Rigid body lock pose and lock rotation doesn't work when I set articulation root

Omniverse Isaac Sim
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1

I was trying to make walker2d on isaac sim. I made it simply by connecting rigid bodies by revolute joints. for walker2d to move on 2d plane, I wanted all rigid bodies to stay in the same plane parallel to xz plane. to do that, I have to lock movement along y axis, and locked rotation along x,z axis. It worked well, but to make rl environment I had to set articulation joint. when I set torso as articulation joint, my model didn’t work anymore. you will see how it didn’t work in the video below. rigid body was not locked anymore.
(241029_articulation_joint_unlocks_body.mp4 - Google Drive)
on this video, objects fall down on the ground plane with slope. left side is when torso is not articulation root. right side, when I set torso as articulation root, object makes y-axis movement, which I locked.

Isaac Sim Version:4.2.0
Operating System: Ubuntu 22.04
GPU Information:

  • Model: NVIDIA RTX 2070 super
  • Driver Version: 535.183.01 CUDA Version: 12.2

Steps to Reproduce:

  1. made a robot with rigid bodies connected with revolute joint rotating around y axis
  2. set all rigid bodies to have lock pose on y axis, lock rotation on x, z, axis
  3. set articulation root
  4. make ground plane with slope
2

Locking dofs does not work for articulations. You can use a properly configured D6 joint to achieve this, however. Just lock the degrees of freedom of the articulation root link to a plane.