URDF converter seems broken when set merge_joints?

[catachiii]

Discussed in https://github.com/isaac-sim/IsaacLab/discussions/545

^{Originally posted by **catachiii** June 20, 2024} ### Description Dear IsaacLab team. Thanks for providing us with up-to-date USD files for all kinds of humanoids. I have couple of questions about the necessary procedures using the urdf_converter to import the urdf to USD myself. Taking the URDFs of Unitree H1 for example (https://github.com/unitreerobotics/unitree_ros/tree/master/robots/h1_description/urdf), I have been trying to convert the given URDF to USD files with the How-to guide (https://isaac-sim.github.io/IsaacLab/source/how-to/import_new_asset.html). I successfully converted the URDF with `--merge-joints` and `--make-instanceable`. However, when I'm loading the humanoid USD file similarly to the demos (https://github.com/isaac-sim/IsaacLab/blob/main/source/standalone/demos/bipeds.py). I encountered the issue that some of the visuals (like the logos, etc.) are not updated with physics, as shown below.  I'm not sure what I missed when converting. So far, all quadruped URDFs from Unitree work fine and similarly to what is provided from the Nucleus server. Thanks for your help! I also noticed there was a PR weeks ago importing Unitree G1 successfully. @abizovnuralem @Dhoeller19 would you mind sharing your experience with me?

Jin

Update:

I tried without --merge_joints, and now the visuals look all good. But the simulation can easily explode with the following error

2024-06-20 11:01:56 [57,157ms] [Error] [omni.physx.plugin] PhysX error: Illegal BroadPhaseUpdateData , FILE /builds/omniverse/physics/physx/source/lowlevelaabb/src/BpBroadPhaseABP.cpp, LINE 4023

[catachiii]

Follow up:

I also tried to import a URDF containing Spot with the arm (https://github.com/heuristicus/spot_ros/tree/master) following the actuators given by the examples, but the simulation still explodes with and without --merge_joints.

I really hope we can have more robots that are customizable for isaaclab.