[ODE] what is wrong with amotor joint?

[Krystian Ligenza]

maybe with this two movies I could show my problem clearier:
http://www.pjwstk.edu.pl/~s2562/ragdoll_noAdd.avi
http://www.pjwstk.edu.pl/~s2562/ragdoll_addTorque.avi

As I mentioned earlier, I wanted to add PS controller to my radgoll, using
well know equation:
torque = Kp*(des - cur) - Kd*vel;

For this tests, the Kd is set to 0. First movie shows a ragdoll with PD
controller applied only to hinge and universal joints (ball joint with
AMotor joint are set for spine,chest and head). Everything looks "ok". But
when I add torque to AMotor joint, joints start to shake (second movie) -
were is the problem?

Thanks
Krystian