Helicopters C

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Rêveur
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Re: Helicopters C

Post by Rêveur » January 5th, 2018, 1:23 am

JasperKota wrote:
Rêveur wrote:Hi all.

I had a couple of questions regarding the rubber motors and winding. I'm having increasingly frustrating problems with my rubber motors breaking after being used only one or twice

Right now I'm using a 15:1 winder to wind my rubber. I am seeing other teams use 10:1 geared winders, however. Is there a significant benefit to using a smaller geared ratio? Possibly something about winding the rubber more slowly?

I'm also confused as to what lubricant to use. I've bought the "Armor All Original Protectant" but I suspect it might be eating away at my rubber motors, which only seem to last one or two flights before breaking. Can anyone give me any advice on this?
How much are you winding? Are you stretch winding?
DoctaDave wrote: The rubber should also be stretched at LEAST 7 times is original length when winding, but stretching out even longer will help you pack in turns tighter, especially after you have wound the motor 3-5 times...
I've used Armor All Original Protectant and it has worked very well for me, also make sure you're re-lubricating after each hard wind flight.
Hi Jasper,

I've been winding to around 55-60 on a 15:1 winder so about 825-900 winds. My partner and I stretch to about 4 times the original length as suggested in the FFM manual. We'll try 7 times the original length, though thinking about it now is scary as I'm not sure the rubber can take that much.

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Re: Helicopters C

Post by vjindal » January 5th, 2018, 5:28 am

Unome wrote:
vjindal wrote:
retired1 wrote:Dave is taking preorders at this time by email only for delivery in about a month. His website will not be up until the end of Oct or early Nov.

His helicopter is a Sikorsky in the fact that it has 2 rotors that are not coaxial. It is a wild design! Both rotors are pushers. The rotors should be easier to build this year, but the kit has a good bit of "cables" which some might have a bit of a problem with. He told me that he has had 2:30 times in an 8 foot ceiling and that it is very stable.
Each rotor has its own rubber band. My thought is that it will either take 2 torque meters, or one with a board to transfer the wound motor to until it can be loaded on the chopper. It will be interesting to see what his instructions have to say.
Is that 2:30 after the bonus (1 min actual time)?
Probably 2:30 pre-bonus, based on some of the flights by people using his kit. After the bonus, scores are reaching 6 minutes or more.
Wow, that's really impressive! What teams have been getting those times?
2019:
Mousetrap
Wright Stuff
Sounds

MIT 2018:
Heli: 1st
Mousetrap: 6th

--- Helicopters --- https://youtu.be/nn-x44gB0oA
--- Robot Arm --- https://www.youtube.com/watch?v=gmHcG-bar7w&t=76s
--- Wind Power --- https://www.youtube.com/watch?v=603F7vPUbrg&t=34s

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Re: Helicopters C

Post by coachchuckaahs » January 5th, 2018, 8:52 am

I agree with Dave, stretch at least 7x. Our students typically stretch to 8x. Hold full stretch to about half of your goal winds, you will feel a sudden increase in the pull. When you feel this, "follow the pull", or if using a torque meter, walk in while turning to keep same torque as when pull increased. About halfway in you should have well over 3/4 of your total winds.The torque will rise rapidly near the end, and walk in is much faster. Too fast on walk-in and you will have big knots.

The number of winds will depend on the width and length of your rubber. Keep careful notes! (logbook). Wind a small sample of your rubber width using this method, but wind to breaking (while walking in). Then proportion the number of winds to your actual length, and use maybe 90% of this number as a goal. Better yet, observe torque at which it breaks, and use torque meter to avoid breakage on same thickness rubber.

Wound this way, the peak torque will be quite high. You will want to back off to a suitable torque that your heli can stand on launch. Wind full,, then back down, do not just wind up to goal torque. This will put a lot more energy in the rubber (hysteresis).

Always wind OFF the heli, on a stooge, preferably with a torque meter. This will help avoid damage if the rubber breaks.

If you are really pushing the rubber, 2-4 flights may be all you get. If you are kinder (during practice), you may get 6-10 flights. You have to know the limits (where it breaks) to know how much is kind, contest-rough, and dangerous. Both torque and winds. With chinook, you also need torque to know that both rotors are wound equally.

Coach Chuck
Coach, Albuquerque Area Home Schoolers Flying Events
Nationals Results:
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records

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Re: Helicopters C

Post by Rêveur » January 5th, 2018, 10:16 am

coachchuckaahs wrote:I agree with Dave, stretch at least 7x. Our students typically stretch to 8x. Hold full stretch to about half of your goal winds, you will feel a sudden increase in the pull. When you feel this, "follow the pull", or if using a torque meter, walk in while turning to keep same torque as when pull increased. About halfway in you should have well over 3/4 of your total winds.The torque will rise rapidly near the end, and walk in is much faster. Too fast on walk-in and you will have big knots.

The number of winds will depend on the width and length of your rubber. Keep careful notes! (logbook). Wind a small sample of your rubber width using this method, but wind to breaking (while walking in). Then proportion the number of winds to your actual length, and use maybe 90% of this number as a goal. Better yet, observe torque at which it breaks, and use torque meter to avoid breakage on same thickness rubber.

Wound this way, the peak torque will be quite high. You will want to back off to a suitable torque that your heli can stand on launch. Wind full,, then back down, do not just wind up to goal torque. This will put a lot more energy in the rubber (hysteresis).

Always wind OFF the heli, on a stooge, preferably with a torque meter. This will help avoid damage if the rubber breaks.

If you are really pushing the rubber, 2-4 flights may be all you get. If you are kinder (during practice), you may get 6-10 flights. You have to know the limits (where it breaks) to know how much is kind, contest-rough, and dangerous. Both torque and winds. With chinook, you also need torque to know that both rotors are wound equally.

Coach Chuck
Thanks for your advice Chuck!

Interesting to see that you might only get 2-4 flights out of a set of rubber motors if we push the rubber to it's max. It was concerning a bit because I have done Wright Stuff in the past, and I remember reusing the same rubber motor up to 10 or 20 times. Looks like we'll be burning through a lot more rubber.
I'm seeing another problem that the O-rings provided in the FFM kit are the points of breakage in the rubber, as they seem to "pinch" the motor when wound creaking little micro-tears in the rubber structure. Does anyone know a solution for this?

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Re: Helicopters C

Post by Alke » January 6th, 2018, 9:41 am

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Re: Helicopters C

Post by Duckman » January 9th, 2018, 9:29 pm

Wabbit wrote:So, I've been doing helicopters for two years now and have gone through numerous iterations of my own designs, yet I feel like I must be missing some fundamental piece of the puzzle and was hoping someone here could help me out.

For context, my state banned the use of kits this year. I'm generally in support of the policy, since, at least to me, the thing that makes helicopters fun is coming up with your own designs. This means that getting one of the Freedom Flight Models kits is off the table for me as an option, but since the ban isn't in effect for most of the country, it can be hard to find solid advice on how to build a good helicopter from scratch.

Feeling like it would be too difficult to build a chinook, especially without a kit or set of plans to go off of, and knowing that other teams in my state also will have trouble utilizing the bonus due to the ban, I decided to go with a more standard design this year. So far, despite getting my helicopter to be super lightweight (just over 3.0 g), I haven't been able to do much better than about 45-50 second flight times. The most obvious reason for this is that I haven't been able to put more than roughly 300 total winds in my motor. This is an obvious difference between my design and some of the better ones from last year which, if I'm not mistaken, were using upwards of 1500 winds. The other main difference between my designs and objectively better ones is that my frame is significantly shorter, probably only about 30 cm long instead of what appeared to be closer to 90 cm long frames that were being used by the kits from last year.

So, then, the fix should be obvious to me, right? I make a much longer frame which allows me to use a much longer rubber band thereby allowing me to put in many more winds. But this hasn't worked. Every time I try to go with a longer rubber band, a larger frame, or both, I end up getting much shorter flight times. I would imagine this is due to the helicopter as a whole weighing significantly more. Even if I manage to keep the frame lightweight, the added length of the rubber motor makes the whole thing a lot heavier. I've experimented with every possible combination of sizes, and, using my current rotors, the thing that has worked the best is a super small frame with a relatively short rubber band. But I know from seeing other teams at competitions that this sort of design isn't supposed to yield good results, nor has it yet been able to replicate the times of even moderately good teams.

So I guess my question is, what were the kits from last year doing differently? How was it that they were able to use such a long rubber motor and such a large frame without the whole thing weighing way too much?

Thanks for your help!
Question: Is your state Massachusetts by any chance?

Last year I received 1st place in Massachusetts without Dave Zeigler's kit. This is because the event coordinator placed a significant penalty on all teams that flew the kit with its Carbon Fiber and Kevlar. My design looked somewhat similar to Mr.Zeigler's (great guy btw). My time was about 63 seconds without any bonuses. If you are interested I can dig it up and try to send you a picture it is a coaxial design.

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Re: Helicopters C

Post by coachchuckaahs » January 10th, 2018, 8:43 am

I am puzzled as to how a EC can apply a penalty in a purely timed event? Were teams tiered if they used a kit? What if they used carbon and kevlar, but it was not a kit?

The rules clearly allow a kit, and the only prohibited material is boron fiber. I suppose a Regional or State even could advertise in advance that kits will be tiered, but how could an EC "penalize" kits or materials that fit the rules?

We built last year without a kit, as our Regions and States are early (January and February), so we need to build before kits are available. However, we did utilize carbon and kevlar in order to make minimum weight. With axial heli's at minimum weight, the designs tend to look similar, with carbon spars, and carbon reinforcement or kevlar rigging on the motor stick.

This year, with the large bonus for Chinook, there is perhaps more room for design variations. However, Dave has something working nicely, and the overall layout of competitive designs may end up being very similar. With Dave's success, it is hard to start without a kit, though once a kit is built, perhaps you can look at design variations for improvements or personal touch. We again had to build without a kit due to timing, but were our Regions later in the year I woudl probably have started my kids with a kit.

Coach Chuck
Coach, Albuquerque Area Home Schoolers Flying Events
Nationals Results:
2016 C WS 8th place
2018 B WS 2nd place
2018 C Heli Champion
2019 B ELG 3rd place
2019 C WS Champion
AMA Results: 3 AAHS members qualify for US Jr Team in F1D, 4 new youth senior records

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Re: Helicopters C

Post by parikhy » January 10th, 2018, 2:09 pm

On the topic of kits, how many times do you wind total with the latest freedom flight kits? I'm trying to get to 35 feet. Considering ceiling heights and all, my event will not be taking place in the gym. I have read the previous comments about winding.

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Re: Helicopters C

Post by retired1 » January 10th, 2018, 2:36 pm

Rubber varies quite a bit, even in the same lot or spool, so you really need to do some testing to find out the breaking point. The FF chopper is fairly strong as far as the main motor booms go, so I do not think that you will have a problem with too much power with the smaller rubber provided. As he says, if it breaks, get out the CA glue (and hardener if you need it right now).
Old information that used to work fairly close was 1/8" rubber would take 106 turns per inch of use-able band. For 0.100 rubber, I would expect about 115 turns per inch to the breaking point. This is with a pre stretched band and a start wind distance of 6-7 vs the 4 recommended.
A torque meter will give you a world of valuable information about the breaking point and flights will tell you if you need to dewind a bit.
It is getting a bit late to do much testing with rotor pitch.
I assume that everyone is using a pitch gauge to insure that both blades on both rotors are the same.

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Re: Helicopters C

Post by parikhy » January 10th, 2018, 2:40 pm

This is going to sound crazy, but any advice on hand cranking? Anyone have any tips or know how to build a winder? I don't think I will have one by the time regionals comes around, although I am doing my best to try and get my hands on one.

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