Simulation 3d

[rf96]

1) Before the start: the disk don't turn around itself. After, the disk turns around itself because the red arm want to change its orientation. The angular velocity of the disk is cos(a)*w with 'a' the angle of the axis of the orange disk from the vertical, and 'w' is the angular velocity of the red arm. This formula is confirmed by the simulation (a=62°). I don't know how the red arm receives a torque from the disk maybe you know ?

2/ With a spring: look at the video, you can watch the fixed black circle moves up (altitude from the ground). The spring will increase its potential energy. And what is the angular velocity of the orange disk ? It is lower than the support but the disk turns in the direction of the angular velocity of the support, so the disk will increase its angular velocity not decrease it.

Look at the angular velocity from the simulator:

http://s5.postimg.org/mg0m34mhj/ang_Vel.png

The simulator gives a negative sign because the angular velocity is relatively of the red arm not the ground.

So maybe the support receives a negative torque, but I don't find it, and you ?

[rf96]

I understood how the support receives the torque with the spring

But how the arm receives the torque at start when the support accelerates ? Because like the disk accelerate around itself in the lab reference it has more energy so the arm must receive a torque.