[Question] Default stiffness and damping gains for robot arm manipulators

[elvisbreit]

Question

I want to tune the PD gains of the robot arm manipulator UR5e with an external load mounted on the flange. I have checked the values provided for the robot in the Isaac Sim Asset Browser and I am wondering on what basis the default damping and stiffness parameters were chosen. The default parameters specifically from the UR5e are shown in the following screenshot if opening the Gain Tuner window:

In general, were these values for all robot arm manipulators derived using the Gain Tuner, and if so, what steps were followed? Or were they obtained through modal analysis, and then used to calculate the stiffness and damping gains?

[PeterL-NV]

Hi, those defaults come from a rigid-body joint-drive (spring-damper) model parameterized by a target natural frequency and damping ratio — not from structural/modal analysis in the FEM eigenmode sense.
The "basis" for a robot's default gains is: pick a target natural frequency and damping ratio, then compute Kp/Kd from the equivalent inertia.
Please refer to the Gain Tuner Extension for more details on this topic.

[PeterL-NV]

Hi, we hope the explanation above was helpful — the default PD gains are derived from a spring-damper model parameterized by a target natural frequency and damping ratio, not FEM modal analysis. Since we haven't heard back in a while, we'll go ahead and close this discussion. If you have further questions about tuning gains with an external load, please open a new discussion and reference this one.