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Author Topic: VP Hubs - for the techies among us  (Read 20843 times)
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leop
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« Reply #100 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
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Tapio Linkosalo
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« Reply #101 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....   
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Tapio Linkosalo
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« Reply #102 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!

 
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mkirda
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« Reply #103 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
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Tapio Linkosalo
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« Reply #104 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.

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Tapio Linkosalo
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« Reply #105 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....

   
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Tapio Linkosalo
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« Reply #106 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%.
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abdee1983
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« Reply #107 on: July 04, 2014, 04:44:29 AM »

oh..very good planes
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Olbill
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« Reply #108 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.
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mkirda
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« Reply #109 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
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Olbill
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« Reply #110 on: July 30, 2014, 09:40:10 PM »

Wire!

Oh - 5 turns of .013".
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Maxout
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« Reply #111 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!
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Olbill
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« Reply #112 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.
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jakepF1D
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« Reply #113 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.
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Olbill
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« Reply #114 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.
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Olbill
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« Reply #115 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!
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Tapio Linkosalo
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« Reply #116 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.


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Olbill
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« Reply #117 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.
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Tapio Linkosalo
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« Reply #118 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.

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Maxout
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« Reply #119 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.
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Tapio Linkosalo
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« Reply #120 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.


  
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ykleetx
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« Reply #121 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.
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Olbill
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« Reply #122 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.
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Tapio Linkosalo
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« Reply #123 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
 
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Maxout
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« Reply #124 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.
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