Carbon Z Cub elevator servo noise.

[Bluebird]

Hi there gang. After about 20 flights on my Carbon Z Cub the elevator servo started making a whining screeching noise but still seemed to work. I automatically replaced it with the same 26 gram servo from E Flyte. Now after a dozen or so flights the new one is doing the same thing. I took the original one apart yesterday and couldn't see any visible damage inside though it was very stiff when trying to move it mechanically.
Has anyone else had this experience and if so what servo have you used to replace the stock one? I have a feeling this one is being overloaded by the large elevators on this airplane.
Regards, Bluebird

[xviper]

Sometimes, the servos on my old CZ Cub (and same with the CZ T-28) would buzz or hum depending on if there was any resistance on it from the control surface when at rest. Eflite servos tend to do that normally. Does the noise go away when you operate the servo and if you wiggle the stick, does the servo find a "happier" place where it stops the noise? If you think there might some stiffness in the elevator, remove and the control rod and manually move the elevator. Does is seem like it's tight or hard to move? That might answer that question. In the air, the servo should handle whatever is thrown at it. Moving those bigger servos mechanically will always be stiff and is probably not a good idea to do too often or too fast.

[Bluebird]

Thanks xviper2 for your reply. Unfortunately there seems to be no "happy place" for the servo except when not moving, at which point it makes no sound. It makes the noise through out the whole range of movement no matter what I do. When I changed the servo the first time I checked the elevator movement but there was minimal resistance. This is a mystery as the other servos operate normally and its only the elevator that has these issues. I may try reducing the throw on it although presently set at only 90%.
Cheers! Bluebird

[WintrSol]

Since it is apart, you can try silicone or white lithium grease on the gears; be careful not to contaminate the electronics. Re-assemble and see how it sounds.

[Bluebird]

Hi WintrSol Good idea! However I was surprised and impressed by the amount of white grease in the thing already. They are metal gears and they appear well lubricated.

I will reduce the throw from 90% to 70% tomorrow and try that to see if it helps incase I'm maybe at one end of the stroke. However the elevator movement seems equal in both directions so I'm really just throwing stuff at the wall to see if anything sticks. Next step will be to disconnect the elevators and try the servo on its own with 0 load.

If I find anything out I'll post it for those interested. Thanks for your input!

[WintrSol]

Well, if the gears are that well lubricated, the only other moving part is the motor. Careful application of light oil, with a needle-like applicator to the motor bearings could help, unless the noise is coming from the commutator; that would be very hard to deal with.

[Bluebird]

Yes that is a good idea WintrSol. Also the top bearing that the servo shaft runs in was without grease. The grease is on the gears only, so there are some other items I could lubricate, The motor is the most important as it turns much faster than the output shaft. The output shaft not really requiring too much lubrication I would think.

I will see what I can do about that!

Thanks! Bluebird