Correct way to fix the robot in space

Hi, currently I’m facing an issue that I couldn’t fix.
I want to fix the robot to space (not to the ground) like AllegoryHand, which does not fall by gravity but its entire body can translate anywhere after simulation started.

First, I converted urdf file to usd file without checking “fix base link”.
In addition, I added empty Xform and fixed joint which connects the Xform and the root link of the robot.
However, when I changed the translation of top-level prim of the robot after simulation started, the root link is fixed at (0, 0, 0).

On the other hand, when I disabled gravity at all links, the robot does not fall and can translate anywhere. But the robot floated away slowly because the robot is not fixed anywhere.

What is correct way to fix the robot in space like AllegoryHand?

I solved this issue by converting urdf file and added fixed joint under the top-level prim of the robot which connects the root link and empty in Issac sim ver 2023.1.0-hotfix.1.
In ver 2023.1.0-hotfix.1, the articulation root exists at the top-level prim of the robot, and exists at the root link of the robot in Issac sim ver 2023.1.1.

What is the relationship between the change in location of the articulation root and this problem?

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