Failed to get articulation fixed tendon stiffness from backend

[n10518975]

I am currently testing a new USD file with a custom class for in hand objects manipulation based off the ShadowHand example. However, I am sitting on a new set of errors that I am unsure to solve:

File "~/.local/share/ov/pkg/isaac_sim-2022.2.1/exts/omni.isaac.core/omni/isaac/core/articulations/articulation_view.py", line 2748, in set_fixed_tendon_properties
    current_stiffnesses = self._physics_view.get_fixed_tendon_stiffnesses()
  File "~/.local/share/ov/pkg/isaac_sim-2022.2.1/kit/extsPhysics/omni.physics.tensors-104.2.4-5.1/omni/physics/tensors/impl/api.py", line 709, in get_fixed_tendon_stiffnesses
    raise Exception("Failed to get articulation fixed tendon stiffnesses from backend")

Exception: Failed to get articulation fixed tendon stiffnesses from backend

Set the environment variable HYDRA_FULL_ERROR=1 for a complete stack trace.
2023-09-27 15:55:50 [12,611ms] [Error] [omni.client.python] TypeError: 'NoneType' object is not callable

At:
 ~/.local/share/ov/pkg/isaac_sim-2022.2.1/kit/python/lib/python3.7/threading.py(348): notify
  ~/.local/share/ov/pkg/isaac_sim-2022.2.1/kit/python/lib/python3.7/threading.py(365): notify_all
  ~/.local/share/ov/pkg/isaac_sim-2022.2.1/kit/python/lib/python3.7/concurrent/futures/_base.py(523): set_result
  ~/.local/share/ov/pkg/isaac_sim-2022.2.1/kit/extscore/omni.client/omni/client/__init__.py(84): list_cb

~/.local/share/ov/pkg/isaac_sim-2022.2.1/python.sh: line 41: 10000 Segmentation fault      (core dumped) $python_exe "$@" $args
There was an error running python

I am unsure whether this issue is likely due to the provided USD file that is being read or this issue being from the setup of the object class. Is there a massive oversight for how I set my program up or is this a matter of incorrect USD instancing or needing to readjust the USD file?

[rthaker]

Hi @n10518975 - The error messages you’re seeing suggest that there might be an issue with the way your custom class is interacting with the physics system, specifically with the fixed tendon properties of the articulation. The “Failed to get articulation fixed tendon stiffnesses from backend” error indicates that the physics system is unable to retrieve the stiffness properties of the tendons in your articulation. This could be due to the tendons not being properly set up in your USD file or in your custom class.

The “TypeError: ‘NoneType’ object is not callable” error suggests that a function or method is being called on a None object somewhere in your code. This could be due to an object not being properly initialized or a return value not being checked before being used.

The segmentation fault at the end is a more serious error that typically indicates an attempt to access memory that the program doesn’t have permission to access. This could be due to a bug in your code, but it could also be due to a bug in the underlying libraries or even in the Python interpreter itself.

Without more information about your custom class and the specifics of your USD file, it’s hard to provide a more specific diagnosis. However, here are a few things you could try:

1. Check the setup of your articulation in your USD file. Make sure that all the required properties for the tendons are properly set up.

2. Check your custom class for any places where you’re calling a method or function on an object. Make sure that the object is properly initialized and not None before calling the method or function.

3. Try running your code with a different version of Python or on a different machine to see if the segmentation fault still occurs. This could help you determine whether the issue is with your code or with your environment.

[n10518975]

Hey @rthaker ! I’ve given a looked into my USDA file and attempted to diagnose the issue with a comparison of the ShadowHand USDA, and I posted my findings here if that helps.

Adding physxTendon to revolute joints in a custom USDA for a manipulator

Hello! I was trying to find the solution for Failed to get articulation fixed tendon stiffness from backend and I I think I may have found the root problem to this error I was receiving for not grabbing backend tendon. I decided to look at my USD files as USDA and compare to the shadow hand example, and I think the last of physxTendon in my custom USD is the conflict . As an example of what I mean, here is the two same joints compared side by side - left is from my custom robot and the right i…

However if this isn’t enough or isn’t the solution I am happy to send the USD file via email if possible.

[rthaker]

Hi @n10518975 - I see the other post was answered by Ales. I hope your issue is resolved. Let me know if it’s not.

[n10518975]

Hey @rthaker ! I finally resolved the issue with the fixed tendon stiffness. I added the custom values and tested with the values from the ShadowHand example. The rest of the program was just adjusting the appropriate configs and some views and now the custom robot is working. Thank you and @AlesBorovicka for the help with resolving this issue.