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Old May 27, 2011, 07:46 PM
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Walkera V450 shimmying problem, video in post

I recently crashed my v450 which bent the feathering shaft on one side........Following is a list of what I've checked so far so hopefully someone can help me figure out whats causing my shimmying problem because I'm stumped...keep in mind I'm fairly new to helicopters and this is my first CP machine. It worked perfectly when I got it from Wowhobbies untill this first crash which involved me practicing nose in about 5 feet high and a crash sideways into the ground when I lost orientation...a blade hit the ground first which bent the feathering shaft (somehow the blades survived unscathed)

- replaced bent feathering shaft

- new main gear, half the teeth were ripped off of the old one in the crash.

- replaced main shaft just in case although the old one doesn't appear to be tweaked at all.

-I replaced one grip tie rod that was lost somewhere in my front yard in the crash.

- I have the tracking pretty much perfect I believe, at least I adjusted the tie rods untill I could not distinguish one blade from the other when looking side on and spinning, per some instructional videos I watched.

- the tail boom was skewed slightly left ( maybe 3/8" ) in the crash but I was able to straighten it back up with a little pressure and it seems to be working fine. I don't see that causing this shimmying but I could be wrong.

- I checked the blades and they both weigh within 1/2 gram of each other according to my scales, the CG is also in the same spot on both.

Could a slightly tweaked grip be the problem?, they both look fine to my eye but how can you really tell for sure short of replacing both of them?

Maybe I don't fully understand this but when adjusting the two grip tie rods for tracking, Doesn't that also change the pitch of the blades in relation to each other if the rods don't end up exactly the same length when the tracking is spot on? If thats so how do you get the tracking right and still keep the blade pitch equal because I'm wondering if that could be causing the shimmying?

Could the head itself (that the feathering shaft goes through) have gotten bent?


I took a quick vid of what it's doing, you can see it mainly in the how the skids shake.

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Old May 27, 2011, 10:05 PM
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That looked more like gain shimmy from the 3 axis gyro rather than anything mechanical from the heli.

I can't really tell, but it looks like the shimmy is only intermitant rather than all of the time?
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Old May 28, 2011, 06:25 AM
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Originally Posted by Xrayted View Post
That looked more like gain shimmy from the 3 axis gyro rather than anything mechanical from the heli.

I can't really tell, but it looks like the shimmy is only intermitant rather than all of the time?
I did try turning the ele and ail gyro gain down at one point while trouble shooting because I thought the same thing but it didn't seem to change anything at all, aside from making it a little harder to keep it steady. The other thing is I had not touched any of the pots on the gyro/rx before or after the crash and like I said, it worked perfect before the crash.

I'll play around with the gains a little more next time I get a chance. It does have a pot that walkera describes as "balance control delay" that I didn't mess with...could that being to high cause this?
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Old May 28, 2011, 08:26 AM
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Originally Posted by candy76man View Post
I did try turning the ele and ail gyro gain down at one point while trouble shooting because I thought the same thing but it didn't seem to change anything at all, aside from making it a little harder to keep it steady. The other thing is I had not touched any of the pots on the gyro/rx before or after the crash and like I said, it worked perfect before the crash.

I'll play around with the gains a little more next time I get a chance. It does have a pot that walkera describes as "balance control delay" that I didn't mess with...could that being to high cause this?
It's hard to tell from vid,but does it shimmy all of the time it's in the air or does the shimmy come in waves? If it's all the time I would suspect something is still bent or out of balance. Bent parts or bad tracking usually cause vibrations all of time but 3 axis gyro gain shimmy can come in and out depending on what you are doing with the heli.


Look for bent parts or vibes by spinning the heli up with only the main shaft first and no head, then slowly add parts until you have the blades on. This allows you to observe the heli spun up and you will know at what point you added something that suddenly caused the heli to change or vibrations to occur.

If I remember correctly, the balance control delay determines how fast the elevator and aileron servos react and correct. This could possibly cause the cyclic servos to shimmy if the gain is too high just like the tail will on any other heli. You still need to determine that the mechanical setup on your heli after crash is perfect and smooth with no vibrations before making any gyro changes. It's possible that vibes are causing your gyro to act up and this would explain why it was fine with the current settings before the crash.
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Old May 28, 2011, 04:20 PM
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At least she's not beginning to crack up...

http://www.youtube.com/watch?v=rbtOa...eature=related

Sorry - just couldn't resist. Hope you get it solved.
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Old May 28, 2011, 07:47 PM
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xrated..... the shimmying does seem to smooth out periodicly when I'm hovering so hopefully you're right, I should have time to give it a try tomorrow. I've done what you said and checked everything and it all looks straight and true when spinning.

lol @ karlik
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Old May 29, 2011, 07:46 AM
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xrated..... the shimmying does seem to smooth out periodicly when I'm hovering so hopefully you're right, I should have time to give it a try tomorrow. I've done what you said and checked everything and it all looks straight and true when spinning.

lol @ karlik
Another simple thing to check I overlooked is your main blade tightness. They should not be tightened down hard in the grips or the heli can wobble because they will need to lead and lag once spun up. They should be just tight enough that they don't flop all over the place but will move just a bit if you turn the heli sideways.
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Old May 29, 2011, 01:47 PM
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it's a no go....reducing the gyros Bal-D setting didn't reduce the wobble at all and I tried loosening the blades a little so they could swing more freely and that didn't change anything either. When I'm spinning it up it will start shaking pretty bad once or twice at lower rpms and then smooth out as the head speed increases,...it only does this with the blades installed, when they are off it's smooth and yet the blades are balanced and equal weight.

Also, on the grip tie rods I have to have one about one 360 degree turn longer than the other(1 to 2 mm maybe) to get the blades to track right...is that an indication of a problem elsewhere?
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Old May 29, 2011, 05:20 PM
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it's a no go....reducing the gyros Bal-D setting didn't reduce the wobble at all and I tried loosening the blades a little so they could swing more freely and that didn't change anything either. When I'm spinning it up it will start shaking pretty bad once or twice at lower rpms and then smooth out as the head speed increases,...it only does this with the blades installed, when they are off it's smooth and yet the blades are balanced and equal weight.

Also, on the grip tie rods I have to have one about one 360 degree turn longer than the other(1 to 2 mm maybe) to get the blades to track right...is that an indication of a problem elsewhere?
Hmmmmm. Something smells since you only get the vibes with the blades on but it's hard to know if this is just the normal vibration until the blades find their position. They should be smooth at flight RPM. Do you have another pair to try for kicks? Try and do a full balance on those blades both for center of gravity and static balance. It's not always good enough for them to be the same weight. I've had cheap
FG blades that were off with the COG that flew terrible.

Start by finding the COG of each blade. Balance them on the edge of a ruler or something thin and mark the COG of each blade. The marks should be in the same place when the blade edges are laid next to each other. If they are then static balance them together again and only apply weight to the COG mark of the lighter blade.

If they don't both have the same COG, first correct one blade with tape until the COG is the same for
both. Then static balance them again together and see if they are in balance. If not, add tape to the COG of the lighter blade until balanced. This will ensure that the blades both have the same COG and
are static balanced with each other.

Sorry if you have already done this but just making sure it's not something simple like a bad blade balance.
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Old May 29, 2011, 07:41 PM
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Hmmmmm. Something smells since you only get the vibes with the blades on but it's hard to know if this is just the normal vibration until the blades find their position. They should be smooth at flight RPM. Do you have another pair to try for kicks? Try and do a full balance on those blades both for center of gravity and static balance. It's not always good enough for them to be the same weight. I've had cheap
FG blades that were off with the COG that flew terrible.

Start by finding the COG of each blade. Balance them on the edge of a ruler or something thin and mark the COG of each blade. The marks should be in the same place when the blade edges are laid next to each other. If they are then static balance them together again and only apply weight to the COG mark of the lighter blade.

If they don't both have the same COG, first correct one blade with tape until the COG is the same for
both. Then static balance them again together and see if they are in balance. If not, add tape to the COG of the lighter blade until balanced. This will ensure that the blades both have the same COG and
are static balanced with each other.

Sorry if you have already done this but just making sure it's not something simple like a bad blade balance.
Yeah I did check the blades and the cg on them is in the same spot and they are within less than 1 gram diff in weight between the two so I really don't think the blades are the problem.

I'm going to order a new grip assembly for it as thats the only part left that could possibly be tweaked. Maybe the one that holds the blade that hit the ground at high rpm got bent back just a hair? . If that doesn't solve the problem I don't know what I'll do
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Old May 29, 2011, 08:27 PM
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Yeah I did check the blades and the cg on them is in the same spot and they are within less than 1 gram diff in weight between the two so I really don't think the blades are the problem.

I'm going to order a new grip assembly for it as thats the only part left that could possibly be tweaked. Maybe the one that holds the blade that hit the ground at high rpm got bent back just a hair? . If that doesn't solve the problem I don't know what I'll do
That sucks. I would be really surprised that you were able to get the tracking so easy if the grip was bent, but you have already changed out all the other usual suspects that could be bent. Not much else up there it could be

Good luck with it
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Old May 29, 2011, 11:05 PM
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That sucks. I would be really surprised that you were able to get the tracking so easy if the grip was bent, but you have already changed out all the other usual suspects that could be bent. Not much else up there it could be

Good luck with it
I don't know, maybe a servo got damaged but I can't see any problem with them when it's sitting on the ground...none of them have broken gears anyway
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Old Oct 10, 2011, 08:36 PM
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pinion too tight to the main gear?
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Old Oct 11, 2011, 12:14 PM
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It may be the servos. Try this , disconect the motors and try moving the servos on the swash with the radio. If they move ok then put your finger on one at a time while moving the swash with the radio .
The only other thing could be the rx. It could be intermittent sending a signal to the servos.
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Old Jan 22, 2012, 04:16 PM
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Hello.

My 450d01 does same thing.

It shims when throttle up from low to high rpm.

I already pot down the ail gain. Not much effect....

here goes a video. I record it in flight:

http://www.youtube.com/watch?feature...&v=BisqkwjEXow


Any ideas?
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Last edited by pilotonovato; Jan 22, 2012 at 04:21 PM.
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