Pixhawk on tricopter - yaw problem


I have tricopter with pixhawk fc. It is my first tricopter. I've already tuned 6 or 7 quads controlled by APM and everything was good. Roll and pitch pids are perfect, but i can't deal with yaw on my tricopter. It wobbles.

At first there was backlash in yaw servo, i've replaced servo, but it made no noticeable difference. I've changed configuration, tried different methods of yaw pid tuning, removed vibration, reinforced booms but can't get away from wobble.

I'm getting lower wobble if i'm lowering yaw stab p. It makes copter sluggish, but wobble is still there.
I do not know what to do next. Today i installed naze32 into this frame, just to see how it will behave. And it is rock solid in yaw although pids are poorly tuned.

Does APM can handle yaw without wobble? I'm using 2-axis gimbal and wobbling on yaw drives me crazy.
Does RC_SPEED affects yaw servo? I have digital TGY-390DMH servo. It must handle 490hz...

What else can i check? Does anybody has tricopter controlled by APM without yaw wobble?

It is not hardware problem, because naze32 fully fixed it.

I've tried to install v3.3rc10, to give a try for yaw autotune. It completed sucessfully, but it made yaw so sluggish and wobble...

Any advice would be helpfull.


I've found interesting thing with my logic analyzer (screen attached). Servo is working on 50hz, and RC_SPEED parameter changes only motor output frequency. And I can't find how to change servo output frequency. I do not want to dig APM code... May be anyone knows how to change servo frequency?


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