Bucking Bronco Motion

[Allan114]

My 180 was flying perfectly the other day but when I took it out today I spooled up in Normal mode and everything is fine then when I hit stunt mode and the head speed increased it started pitching up the tail acting like a bucking bronco. Coming back down to Normal speed (25% throttle) and the bucking motion stopped. I flew a couple of batteries but every time I tried stunt mode the bucking would start to such an extent that it made it difficult to fly. It was almost like it was a jittery elevator servo but there is no jitter in Normal mode and no sign of servo issues when testing on the ground. There have been no crashes, this just started out of the blue.

So far I've checked the feathering shaft, TT and main spindle but nothing amiss. Could this be some electronic issue?

[jamichx]

Are you saying that tail is going up and down ? If that what you mean then maybe elevator servo is playing when under the load. Just guessing here.

[Len Todd]

Feathering shaft bent or snubbers worn out? But, the servo is a good place to start too.

[Allan114]

Yes it is the tail bouncing up and down. I think the servo is ok because in normal mode there is no bucking and no sign of it on ground runs. The feathering shaft is straight but what do you mean by snubbers?

[spoonerrw]

I think he means the feathering shaft dampeners? I had this happen one time, and the dampeners were worn out. replaced them and the issue went away.

[Allan114]

Thanks I've replaced the feathering shaft dampers in the rotor head from an old spare one. I've also put O ring dampers on the swash ball joints to see if that helps.

[Allan114]

Originally Posted by Allan114

Thanks I've replaced the feathering shaft dampers in the rotor head from an old spare one. I've also put O ring dampers on the swash ball joints to see if that helps.

The above helped a lot but in the end I swapped out the elevator servo and now the bucking motion has gone. I don't know what is wrong with the servo as on the bench it is perfect, even when I load it a bit against my finger. It is one of my metal gear conversions so am going to swap out the motor unit bit with another gear damaged servo I have so I can keep the metal gears i the heli.