How can i control Spherical Joint in Simscape Multibody?

I am trying to control the arm in the picture with the simulink model as shown below. Even when I don't give any input, spherical joint moves on its own uncontrollaby.

Answer 1

[Steve Miller]

Your model is moving due to gravity. The inputs you have specified are torques, not motions. If you apply 0 torque, the arm will move like a spherical pendulum.

Here are two options:

1. Switch to a Gimbal Joint. This also permits 3 degrees of freedom, and you can motion actuate each one. Just make sure you don't go into gimbal lock, where two of the degrees of freedom are aligned.
2. Use a PI or PID controller to control the torques to achieve the positions you want.

--Steve