[Question] How to get contact forces/torques in the local/body frame?

[kbkartik]

Currently, net_forces_w and force_matrix_w are in the world frame. If I want to assign a contact sensor on Shadow hand's fingertips, how do I retrieve net forces and force matrix in the local/body frame?

On a similar note, in which frame does get_measured_joint_forces() give the force/torque values?

[RandomOakForest]

Thanks for posting this. You may benefit from using a frame transformer.

[Mayankm96]

You always receive the contact forces in the world frame. If you wish to transform them to some other frame, you can use the math utilities inside isaaclab.utils.math to convert them to the desired frame.

@RandomOakForest The frame transformer only provides the pose transformations between a target and source frame. You can use it to get relative transformations. But you can also just use the asset data (body_state_w) to get the poses in the world frame.

Also contact sensor has a track_pose attribute which returns the pose of the rigid body the contact sensor is attached to.

[kbkartik]

Thanks for the prompt reply!

I am bit confused. Given a contact sensor $C$ with reference frame $F_c$ assigned to Shadow Hand's fingertip reference frame $F_{tip}$, currently, the API gives me $f_{world, Fc}$. However, I want the force $f_{Ftip,Fc}$. How do I get this?

Similarly, for 6AF, in which frame does get_measured_joint_forces() give me forces/torques?

If I understand correctly, given two frames, $F_{world,1}$ and $F_{world,2}$, frame transformer gives me $T_{F_1,F_2}$.

I am new to this and am probably overseeing something. Let me know your thoughts.

[RandomOakForest]

Thank you for following up. I'll move this to our Discussions section.