whats wrong with the tail servo

[kwegrzyn]

Hello
Testing , testing , testing - what can be the reason when during high engine rpm tail servo starts to oscillate .
Everything is fine when spooling up to about 50% of engine rpm , when more than 50% tail servo starts to oscillate causing wagging of heli , I have tried almost all setup possibilities ( p-gain high/low , etc.)
I removed main blades and observed it on servo . Simply starts to move (oscillate ) above some point of engine rpm.
Bavarian axon , futaba radio , trex 450 dfc plus.
Any clues ?
Regards
Kris

[Dogdipstick]

What is the (tail) gain setting and how does it affect the behavior durring testing f?

[kwegrzyn]

Tail gain was tested with almost all range together with p-gain and d-gain combinations
Now is tail gain is 60 , p-gain 9 , d-gain 0 , this are the settings when oscillation is lowest possible but it is .

[AndrewJHawes]

Just to be absolutely sure, 'wag' or 'bob'?

[kwegrzyn]

It’s a wag

[Smoggie]

Vibrations could do it. Has the heli been crashed, could anything be bent?

It would be good to try with both main and tail blades removed. that would check if the servo is over compensating (gain too high) or if it's some other cause that makes the servo oscillate.

[Dawiev]

IMHO a slow wag is most of the time a mechanical issue, regardless of the FBL system. Especially, if gain changes doesn't affect the behaviour.

It could be a thrust bearing the wrong way round (feels smooth on the bench, but "binds" at high headspeed), or any of the other common culprits. The tail mechanics should be butter-smooth, else you will be chasing........ your tail !

[DUCDOC]

Always check your links for proper sizing and slop free movement. If it's not butter smooth a slow wag ( mechanical ) can develop and no gain adjustment will get rid of it.