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Author Topic: VP Hubs - for the techies among us  (Read 20342 times)
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jakepF1D
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« Reply #150 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.
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brabazon
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« Reply #151 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
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jakepF1D
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« Reply #152 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. 
Attached files Thumbnail(s):
Re: VP Hubs - for the techies among us
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dslusarc
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« Reply #153 on: December 29, 2016, 04:01:54 PM »

Who is the source for the .08mm carbon for laminating on the yoke?
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brabazon
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« Reply #154 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.
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jakepF1D
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« Reply #155 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.
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jakepF1D
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« Reply #156 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.
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brabazon
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« Reply #157 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
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jakepF1D
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« Reply #158 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.
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dslusarc
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« Reply #159 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. 
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Olbill
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« Reply #160 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.
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jakepF1D
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« Reply #161 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.
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brabazon
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« Reply #162 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
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Olbill
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« Reply #163 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.
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brabazon
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« Reply #164 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
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jakepF1D
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« Reply #165 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. 
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brabazon
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« Reply #166 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
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dslusarc
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« Reply #167 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
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brabazon
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« Reply #168 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
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jakepF1D
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« Reply #169 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
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jakepF1D
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« Reply #170 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
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Tapio Linkosalo
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« Reply #171 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...
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brabazon
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« Reply #172 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
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Olbill
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« Reply #173 on: January 10, 2017, 10:07:21 AM »

Treger might be envious!
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jakepF1D
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« Reply #174 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.
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