Failed to execute a command: URDFImportRobot

esteban.lopez1 · October 14, 2025, 7:51am

Isaac Sim Version

5.0.0

Operating System

Windows 11

GPU Information

Model: RTX A3000
Driver Version: 573.73

Topic Description

The import function is unable to import any robot from isaac_sim.robot_motion.motion_generation/motion_policy-configs/…

When the urdf is selected a warning shows:

For universal_robots/ur3e I get

Steps to Reproduce

Click Import
Navigate to any of the subfolders of: C:/isaacsim/exts/isaacsim.robot_motion.motion_generation/motion_policy_configs/
Click ‘Load’

Error Messages

2025-10-14T07:48:48Z [1,092,474ms] [Warning] [isaacsim.asset.importer.urdf] link panda_face_back_left has no body properties (mass, inertia, or collisions) and is being merged into panda_hand
2025-10-14T07:48:48Z [1,092,474ms] [Warning] [isaacsim.asset.importer.urdf] link panda_face_back_right has no body properties (mass, inertia, or collisions) and is being merged into panda_hand
2025-10-14T07:48:48Z [1,092,474ms] [Warning] [isaacsim.asset.importer.urdf] link panda_face_left has no body properties (mass, inertia, or collisions) and is being merged into panda_hand
2025-10-14T07:48:48Z [1,092,474ms] [Warning] [isaacsim.asset.importer.urdf] link panda_face_right has no body properties (mass, inertia, or collisions) and is being merged into panda_hand
2025-10-14T07:48:48Z [1,092,474ms] [Warning] [isaacsim.asset.importer.urdf] link panda_leftfingertip has no body properties (mass, inertia, or collisions) and is being merged into panda_leftfinger
2025-10-14T07:48:48Z [1,092,475ms] [Warning] [isaacsim.asset.importer.urdf] link panda_rightfingertip has no body properties (mass, inertia, or collisions) and is being merged into panda_rightfinger
2025-10-14T07:48:48Z [1,092,475ms] [Warning] [isaacsim.asset.importer.urdf] link panda_hand has no body properties (mass, inertia, or collisions) and is being merged into panda_link8
2025-10-14T07:48:48Z [1,092,475ms] [Warning] [isaacsim.asset.importer.urdf] link right_gripper has no body properties (mass, inertia, or collisions) and is being merged into panda_link8
2025-10-14T07:48:48Z [1,092,475ms] [Warning] [isaacsim.asset.importer.urdf] link panda_link8 has no body properties (mass, inertia, or collisions) and is being merged into panda_link7
2025-10-14T07:48:48Z [1,092,475ms] [Warning] [isaacsim.asset.importer.urdf] link panda_wrist_end_pt has no body properties (mass, inertia, or collisions) and is being merged into panda_link7
2025-10-14T07:48:48Z [1,092,475ms] [Warning] [isaacsim.asset.importer.urdf] link panda_link0 has no body properties (mass, inertia, or collisions) and is being merged into base_link
2025-10-14T07:50:29Z [1,193,614ms] [Warning] [isaacsim.asset.importer.urdf] No mass specified for link base_link
2025-10-14T07:50:29Z [1,193,616ms] [Warning] [isaacsim.asset.importer.urdf] ROS_PACKAGE_PATH not defined, will skip checking ROS packages
2025-10-14T07:50:29Z [1,193,617ms] [Warning] [isaacsim.asset.importer.urdf] Path: package://franka_description/meshes/visual/link0.dae not found
2025-10-14T07:50:29Z [1,193,617ms] [Warning] [isaacsim.asset.importer.urdf] Failed to resolve mesh ‘package://franka_description/meshes/visual/link0.dae’
2025-10-14T07:50:29Z [1,193,617ms] [Warning] [isaacsim.asset.importer.urdf] Prim /visuals/base_link/link0 not created
2025-10-14T07:50:29Z [1,193,621ms] [Warning] [isaacsim.asset.importer.urdf] ROS_PACKAGE_PATH not defined, will skip checking ROS packages
2025-10-14T07:50:29Z [1,193,621ms] [Warning] [isaacsim.asset.importer.urdf] Path: package://franka_description/meshes/collision/link0.stl not found
2025-10-14T07:50:29Z [1,193,621ms] [Warning] [isaacsim.asset.importer.urdf] Failed to resolve mesh ‘package://franka_description/meshes/collision/link0.stl’
2025-10-14T07:50:29Z [1,193,621ms] [Warning] [isaacsim.asset.importer.urdf] Prim /colliders/base_link/link0 not created
2025-10-14T07:50:29Z [1,193,624ms] [Error] [omni.kit.commands.command] Failed to execute a command: URDFImportRobot.
File “c:/isaacsim/exts/isaacsim.asset.importer.urdf/isaacsim/asset/importer/urdf/impl/extension.py”, line 426, in check_callback
self.start_import(checked=True, path=path)
File “c:/isaacsim/exts/isaacsim.asset.importer.urdf/isaacsim/asset/importer/urdf/impl/extension.py”, line 472, in start_import
self._load_robot(dest_path, path)
File “c:/isaacsim/exts/isaacsim.asset.importer.urdf/isaacsim/asset/importer/urdf/impl/extension.py”, line 586, in _load_robot
omni.kit.commands.execute(
File “c:/isaacsim/extscache/omni.kit.commands-1.4.10+8131b85d.wx64.r.cp311/omni/kit/commands/command.py”, line 463, in execute
result = omni.kit.undo.execute(command, name, kwargs)
[…skipped…]
File “c:/isaacsim/extscache/omni.kit.commands-1.4.10+8131b85d.wx64.r.cp311/omni/kit/undo/undo.py”, line 78, in execute
result = _execute(command, name, level, history_key)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File “c:/isaacsim/extscache/omni.kit.commands-1.4.10+8131b85d.wx64.r.cp311/omni/kit/undo/undo.py”, line 459, in _execute
raise error
File “c:/isaacsim/extscache/omni.kit.commands-1.4.10+8131b85d.wx64.r.cp311/omni/kit/undo/undo.py”, line 420, in _execute
result = command.do()
^^^^^^^^^^^^
File “c:/isaacsim/exts/isaacsim.asset.importer.urdf/isaacsim/asset/importer/urdf/impl/commands.py”, line 145, in do
return self._urdf_interface.import_robot(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

<class ‘RuntimeError’> Used null prim
2025-10-14T07:50:29Z [1,193,626ms] [Error] [omni.ui.python] RuntimeError: Accessed invalid null prim

At:
c:/isaacsim/exts/isaacsim.asset.importer.urdf/isaacsim/asset/importer/urdf/impl/extension.py(594): _load_robot
c:/isaacsim/exts/isaacsim.asset.importer.urdf/isaacsim/asset/importer/urdf/impl/extension.py(472): start_import
c:/isaacsim/exts/isaacsim.asset.importer.urdf/isaacsim/asset/importer/urdf/impl/extension.py(426): check_callback

Additional Information

What I’ve Tried

I have tried to load several different robots such as franka, Denso and Universal Robots using the URDFs.

I also have tried to set different Joint Configurations and Drive types.

Simplychenable · October 14, 2025, 8:34am

@esteban.lopez1 i am just another user, but don’t you need meshes along with the .urdf for the asset to be imported properly? we can test it by trying to import a custom urdf with proper structure and see if the same issue persists.

and, just wanted to point out, the robots that came with Isaac Sim such as ur3e can be found within the Content browser:

esteban.lopez1 · October 14, 2025, 8:51am

Thanks for your reply and suggestions. My goal of is to be able to interact with the robot using the Lula Test Widget:

Which requires the meshes, urdf and yaml.

Your observation about the required meshes seems to be correct. It seems that URDFs may or may not contain mesh information?

I created my own URDF in blender (attached) and it did not have any issues while importing, however when it comes to simulating the robot moves, it fails, which is the foundamental reason why I tried to use a reference URDF to try to rule out the source of the issue being the urdf.

So bottom line is:
Why can I load my urdf but not nvidia’s?

shareable.zip (10.3 KB)

Simplychenable · October 14, 2025, 9:08am

i’ll be honest, i’ve not thought of that until now. but it looks like it’s by design:

VickNV · May 3, 2026, 4:32am

Hi @esteban.lopez1,

Thanks for reporting this, and apologies for the delayed response.

Root cause: The crash happens because your URDFs use package:// mesh paths (e.g. package://franka_description/meshes/collision/link0.stl), but ROS_PACKAGE_PATH is not set in your environment. On Windows without a ROS installation, Isaac Sim’s
URDF importer cannot resolve these paths — it fails to create the mesh prims, then crashes with Used null prim when it tries to reference them downstream.

The key log lines that confirm this:

  [Warning] ROS_PACKAGE_PATH not defined, will skip checking ROS packages                                                                                                                                                                          
  [Warning] Path: package://franka_description/meshes/collision/link0.stl not found                                                                                                                                                                
  [Warning] Failed to resolve mesh 'package://franka_description/meshes/collision/link0.stl'                                                                                                                                                       
  [Error] Failed to execute a command: URDFImportRobot                                                                                                                                                                                             
  RuntimeError: Used null prim

Why the bundled URDFs fail: The URDF files under motion_policy_configs/ are meant for motion generation configuration and reference meshes via ROS package:// paths. They aren’t self-contained — the importer needs to know where to find the
actual mesh files.

Workarounds for Isaac Sim 5.x on Windows (no ROS):

Use the pre-built USD assets instead. The robots you need (UR3e, Franka, Denso) are already available as USD in the Content browser under NVIDIA Assets → Isaac → Robots. These are ready to use with the Lula Test Widget without any URDF
import step.
If you need to import a URDF, rewrite the mesh paths from package:// to relative paths pointing to the actual mesh files on disk. For example, change:

  <mesh filename="package://franka_description/meshes/visual/link0.dae"/>

to:

  <mesh filename="meshes/visual/link0.dae"/>

and place the meshes/ folder next to your .urdf file.
3. Set ROS_PACKAGE_PATH manually (no ROS install required). In a terminal before launching Isaac Sim:

  set ROS_PACKAGE_PATH=C:\path\to\your\catkin_ws\src                                                                                                                                                                                             
  "C:\isaacsim\isaac-sim.bat"

The importer will then search that directory tree for the package folders.

Status in Isaac Sim 6.0: This workflow is resolved. The URDF importer was rewritten with explicit ROS package path support that no longer depends on environment variables:

GUI: A table widget in the import dialog lets you add package name + path rows directly
Standalone CLI: --ros-package franka_description:/path/to/franka_description (repeatable for multiple packages)
Python API: URDFImporterConfig(ros_package_ paths=[{“name”: “franka_description”, “path”: “/path/to/franka_description”}])

No ROS_PACKAGE_PATH environment variable needed.

hking · May 19, 2026, 4:42pm

Hello!

We noticed that this topic hasn’t received any recent updates from anyone reporting this issue, so we are closing it for now to help keep the forum organized.

If you are still experiencing this issue or have related questions, please create a GitHub Discussion or Issue in the Isaac Sim repository and include a link to this topic along with updated details. Mentioning or linking to this original topic provides helpful context and makes it easier for others to assist you.

Thank you for being part of the NVIDIA Isaac Sim community.

Best regards,
The NVIDIA Isaac Sim Forum Team

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