Articulation not working when enabling a 4th articulated joint

I am trying to create a Delta robot in Isaac Sim. It seems to be working fine when I only enable the 3 articulation revolute joints controlling the translation movements, but when I add a forth articulation joint to control the rotation of the tool, it fails. What am I missing?

This is what shown in the terminal wondow:
2023-08-10 11:49:11 [512,702ms] [Error] [carb.physx.python] IndexError: index 3 is out of bounds for axis 0 with size 3

/home/fredribo/.local/share/ov/pkg/isaac_sim-2022.2.1/exts/omni.isaac.articulation_inspector/omni/isaac/articulation_inspector/ get_articulation_values
/home/fredribo/.local/share/ov/pkg/isaac_sim-2022.2.1/exts/omni.isaac.articulation_inspector/omni/isaac/articulation_inspector/ _on_physics_step

Codian_prt_m.usdz.usd (1.9 MB)

Hi @fredribo1 - The error message you’re seeing indicates that you’re trying to access an index that is out of bounds for the array. In this case, it seems like you’re trying to access the fourth joint (index 3, since Python uses 0-based indexing), but your array only has size 3 (indices 0, 1, 2).

This could be due to a few reasons:

  1. The fourth joint has not been properly added to the robot’s articulation. Make sure that the joint has been correctly defined in the robot’s URDF file and that it has been properly imported into Isaac Sim.

  2. The code that is trying to access the joint values is not aware that a fourth joint has been added. If you have code that is hard-coded to only consider three joints, you will need to update this to handle the fourth joint.

  3. There might be an issue with the way the joints are being indexed. Make sure that you’re using the correct indices when accessing the joint values.