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Old 08-29-2017, 06:20 AM   #1 (permalink)
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Default Having trouble with an aileron wobble

My 3digi is on a heli i built myself, and I've been struggling to get the aileron gyro to behave nicely.

Is it unusual to have the aileron gain at less than 1/2 of the elevator gain?

I have elevator and aileron overall gains on trimmer switches on my A9x radio. In flight, I can change the aileron gain from 60 down to less than 40 but the wobble stays pretty much the same. going higher than 60 makes it shake hard. Stability seems to improve as I increase the head speed but I'm up to 2400rpm now and I don't want to go faster.

The elevator overall gain is at 80 and holds well.

I've tried putting shorter, stiffer servo horns on it but that didn't have any effect.
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Old 08-29-2017, 06:22 AM   #2 (permalink)
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Default Hmm...

While typing that previous post and playing with the terminal on pc, I realise I probably should have had P gain on the trims, not overall gain? Can I reset gains to default without resetting all configuration settings? I'm a bit lost now, I think I've changed to many things
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Old 08-29-2017, 06:32 AM   #3 (permalink)
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Not sure which it is since I've always avoided fbl that use PID for tuning. On my Skookum it would be a cyclic gain adjustment that cures cyclic wobble so whichever translates to that will be the one you want.

Also check blade balance and look for slop in the head and main gear assemblies which can also cause cyclic wobble. Usually slop between the spindle shaft and dampers for aileron wobbles/shakes

Most of the newer helis have high mechanical gain so low gain values in the fbl are nothing to worry about especially if it's smaller than 500 class
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Old 08-29-2017, 06:47 AM   #4 (permalink)
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I had 2 sk540s, I sold one and retired the other one. I used to love them but after flying some of the more modern gyros, I could never get the feel I wanted from the skookums. Eznov, 3digi, even the Kbar all seem to feel nicer. I could never put my finger on the difference, which made it very hard to chase the tune.

Regarding my current issue, I hit reset and am now doing a fresh setup.
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Old 09-09-2017, 08:30 PM   #5 (permalink)
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Default cyclic wobble

mine has the same problem, adjsted everything i could imagine in aileron,swash gains. no change. its like a harmonic issue or something. could it be the mounting of the 3 digi i used vzb or whatever it is the 3m red backed tape..
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Old 09-09-2017, 08:31 PM   #6 (permalink)
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Default cyclic wobble

mine has the same problem, adjusted everything i could imagine in aileron,swash gains. no change. its like a harmonic issue or something. could it be the mounting of the 3 digi i used vzb or whatever it is the 3m red backed tape..
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Old 09-10-2017, 03:52 AM   #7 (permalink)
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I don't think that it's a mounting problem of the 3Digi.
Is the issue only at a certain RPM?

If reducing gains doesn't help then it's obviously a mechanical problem.
Check your rotorhead (bearings and damping) and maybe try to change the damping or your rotor RPM a little bit up or down. Maybe you leave the harmonic range then.
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Old 09-10-2017, 06:11 PM   #8 (permalink)
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Quote:
Originally Posted by DirkS View Post
I don't think that it's a mounting problem of the 3Digi.
Is the issue only at a certain RPM?

If reducing gains doesn't help then it's obviously a mechanical problem.
Check your rotorhead (bearings and damping) and maybe try to change the damping or your rotor RPM a little bit up or down. Maybe you leave the harmonic range then.
i have now tried moving balls in/ out, and many gain settings and it only smooths out if i lower the aileron/elevator gain to about 30 or below.. and feels loose then. i did try different rpms for harmonics and it helped a little but i still cant narrow it down. my other 3 digis dont do this but they are on different helis. this one that shakes is on a agile 7.2. it is smooth as silk until it shakes so i dont think anything is bent or wierd mechanically. not sure. i tried different sets of blades also.. same results
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Old 09-11-2017, 02:47 PM   #9 (permalink)
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How far away are you from the standard settings? Maybe try to make the step back and start from the beginning.
If it is a fast shake, try to reduce P only. The remaining I helps that the heli doesn't feel too loose.
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Old 09-11-2017, 08:39 PM   #10 (permalink)
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i will try again tommorow. i have changed shims in my feathering shaft now also which seemed a little tight horizontally. so i put smaller shims to loosen the head pinch and lubed it better.. i compared it to my other agile 7.2 and that is the major difference in the 2 heads is the shimming... i will report back.. it may not be as much to do with 3digi hopefully after all... if shaking is gone i will raise gains to see if it is gone throughout.. thanks Dirk..
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Old 09-12-2017, 08:39 AM   #11 (permalink)
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I changed my 623mm blades to 600mm and set my head speed up another 50rpm to 2450rpm. I can run twice as much aileron gain now! It still gets a bit of a wobble occasionally when hovering. The heli flies way better with the higher gain.

I also had a bit of elevator nodding when hovering at around 1800rpm. I suspect the head dampers are to stiff. I have some Align greys on the way, I'll report back when I've tried them.

Interestingly, the blades I'm using now are an old pair of thunder tigers that I had given up on years ago. They came in the kit with my X50 nitro. Running at about 2250rpm with SK540 it wobbled its guts out, unflyable. Align blades fixed that one.
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Old 09-13-2017, 06:37 PM   #12 (permalink)
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Default wobble

mine is still wobbling , it is better with softer align dampers i tried now but its not gone totally yet. im using about 40 ail. elev. gain..
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Old 09-17-2017, 03:28 AM   #13 (permalink)
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I flew with align grey dampers today. The aileron wobble is almost gone. Low head speed elevator nodding is fixed.

I'd like to try align red dampers but I'm scared of boom strikes. The red ones are very soft.

I think more head speed is the answer. My heli just seems to be unhappy around 2300 - 2400rpm, which is irritating as that's where I'd prefer it to be.

Is going up to 2500rpm wise? It'll probably eat up batteries a lot faster.
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Old 09-19-2017, 01:35 PM   #14 (permalink)
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How flexible are your landing gear ? Like rubbery? Or stiff
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Old 09-20-2017, 05:32 AM   #15 (permalink)
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I'm using align landing gear, its pretty stiff. My helis centre of gravity is quite close to the rotor disk. CG is almost exactly inline with the tail boom, and I use a short mainshaft.

I got some halo 610 blades today, I'll try em out tomorrow hopefully.
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Old 09-21-2017, 11:20 AM   #16 (permalink)
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Cool, just trying to narrow things down. It's like certain main shaft lenghts and flex play a roll in the harmonics that contribute to the headshake.. frame flex, dampers , etc..
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Old 09-24-2017, 09:00 PM   #17 (permalink)
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I had an aileron shiver on my Rush 750 that turned out to be tail/aileron interaction. Lowering the tail gain from 80 to 70 fixed it. I just added some extra stop gain to keep the piro stops sharp.
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Old 10-03-2017, 10:56 PM   #18 (permalink)
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Grey dampers, lubricated with silicon oil and halo 610 blades @2300rpm seems to be the sweet spot for me. All gains on 600 defaults except for ail/ele P which I have both set significantly higher. No wobble anymore flying really nice to!
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Old 10-07-2017, 11:08 PM   #19 (permalink)
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i found mine to be the motor belt tension after trying every other thing immaginable.. i just loosened the motor belt enough to get a small amount of deflection and the head shakes went away.. apparently a over- tight belt causes a vibration from the pull from the motor and tension..
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