Hello I am trying to follow the tutorial to generate the necessary files to run Lula Kinematics Solver on my custom robot epson.usdc see attached. Robot Description Editor Issue I am currently stuck at generating the robot description file using Robot Description Editor (https://docs.isaacsim.omniverse.nvidia.com/4.5.0/manipulators/manipulators_robot_description_editor.html) I launched the .usdc file and tried accessing the links. I can see my robot under Articulation but I don’t see anything under Link (See snippet attached) . I have successfully rigged my robot and I can easily move every joint using Physics Inspector. I don’t know what I am missing here. URDF Export I am also trying to export my .usdc to .urdf so I can feed it to the Lula Kinematics Solver. However upon export I get the following error. But I don’t understand what it means (see attached urdf_export_error.txt). You can also find my epson.usdc file attached as well. Any help would be appreciated thanks!
You might want to try the Asset Validation feature in Isaac Sim to help troubleshoot this issue. If your robot’s links aren’t appearing in the Lula Robot Description Editor, it could be due to missing or misconfigured elements in your USD asset—such as absent robotLinks relationships, missing APIs, or issues with joint/link definitions.
Thanks VickNV for helping out with this. I just realized an error was being thrown when I selected my robot in Lula Robot Description Editor. Find the error below:
2025-09-24T19:25:45Z [2,321,793ms] [Error] [omni.physx.tensors.plugin] Simulation view object is invalidated and cannot be used again to call getSharedMetatype
2025-09-24T19:25:45Z [2,321,793ms] [Error] [omni.ui.python] AttributeError: 'NoneType' object has no attribute 'link_names'
At:
/opt/air/isaac-sim/exts/isaacsim.core.prims/isaacsim/core/prims/impl/articulation.py(5166): _on_physics_ready
/opt/air/isaac-sim/exts/isaacsim.core.prims/isaacsim/core/prims/impl/articulation.py(181): __init__
/opt/air/isaac-sim/exts/isaacsim.core.prims/isaacsim/core/prims/impl/single_articulation.py(110): __init__
/opt/air/isaac-sim/exts/isaacsim.robot_setup.xrdf_editor/isaacsim/robot_setup/xrdf_editor/extension.py(250): _on_selection
/opt/air/isaac-sim/exts/isaacsim.robot_setup.xrdf_editor/isaacsim/robot_setup/xrdf_editor/extension.py(281): _on_combobox_selection
/opt/air/isaac-sim/exts/isaacsim.gui.components/isaacsim/gui/components/widgets.py(55): <lambda>
Also, I tried running the Asset Validator tool I can see I have a few errors but I am unsure as to how to fix them (I don’t even know how significant the error raised are). Any advice you could give me:
JointHasCorrectTransformAndState: Joint Epson/Joints/J2 Rotation not well defined, From body 0: […] From body 1: […]. This applies to all joints. I don’t know why this is happening I’ve created the joints using the UI.
RigidBodyHasMassAPI: RigidBody /Epson/gripperV57_m_rotated/GripperV57_m_rotated_001’s principal axes is not normalized, but: 0.0. This applies to all joints
Thanks for sharing your issue and the asset validation results.
The core issue is that your Epson robot USD file lacks the essential robot metadata that Isaac Sim’s Lula system requires. The missing robotLinks and robotJoints relationships cause the physics articulation view to fail initialization, resulting in the ‘NoneType’ object has no attribute ‘link_names’ error. Additionally, the joint transform inconsistencies prevent proper URDF export.
To help narrow down the cause, could you provide a bit more detail about the origin of your epson.usdc robot file?
Was it exported from an external tool (e.g., CAD software, another simulator), authored manually, or converted from another format?
Has this file worked previously in Isaac Sim or another environment/version? If so, which version and workflow did you use?
Knowing whether the asset functioned as expected before can help identify if the issue is with asset contents, changes in the USD structure, or compatibility with current Isaac Sim releases.
If you made any adjustments to the robot definition, USD structure, or your workflow between when it last worked and now, let us know—especially if you switched Isaac Sim versions or changed your authoring/export pipeline.
We noticed that this topic hasn’t received any recent responses, so we are closing it for now to help keep the forum organized.
If you’re still experiencing this issue or have additional questions, please feel free to create a new topic with updated details. When doing so, we recommend mentioning or linking to this original topic in your new post—this helps provide context and makes it easier for others to assist you.
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