[Question] fail to convert usd to urdf

[ifmorning]

Question

I was trying to use the ControllerUtils.convert_usd_to_urdf() function in Isaac Lab to convert the usd file of my robot into an urdf file. But this fails due to kinematic loops in my robot. Does anyone know how to solve this problem?

[RandomOakForest]

Thank you for posting this. Should we assume simplifying the robot’s kinematic structure by breaking loops in the USD model before conversion is not an option?

[louislelay]

Hey @RandomOakForest, I'm not the original poster, but I'm running into the same issue. I'm working with a humanoid, and one of its models has a lot of closed kinematic loops. Manually breaking them in the USD before conversion would be very time-consuming. It would be great if there were a way to handle this more automatically!

[RandomOakForest]

Thanks for following up. I'll bring this up with the team.

[mpgussert]

hello!

Yes! Kinematic loops are not allowed within Isaac Sim as a consequence of the articulation system. Joints can be excluded from the articulation by specifying the "Exclude From Articulation" physics property on the joint itself.

Another option would be to export directly using Isaac Sim, but you will still have this kinematic constraint. you can find the details here! https://docs.isaacsim.omniverse.nvidia.com/4.5.0/robot_setup/ext_omni_exporter_urdf.html

hope this helps!
Gus

[ifmorning]

Thanks very much! @mpgussert I have set all those loop joints to be excluded from articulation, but it seems that there are still kinematic loop errors.

[RandomOakForest]

Thanks for following up. I'll move this to our Discussions for follow up.