High @ all!

I like to build a 3 achsis gimbal with the landing gear to be turned with the yaw achsis.
I have a problem with installing the yaw achsis properly.

My Gimbal is that one here,
http://www.hobbyking.com/hobbyking/store/__51513__ACK_Pro_Mid_Sized_Ball_Bearing_Brushless_Gimbal_With_Turnigy_4008_Motors_NEX5_And_GF3_Sized_.html
in combination with a yaw achsis landing gear with GBM 5208 150T motor.
I am using the 32 bit board V3, firmware is 2.43b9 with 2 IMU, the frame IMU below yaw.
After balancing all sensors were calibrated the complete way.
Roll and Pitch are fine.
But the yaw achsis keeps turning. That means, the whole copter on top of the gimbal starts slowly turning after powering the gimbal. I can force it in one or the other direction, but once it starts turning it gets quicker and I have to hold it.
I can imagine that there is no input to the board from the IMU's about the movement, because they are fix at the gimbal, which does not move. If there is no signal of movement, there is no reaction to hold it and slowly it starts turning and gets faster.
I guess, I have to trick somehow the controller to keep the yaw motor from turning.
I tried already to mount the Frame IMU above yaw, but it was the same behaviour.
Once the copter is in the air, the movement stops, because the Gimbal moves instead of the copter and the IMU's give the signal to the board.
But how to stop the yaw achsis as long as the copter is aground?
Thank you for any recommendations.

Fishermen