains a wealth of knowledge about making composite hubs.

Hi Jake,
fascinating. Presumably your partially cured carbon is just flexible and perhaps not too tacky when you put it in the form and presumably you've applied a release agent to that first. Then you add the rohacel section and finally the last layer. I'm guessing you must have some sort of square rod to push the elements down before putting in the vacuum bag.
Hans


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on December 30, 2016, 07:48:05 PM
It would be difficult to explain the process without basically re-writing the entire several page article from the Symposium. 


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 01, 2017, 05:51:06 PM
fair enough. I've got some reading to do.

My first vp effort clearly leaves much to be desired. I installed a pair of blades in it and noticed poor spar alignment. Put the same blades in a Treger and there's not a hint of misalignment.
Hans


Title: Re: VP Hubs - for the techies among us
Post by: dslusarc on January 01, 2017, 10:25:13 PM
Thanks for the links on where to buy and how to do this. I have placed my order from CST for various things to try and make this with my food saver. This should be interesting :-)

Don


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 09, 2017, 06:48:10 PM
hi guys,
I'm on my third vp iteration using carbon and employing some of the tips and hints on this thread.  The total weight is .118g. I used three aluminium screws off an old Treger and I want to try to thread my own now. I think it's a case of threading some 1mm aluminium rod or wire and I have a die for it, but i have a feeling it might be hardened aluminium. Can anyone enlighten where one might find this?
cheers
Hans


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 09, 2017, 07:14:10 PM
I use 1mm aluminum tubing from the link below.  It's a delicate process that requires some practice.  You can only cut about 1/4 of a turn before backing out to break off the chip.  If you try to cut too much at once you'll break off the tube in the die.  Once you get a feel for it goes rather quick and I can cut a 15mm long piece in a few minutes.  From there I break the screws to length, mash one end to use as a head, file any burrs or sharp corners off the head, and file the other end flat.  All of that is done with the screw installed in a piece of 1.5mm thick brass plate with an M1 threaded hole.  I clamp the brass in a vise, and it allows me to work on the screw with both hands free.

http://store.spruebrothers.com/product_p/albat1m.htm


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 02:33:25 AM
I'm right in the middle of making several new VP hubs, so I snapped a few pictures tonight.  I made an album that gives a basic idea of how I make the screws.  The aluminum is held with a pin vise, and for now I clamp the die in a small bench vise.  Eventually I'd like to make something a little nicer to hold the die. 

The almost finished hub in this album weighs 71mg.  All I have left to do is drill a hole through the center of the screw block and glue a piece of 0.25mm carbon rod in it to pin the block in place.  This provides extra insurance to prevent the screw block from spinning on the center spar.  That should only add a couple milligrams so I would expect the finished hub weight to be under 75mg.  The driver pins will be attached to the ends of the spars, but if I add those in as part of the hub weight, it brings the total to 80mg.

https://goo.gl/photos/NfTGrTvXULDCp6Vj6


Title: Re: VP Hubs - for the techies among us
Post by: Tapio Linkosalo on January 10, 2017, 02:58:29 AM
Jake, your pitch fork looks really smart. How do you get them so well finished? Mine are always way more tatty when dremeled from the stock...


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 10, 2017, 08:13:14 AM
thanks for the info on the making of the screws Jake. Intriguing that you are using a tube! Treger's are solid rod with a slot in them, but I like what you are doing. The yoke is indeed a thing to behold. I was pleasantly surprised at my first attempt at making a spring with .008" wire. I did two failed attempts in which I was unwittingly overlapping the previous turns making a spiral mish-mash, then I got the hang of gently going upwards with the notched brass tube.I notice you have 8 turns, when I've gone for 5. Does 8 turns of the same thickness of wire make for a stronger spring? If you have any more photos of any of your vp making processes I would be delighted to scrutinise!
Hans


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on January 10, 2017, 10:07:21 AM
Treger might be envious!


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 11:28:32 AM
Jake, your pitch fork looks really smart. How do you get them so well finished? Mine are always way more tatty when dremeled from the stock...

To slice the screw blocks I turn the head on my Proxxon drill press stand to 90 degrees and lock the head in place.  I use a small diamond cut off wheel in the rotary tool, and I clamp a straight edge on my X-Y table running in the Y direction.  The screw block stock is then clamped in my small Proxxon vise with a couple centimeters sticking out one side.  I slide the edge of the vise against the straight edge to run the stock through the cut off wheel to get a square edge.  Then I move the table 2.2mm (1.7mm finished width plus 0.5mm blade kerf) in the X direction and slice off a piece.  After that it's just a repetitive process moving the table and slicing off screw blocks.  I cut about a dozen, and they were all within .02mm in width.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 11:55:18 AM
Does 8 turns of the same thickness of wire make for a stronger spring?

More turns will give a softer spring.  My understanding is that the softer the spring, the faster the prop will change pitch.  With my hub I haven't timed the changeover on a full motor, but on my 37.5% motors it took a little over 2 minutes to fully change pitch.  This would equate to around 6 minutes on a full motor.  I can't say if that's ideal, but test flights indicate my model should be capable of more than 25 minutes at West Baden, and more than 27 minutes at Kibbie.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 12:11:19 PM
Intriguing that you are using a tube! Treger's are solid rod with a slot in them, but I like what you are doing.

The idea for using an aluminum tube originally came from Kevin Lamers.  He got the Albion tubing at a local store and found that he could make screws with it.  Luckily I can get it in the US at the link I posted previously.

It takes some practice to get the process down, but once you get going it isn't all that difficult to make your own screws.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 10, 2017, 02:51:50 PM
Hi Jake,
Thanks. I've tracked the tubing here. With the name Albion that perhaps wasn't too surprising!
I'm using a jewellers frame saw and I'm curious what fret saw blades you are using for your carbon. I've been using Pebeco/Niqua blades, which are apparently great for wood marquetry. To my thinking the 1.7mm spacing between the teeth on mine is too wide and there's too much 'catching'.
Hans


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 03:29:53 PM
I'm using a jewellers frame saw and I'm curious what fret saw blades you are using for your carbon. I've been using Pebeco/Niqua blades, which are apparently great for wood marquetry. To my thinking the 1.7mm spacing between the teeth on mine is too wide and there's too much 'catching'.
Hans

I don't use a jeweler's saw for anything.  All of the carbon is cut with a diamond blade in my rotary tool, and the slot is cut in the driver with my Proxxon setup using a .013" diameter carbide end mill.  I mount a piece of scrap plywood to my X-Y table, and I use a 1mm diameter spiral bit to cut a 1mm wide by 0.4mm deep groove in the plywood.  I make the groove about 25mm long.  I cut the driver blanks to a rough length of about 20mm, and they're a press fit into the groove in the plywood.  I also use a little tape at each end to make sure the carbon doesn't lift or move.  Then I swap bits to the .013" end mill and use the X-Y table to precisely locate the holes and mill the slot.  I use the depth stop on the drill press stand to ensure that the bit is just deep enough to go all the way through the carbon.  When cutting the slot I plunge the bit into the carbon and lock the head in place using the set screw.  Then I move the table the proper distance and unlock the head to retract the bit out of the material.  The result is perfectly spaced holes, and a perfect slot.

Here's a link to the end mill I use.  I would recommend using the Proxxon collets rather than the 3 jaw chuck for this process.  The chuck is very good, but the collets run truer with less runout.

http://www.ebay.com/itm/1-KEO-013-X-039-x-1-8-Micro-2-FLUTE-CARBIDE-Square-END-MILL-83709-USA-NEW-/360490322278?hash=item53eee5c966


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 10, 2017, 04:05:29 PM
 I mount a piece of scrap plywood to my X-Y table, and I use a 1mm diameter spiral bit to cut a 1mm wide by 0.4mm deep groove in the plywood.  I make the groove about 25mm long.  I cut the driver blanks to a rough length of about 20mm, and they're a press fit into the groove in the plywood.  I also use a little tape at each end to make sure the carbon doesn't lift or move.  Then I swap bits to the .013" end mill and use the X-Y table to precisely locate the holes and mill the slot.  I use the depth stop on the drill press stand to ensure that the bit is just deep enough to go all the way through the carbon.  When cutting the slot I plunge the bit into the carbon and lock the head in place using the set screw.  Then I move the table the proper distance and unlock the head to retract the bit out of the material.  The result is perfectly spaced holes, and a perfect slot.

Given what you have that makes sense Jake.
To recap when you refer to X-Y table you are referring to this http://www.proxxon.com/en/micromot/27100.php or perhaps even this set up http://www.proxxon.com/en/micromot/27112.php#27114
At present I have this http://www.proxxon.com/en/micromot/28606.php
I'm not sure whether I could mount a compound table on to that. I think your set up is for the milling machine.
Hans


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 04:31:01 PM
Correct, I have the compound table mounted to the MB 200 drill press stand (http://www.proxxon.com/en/micromot/28600.php).  It will also mount to your drill press stand and includes the necessary hardware.


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on January 10, 2017, 05:24:06 PM
Correct, I have the compound table mounted to the MB 200 drill press stand (http://www.proxxon.com/en/micromot/28600.php).  It will also mount to your drill press stand and includes the necessary hardware.

There was a very nice article on the Dumore sensitive drill press in INAV recently. You can do much of the same work it and a microscope slide holder more cheaply than the Proxxon route.

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 10, 2017, 05:51:27 PM
Correct, I have the compound table mounted to the MB 200 drill press stand (http://www.proxxon.com/en/micromot/28600.php).  It will also mount to your drill press stand and includes the necessary hardware.

One thing I learned is that it's foolhardy to try to make a groove with my very nice drill bits I bought https://www.amazon.co.uk/dp/B01ILXNJDW/ref=pe_385721_51767431_TE_dp_1
they break almost instantly with sideways pressure. Presumably you must also be careful with the milling bits!

Thanks for the Dumore tip Mike! It looked at the INAV piece. It looks like a solid piece of kit, although the 110v is disadvantageous for me.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 05:56:59 PM
I saw that article and actually looked for a used Dumore.  Perhaps I have bad luck, but I've never seen one for under $200, and the ones available at that price are typically in pretty bad condition.  The Proxxon setup is probably slightly less precise, but the runout with a collet is less than I can measure and it's capable of 20,000 RPM.  I've also found the Proxxon to be more versatile because I can use it handheld as rotary tool, or rotate the drill stand 90 degrees and use a diamond cutoff blade to slice parts to precise length.  

Ultimately I think it depends on what you need, and what you can find.  The Proxxon setup I have is probably about $350, but I had a $100 gift card which is part of why I chose it.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 06:04:05 PM
One thing I learned is that it's foolhardy to try to make a groove with my very nice drill bits I bought https://www.amazon.co.uk/dp/B01ILXNJDW/ref=pe_385721_51767431_TE_dp_1
they break almost instantly with sideways pressure. Presumably you must also be careful with the milling bits!

Drill bits are designed only to bore holes.  Any side load and they'll break as the carbide is quite brittle.  End mills on the other hand are specifically designed for milling slots.  You can still break an end mill if you feed the material too fast, but I'm still on my first one after cutting about a dozen drivers arms.


Title: Re: VP Hubs - for the techies among us
Post by: dslusarc on January 10, 2017, 07:07:23 PM
Jake,

Thanks for posting all this info. I have been buying as links get posted. My carbon arrived form CST. Ordered the tubing and end mills today.

So to make a mill setup this is what I would need to buy correct?

Precision Rotary Tool FBS 115/E or Professional Rotary Tool IBS/E
Drill Stand MB 200
MICRO Compound Table KT 70

Or do I go for the whole mill: MICRO Mill MF 70

Any other suggested accessories or holder I might need?

Don


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on January 10, 2017, 07:30:29 PM
I saw that article and actually looked for a used Dumore.  Perhaps I have bad luck, but I've never seen one for under $200, and the ones available at that price are typically in pretty bad condition.  The Proxxon setup is probably slightly less precise, but the runout with a collet is less than I can measure and it's capable of 20,000 RPM.  I've also found the Proxxon to be more versatile because I can use it handheld as rotary tool, or rotate the drill stand 90 degrees and use a diamond cutoff blade to slice parts to precise length.  

Ultimately I think it depends on what you need, and what you can find.  The Proxxon setup I have is probably about $350, but I had a $100 gift card which is part of why I chose it.

Hi Jake.

It is sort of hit or miss unless you decide to take your time. $200-$250 is the range typically for one in decent shape. You can still get bearings for them too, so no worries there.
(I have a contact if you need it.)

The Proxxon looks like a very nice unit as well. Me, if the Dumore can't do what I want, I just head to the local Maker space and use their Bridgeport.  :)

Regards.
Mike Kirda



Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 08:37:46 PM
Jake,

Thanks for posting all this info. I have been buying as links get posted. My carbon arrived form CST. Ordered the tubing and end mills today.

So to make a mill setup this is what I would need to buy correct?

Precision Rotary Tool FBS 115/E or Professional Rotary Tool IBS/E
Drill Stand MB 200
MICRO Compound Table KT 70

Or do I go for the whole mill: MICRO Mill MF 70

Any other suggested accessories or holder I might need?

Don

Don,

It really depends on your needs and goals.  I bought the Proxxon 50 EF rotary tool and the NG 2/S transformer from a local woodworking store because I had a gift card.  After that I went down a rabbit hole and bought a bunch of accessories.  Ultimately the setup I have works, but it is a compromise.  The MF 70 is likely nicer and easier to use for most of the parts necessary to make a VP similar to mine, but I've never used it. 


Title: Re: VP Hubs - for the techies among us
Post by: dslusarc on January 10, 2017, 10:17:01 PM
Well I decided to buy the mill and the precision vise for it. Guess I will have no more reasons to not make one of these carbon VP hubs eh  ;D

Don


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 10, 2017, 11:47:29 PM
Well I decided to buy the mill and the precision vise for it. Guess I will have no more reasons to not make one of these carbon VP hubs eh  ;D

Don

I'll be curious to hear what you think of it.  Some day I'd like to get one myself.  I also found a whole bunch of CNC conversion kits that exist for it including a couple that you can 3D print.  You can get the electronics and hardware for under $100, and it would open up some interesting possibilities.

http://www.thingiverse.com/thing:21890


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 12, 2017, 11:34:42 AM
I added more photos to the photo album I linked in reply 170.  It includes photos of the finished prop which ended up at 300mg.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 13, 2017, 11:39:18 AM
impressive work, Jake. Now you're making me wonder about a carbon outline! Is it possible to make those with single strands of Mike Woodhouse's Russian carbon cloth and the Zpoxy finishing resin? I imagine if you have a fibreglass template made from a prop block you can cut a groove in the end of that and layup the fibres. I'm having a go as we speak on the aluminium screws on the 1mm tube. It's very easy to break the tips off! I'm going to try with a bit of lube.


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on January 13, 2017, 11:48:03 AM
impressive work, Jake. Now you're making me wonder about a carbon outline! Is it possible to make those with single strands of Mike Woodhouse's Russian carbon cloth and the Zpoxy finishing resin? I imagine if you have a fibreglass template made from a prop block you can cut a groove in the end of that and layup the fibres. I'm having a go as we speak on the aluminium screws on the 1mm tube. It's very easy to break the tips off! I'm going to try with a bit of lube.

Double that tow to the first rib at least, otherwise you will get significant flex on the inner portion.

I've built one but not flown it yet. I will rebuild it as above though for that reason.

Mike


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 13, 2017, 11:56:56 AM
Mike: what did your outline weigh, and what do you estimate for version 2?


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on January 13, 2017, 11:58:39 AM
Mike: what did your outline weigh, and what do you estimate for version 2?

I don't recall offhand. Maybe I'll make one this weekend and get back to you.

Mike


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 13, 2017, 12:11:00 PM
Is it possible to make those with single strands of Mike Woodhouse's Russian carbon cloth and the Zpoxy finishing resin?

I think this is a risk because we have no idea what carbon is in that Russian cloth.  Not all carbon fiber is equal, and you need something with high modulus so it doesn't flex too much.  If you want more information on molding blades, you need to read Brett Sanborn's article on INAV.  It's incredibly thorough, and he even gives a detailed explanation of why most types of carbon fiber won't work for blade outlines.

https://indoornewsandviews.com/2013/04/05/carbon-prop-outlines-brett-sanborn/


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 13, 2017, 12:22:36 PM
Brett also wrote a follow up linked below.  I'm using the EZ-Lam 60 he mentions in this article.  It's very inexpensive when compared with most of other composite resin.  I've been curing for 24 hours at 90F and it seems to work well.

https://indoornewsandviews.com/2013/06/25/carbon-prop-outline-follow-up/


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on January 13, 2017, 12:24:02 PM
Is it possible to make those with single strands of Mike Woodhouse's Russian carbon cloth and the Zpoxy finishing resin?

I think this is a risk because we have no idea what carbon is in that Russian cloth.  Not all carbon fiber is equal, and you need something with high modulus so it doesn't flex too much.  If you want more information on molding blades, you need to read Brett Sanborn's article on INAV.  It's incredibly thorough, and he even gives a detailed explanation of why most types of carbon fiber won't work for blade outlines.

https://indoornewsandviews.com/2013/04/05/carbon-prop-outlines-brett-sanborn/

Depends upon what you are looking for, Jake. If you use a balsa spar/ribs, but ditch the 0.025" square balsa outline for the carbon one, the carbon one is less likely to break.

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 13, 2017, 12:37:47 PM
Depends upon what you are looking for, Jake. If you use a balsa spar/ribs, but ditch the 0.025" square balsa outline for the carbon one, the carbon one is less likely to break.

Regards.
Mike Kirda

If you're saying build a traditional prop with a full length spar, but replace the balsa outline with carbon then I'm not sure I understand the point.  The carbon outline will be significantly heavier than balsa, but you don't get the advantage of reduced drag by removing most of the spar.  I've never had an issue with breaking balsa prop outlines.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 13, 2017, 05:55:46 PM
going back to the subject of vp: my third version has a carbon rod on which hang my fibreglass prop blade tubes. The rod in turn runs through a carbon tube. It seems very smooth in terms of action. But what I've been reading from your experience and Kang's, it would appear friction is an issue, I guess under load. You talk about teflon dust... is a bit of lube out of the question?


Title: Re: VP Hubs - for the techies among us
Post by: mkirda on January 13, 2017, 06:06:42 PM
going back to the subject of vp: my third version has a carbon rod on which hang my fibreglass prop blade tubes. The rod in turn runs through a carbon tube. It seems very smooth in terms of action. But what I've been reading from your experience and Kang's, it would appear friction is an issue, I guess under load. You talk about teflon dust... is a bit of lube out of the question?

I have used silicon o-ring lube from an old Nikonos I have. It works great, no binding. I also smooth the 0.020" rod with 2500 grit sandpaper first.

Regards.
Mike Kirda


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 13, 2017, 06:07:05 PM
I built a prototype hub a few years ago using Kang's design as a reference, but I never added blades and actually flew with it.  I know Kang had issues with friction, but I'm not sure if he resolved them.  I haven't seen any of his VP hubs in quite a while so I don't know if he's still using that design, or abandoned it for something else.  

For what it's worth, I haven't had any issues with friction in my hub design which also involves carbon on carbon.  I initially used PTFE powder, but I've since abandoned it as I don't think it's necessary.


Title: Re: VP Hubs - for the techies among us
Post by: dslusarc on January 13, 2017, 10:54:55 PM
UPS brough me a box today. Nice piece of equipment. Now to find a feed rate for carbon fiber. How many end mills will I break?  ;D


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 14, 2017, 02:19:30 PM
UPS brough me a box today. Nice piece of equipment. Now to find a feed rate for carbon fiber. How many end mills will I break?  ;D
nice one! I bought a kt 70 base for my drill stand (MB 140) and a milling bit today. There's going to be some carbon dust flying about both sides of the pond I think.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 21, 2017, 11:53:10 AM
I had a go at flying my vp for the first time. I discovered that my spring is too weak right off the bat and that my top hat slips off the top stop screw! Still performance wasn't bad at all, once I got the blade angles reasonably close.


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on January 21, 2017, 01:48:46 PM
my top hat slips off the top stop screw!

I've seen some very competent fliers have this problem. For my F1M hubs I nearly always add a carbon shim to thicken the arm where it hits the high pitch screw (and possibly the low pitch screw also).


Title: Re: VP Hubs - for the techies among us
Post by: Olbill on January 21, 2017, 07:31:24 PM
This is maybe off topic but I just bought a new cordless Dremel tool - a model 8220. My old Model 800 died for the second or third time so I decided it was time to move on. The Model 8220 is a lot bigger and heavier - 23 ounces vs. 16. I'm hoping it's going to be a good replacement for the old one.

And of course the battery is different.


Title: Re: VP Hubs - for the techies among us
Post by: brabazon on January 22, 2017, 10:02:56 AM
my top hat slips off the top stop screw!

I've seen some very competent fliers have this problem. For my F1M hubs I nearly always add a carbon shim to thicken the arm where it hits the high pitch screw (and possibly the low pitch screw also).

yes, that's a good suggestion. I might also mush the end of the aluminium screw head to make it more pan shaped.


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on January 25, 2017, 03:18:24 PM
For anyone that wants more information on my VP hub, a construction article with some photos was just published on INAV.

https://indoornewsandviews.com/2017/01/25/the-almost-all-carbon-f1d-vp/


Title: Re: VP Hubs - for the techies among us
Post by: Skymon on February 28, 2018, 08:31:14 AM
Jake
Massive respect to you for cutting threads on that ally tube!!!
I've been struggling and struggling :(
When you say 'take it slow' wow, you really mean it :)
S


Title: Re: VP Hubs - for the techies among us
Post by: jakepF1D on February 28, 2018, 11:57:00 PM
It does take a lot of patience and practice, but it gets easier.  I've done enough of them now that it's become fairly easy, but I spent a lot of time cleaning aluminum chunks out of my thread die when I started.


Title: Re: VP Hubs - for the techies among us
Post by: Skymon on March 01, 2018, 03:20:16 AM
Me too  ;D
I struggle with the patience required to perform 1/8th of a turn, then back off.
I started using a 4" rod and quickly moved on to your advised tiny stub in a pin vice.
Thanks so much for sharing your methods.
I love the collaboration in this hobby.

Best regards
S