PD gains use different units in Isaac Lab and USD

[Wang-Haitong]

Hi, I recently found that the damping and stiffness coefficient in USD and Isaac Lab use different units. In Isaac Sim GUI, we can see that damping and stiffness uses degree; while in Isaac Lab, these two coefficients use radian. And when we set damping and stiffness to None in actuator cfg, Issac Lab would use the default values in USD prim, which would be multiplied by 180/PI.

I think it would be better if this difference can be mentioned in the docstring of actuator cfg and documentation as it can cause problems that are hard to debug.

[Dhoeller19]

Hi @Wang-Haitong,
Indeed, it is a great idea to mention this in the docs.