Result of root_physx_view.get_link_incoming_joint_force() is Incorrect in some cases

Omniverse Isaac Sim
1

Isaac Sim Version

4.5.0

Operating System

Ubuntu 22.04

GPU Information

  • 4090D

Topic Description

Detailed Description

Hi, currently I’m facing an issue that I couldn’t fix. I tried to obtain the net wrench experienced at the float base, like what I have done in isaacgym by calling the refresh_force_sensor_tensor() to obtain root wrench in the world. However, the incoming wrench at the root is [0., 0., 0., 0., 0., 0.] at the root of the kinematic tree in isaaclab. To cope with that case, I addded a parent body to the original root body and connnected then with a fixed joint. Then I defined the added body as the new root and read the incoming wrench at the original root. For a humanoid walking case, the force component in the z-axis is always minus, which seems to be unreal.

3

Hi @792365484, the physics APIs currently do not support getting forces and moments of the floating base, but one thing you could try is to get all the forces on the root rigid body in the same reference frame and sum them up. That should give you exactly the forces/moments on that body. For instance:

  1. If you call get_measured_joint_forces() on the Articulation, you can get the forces/moment vector corresponding to all the joints connected to the pelvis (I believe these will be in the local pelvis frame).
  2. Then you just need to get the gravity force in the pelvis frame as well.
  3. Add them all up.

I hope that helps.

In the meantime I can make a request for the feature to be included. What is the use or purpose of getting the forces/moments on the floating base?

4

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