How to measure the external torque exerted on a passive rotating joint in a closed chain?

[HuNingHe]

I try to create a motor device on this passive hinge joint, but this results in the passive joint generating an active torque to counteract the external force.
I want to know how the torque on the passive joint changes with the active joint movement
Is there any possible way？Thanks

[omichel]

Yes, depending on how the motor was configured, it will try to keep a position and hence will apply a torque to maintain this position. If you want to disable the torque resulting from this, you can set it to 0 with wb_motor_set_available_torque, so that it will disable the position servo control.