Hi guys,

I have been having a problem with servos for a while now and don't know what the cause could be. Everyone else probably knows this, but I'm going to ask anyway:

I have had servos that 'bounce' after traversing to a position. It is most noticeable when you go from full deflection to center. The servos seem to 'bounce' back and forth around center.

Des anyone know what causes this? Is there some way of fixing this?

Thanks....

Does the servo do this when the load (pushrod tothe surface) is removed? If not, it is probably caused by the way the surface is hinged; either out of alignment, stiff or ?????.

Nope, this is completely unloaded on the ground. I would think air loads would 'damp' the bounce I am seeing on the ground.

What's the age, make and model of servo's that are doing this ?
Are you using a standard 4.8v nicad pack for supply ?

I had this problem It was caused by vibration from the motor causing the pushrod to the rudder to shake and it would wear a spot in the center of the servo feedback pot The servo could not find the right place to center so it would bounce from one side to another.Try moving your trim on the transmitter as a test which would cause the servo to center in a new place.I would say you have a vibration problem on you surfaces.Flutter on the control surfaces or long pushrods that should be supported.I used up three servoes before I figured out what it was. I would get about five flights and then the servo would start bouncing, It was the Nyrod shaking because I fastened it at the servo and at the tail but not in the middle.I was blaming the cheap servos and was complaing to a friend when he found out the servo I was using he stated they were the best servos he found for use in his high speed racing plane.Then I checked over my installation and found the problem.If you are happy with pushrods ETC then check to see that the servo is not touching the beams but is hanging in the mount by the rubber grommets.It really sounds like a vibration problem to me

I have an Futaba 9601 that does the same thing when I first turn on the radio without the engine running. The hinges, push rod, mounting, etc. are all fine. It's definitely the servo. Moving the stick back and forth a few times clears the condition until the next time I shut down the radio, wait a few minutes, and turn it back on. I believe it's the feedback pot, but haven't tried to clean or replace it yet. I'm running a 700 MaH 4.8V Ni Cd. The problem became apparent after the servo had been in storage for about 6 years.

John

If you plug the servo direct to the rx and the problem goes it is the signal wire is not transmitting a clean signal this is the white on Fut and orange on JR
hope this helps
M

I've had that happen mostly on servos that have extensions on them. For some reason, whether it be connector type, or wire used, replacing the bouncing servo extension usually cures the problem. Try twisting the wires if it does not have an extension on it. Let me know what you find_bob

Hmmm, very good ideas. In fact, the servo is attached to an aileron and it is attached to a Y-harness. I will remove the Y-harness this weekend and see what happens.

John

Keep me posted!

I have a 605 on one half of the elevator of my H9 Edge that has developed a very noticable bounce when centering. I was wonderong if maybe the pot was going in the servo. I guess I need to up date all my servos to digitals.

My aileron servos on my Fazer Fun Fly do that. Mine is caused by the gears being very worn due to the 300+ flights on that plane. I have MG high torque servos on the tail and they don't do that yet. When I move the control surface and let it pop back to the middle it will bounce back and forth with the slop in the gear trying to find center.

If "bouncing" is more like fast chattering near the neutral point, then I would suspect a worn or dirty feedback pot.

But if "bouncing" is more like a door swinging back and forth before finally stopping, then I would suspect your Y-harness....especially if it's the cheaper Hobbico Y-harness.

Corrosion builds up on the contacts, which severely reduces the voltage to the servo when it's under a load. Plugging the servo in and out of the extension several times, or plugging the extension in and out of the receiver several times may temporarily cure the problem.....but it will come back.

If you used the cheaper Hobbico extension, you can cure the problem permenently by replacing it with a Futaba, JR, Hitec, or even the Hobbico Pro series Y-harness.

You're not alone with this problem. Check out this info in the rec.models.rc.air newsgroup:
http://*****.com/hobbico_extensions

I have the same problem with the servos in the wing of my US60. They are Futaba 3001s and when the crow switch is on and then switched back to normal the servos return back to center then bounce once and go back to center. I do have extensions on the ailerons but not the flaps. There is less than 25 flights on these servos.
fossil

On my 9601 servo, the gears are absolutely tight. The bounce is like a spring loaded door swinging back and forth. The Y-harness is a JR model. I can't remember if it has the built in amp or not. I really don't even remember if it was new or one I have had on hand for a while when I installed it. I've used these Y's on these very same servos in a previous model without any problems so I know they are compatible. Hopefully, I'll have time to bypass it tonight. But, if it is the connector, then cleaning it and using a little dielectric grease should resolve the problem. We'll see

John

If it's a JR, chances are good it's amplified. Not saying that's the cause, just that it's probably amplified. Are there extensions running back to it? I've found extensions to be the culprit more often than not_bob

Yep, there is an extention between the Y and the RX. I'll eliminate both as soon as I can.

John

As a side note, you should use the Y right at the receiver, and use two extensions from there, rather than using an extension from the receiver, then a Y at the servo end. Using the Y at the receiver will reduce the resistance of the wiring to the servos, allow for better current handling, which will both help keep the maximum voltage at the servos. Its also best to use heavy duty wiring for the extensions and the Y itself for the same reason.

I've used the following configuration for the past 17 years without an issue before now. RX>extention>Y>servos. I understand in a perfect world, you might want to do something different, but this is how I setup all of my pattern planes in the past as well as all of my sport planes then and now. The Y at the receiver would require an additional extention in the wing to reach the servos which not only adds cost, but weight and two connections which must be made when the wing is installed or removed instead of just one the way I've been setting them up. If it's wiring that's the problem, I'll replace or clean them, but I'm not changing my ways just because of this one glitch I'm sure it will be an easy fix, I just need to find the spare 10 minutes to fix it.

John

I have had that happen to my 3004 Futaba servos and in all instances it was cleared up by replacing the extension wires. The extensions all checked out good, not sure what about them was causeing the bounce but it was definatly cured by replacing them

I had the same thing except it was with the servos pluged in ch1 and ch6 for dual ail. ch 6 would flop around center then go away, some times you could flex the surface up and down with the radio on then it would lock on Sent set in for check up they found ch 6 in the TX was weak did some repair and it was fixed. I was swapping servos thinking I had a batch of bad ones

Bouncy, bouncy!

Had the same thing happen with Y harness and extenison. All stretched out I'd guess 3 1/2' from servo to receiver including Y.
I figured interference from long leads, too much voltage drop, or .... Yep, quality of the leads and connections.