Failed to add root joint of ArticulatedRoot type

Hi NVIDIA, @Hammad_M

So with Isaac Sim 2020.2, I have been trying to put the ArticulationAPI component into a robotic finger. I followed the guide here:

, adding a root_joint with type as ArticulatedJoint.
I clicked Play then the whole robot falls down out of gravity, then I set root_joint type as ArticulatedRoot type, the Sim just crashed.
Here is my USD file:

Could you give it a try?

Thank you!

Hi @Tadinu

Does this model have a URDF description file?
If it is the case, Could you share it?


Yes, here it is, which embeds ur10’s urdf into itself:

and the whole package here if you might need:

The model I’m using is actually part of the URDF that I generated from xacro files from this repo:

The meshes are converted to obj/fbx to be importable into Isaac.

Hi @Tadinu

I played a little to find an answer to your main question but I could not get any results.

Then, I isolated the finger from the ur10srh.urdf and everything works after that.
Also, I isolated a finger from shadow-robot/sr_common to test some things. It is works too… (see the images below and the importer configuration I used)

I am sharing in this link both isolated URDFs with the meshes and the USDs.

I hope it helps you… :)

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Thanks a lot for your help!
It indeed works that way. So I suppose during the process of urdf importing, the Sim might have done some required configuration to facilitate the later articulation API adding.
What I did is just isolating the finger by editing the whole USD on stage directly, which might have missed that essential configuration I guess.

Besides, I would like to suggest some user functions like:
(1) It looks like if the prim’s USD miss some field, it is currently not shown under Details or PhysXProperties panel. (For example, when one of robot joints does not have axis inside its USD, the Sim would complain about it with error log but there is no warning inside the Editor)
-> It might help to still display the field, though with an empty value, so we could notice then be able to configure it.

(2) If a joint’s relative body paths are incorrect, there seems to be no suggestion of its status as selecting the joint, also the relative paths are not editable. I had to save the whole stage to usda to be able to edit it.

(3) It would be great to have the URDF Importer panel allow importing from an external package folder in the drive, instead of only from Builtin URDF at ISAAC_SIM/_build/linux-x86_64/release/data/urdf.

(4) Last but not least, it might be really helpful if we have joint value slider inside the editor, so we could intuitively test if its joint axis and upper/lower limitation are correct

Thank you very much again for your quick support!

Thanks Tadinu for your thorough suggestions.
We will try to include them in our next release.


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[1] Will make sure this is resolved for the next release
[2] For the current public release there is a usd relationship editor under Window->isaac->relationship editor. This tool allows you to edit any relationship, so if you click on a joint you can modify the prims it links to

This should be a part of the main detail/properties panel in the next release
[3] Will make sure this is resolved for next release
[4]Joint limits can be edited in the details or properties panel, would this answer that specific comment or would there be additional features to make this a but more intuitive?

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Hi @Hammad_M,

Thanks for your info and confirmation regarding the updates in the next release, that would be great!
I didn’t actually know about (3).
For point (4), I would suggest both geometrical (and if possible physical at run-time, after clicking Play) representation of link movements.
Similarly to Rviz, I mean when we specify the value or just move the joint value slider, it would be really intuitive if we could see the joint movement and its limits being manifested by the connecting links itself in real-time (along with the current joint value visual aid).