Isaac Sim Version
4.5.0
Operating System
Ubuntu 22.04
Topic Description
Unable to import a URDF into Isaac Sim 4.5. Converting to MJCF and converting back to URDF doesn’t work either.
Detailed Description
I have combined two urdf.xacro files into one purely be referencing the two using <xacro: include…> statements. Individually, I am able to successfully import both files into Isaac Sim by going to File→ Import and configuring import settings. This goes as planned and I can see each of the assets in the stage.
Combining the two URDFs in another .urdf.xacro , and then running ros2 run xacro xacro combined.urdf.xacro > combined.urdf works as planned, and I am able to inspect my new URDF. It looks alright. However,
Error Messages
RuntimeError: Accessed Invalid null prim
Additional Information
What I’ve Tried
I tried converting the URDF to MJCF. However, that fails too. I am not sure why the URDF can’t be converted. It points to an error in the URDF itself, but after inspection, I am confused because the hierarchies/syntax/semantics seem alright.
Related Issues
Additional Context
I got to this error when trying to integrate MoveIt with the combined setup. MoveIt Startup Configurator requires a .urdf.xacro file to build packages. I had worked that bit out and have been able to plan and execute in RViz using MoveIt.
Since I wish to simulate this in Isaac Sim. The integration bit is doable since there is some literature on that part and I’ve done so before (i.e., integrating Isaac with MoveIt over ROS2). However, when I setup the manipulator and gripper in Isaac Sim by importing standalone URDFs and assembling them in Isaac, and flattened the hierarchy, the setup fails: there are no errors on both sides (Isaac Sim Console is empty and MoveIt executes the plans perfectly well).
Looking at the setup I felt that I should maintain naming and hierarchy. And so, directly thought it best to import the combined.urdf. And that’s where my problems began…