[Question] Effort control mode (instead of position control)

[ADebor]

Hi there,

I'm currently modifying the ShadowHand example you provide in order to control the hand using efforts rather than position control. To do that, I use the set_joint_efforts method on the hand view (instance of ShadowHandView(ArticulationView)) instead of setting position targets and using set_joint_position_targets as done in the provided example.

This seems to work (the hand does move when using a random policy), but since the get_applied_joint_efforts method isn't working (apparently a known bug that will be fixed soon, or is fixed and the problem is on my side) and returns nothing but zero efforts in the joints, I cannot really investigate and check that everything is working properly.

What I am curious about is the set_drive call in the ShadowHand class. This call sets the drive type to either linear or angular through pxr.UsdPhysics.DriveAPI, as well as the target position or velocity to 0.0. Is this some kind of initialization step required with usd, or is this related to some behind-the-scene mechanism underlying the control of the hand, not depending on the type of control I choose using the Python API (e.g. by using switch_control_mode), and preventing me from doing effort control on the hand?

I apologize if this is a silly question, and don't hesitate to tell me if it shoud be asked on the dev forum rather than here. Thanks!

[kellyguo11]

Hi there, the UsdPhysics.DriveAPI schema shouldn't be required for effort control. You can set both the damping and stiffness values on the drives to be 0 for effort control. They are used mainly for position/velocity target controls. You can find more details about it in the USD documentation here.

[ADebor]

Thanks a lot @kellyguo11!