Failed to load model use robot navigation

I’m a beginner in Isaacsim and I have a robot model right now converted from stp to USD.
My task is to make the robot move in a specific scene, I added articulation root, rigid body, joints, and mass to the model according to the tutorial, and I think there should be no problem with the above steps.
After I add the angular driver, the demo video is below.

However, loading the model fails.

I referenced some examples in isaacsim, but my robot and the examples are very different in structure.
My robot has a more complex structure, it doesn’t have a simple body and wheel structure like the example.
my question is:

  1. What is the reason for the loading failure and how to fix it?
  2. After stp is converted to usd, why can’t xform be selected as a group (I want to artificially select several parts of the body as one Xform, and make this whole as chassis).

I really need some help or workable ideas, thank you very much!!!

Thank you for your interest in Isaac Sim!

  1. what happens if you drag and drop your asset from he content browser to the stage tree? this should be a ui way of adding your asset as a reference to the stage.
  2. USD components are added on a tree hierarchy. while it doesn’t necessarily "select"all children when you select a parent, for the purposes I believe you are trying, if you use the parent of a collection of components, it should behave as a whole unit. (for instance if you add the Rigid Body API to the parent, all internal components will be included as part of the same rigid body)

You can also import your asset into onshape, then follow the onshape importer to convert your asset using the automated physics setup

@rgasoto Hello! thank you for your reply.
I desperately need your help! I’ve been converting my models using Onshape as you suggested for a while now, and since I haven’t used Onshape before, it took me some time to learn how to use it.
After I successfully converted my model with onshape, the exciting thing is that I managed to make my robot model move on the plane. Next, I still plan to import the model into Robot Navigation, but the problem reappears, as shown in the figure below.

Could you please explain to me what these four errors mean? thank you very much!
Following your suggestion and the example of the Transporter robot, I modified the converted model into the following structure,

It has the same structure as the transporter example, but the result is not as expected.
Also, due to the complex structure of my model (actually on the Onshape structure list, I see it has 207 parts), I followed the transporter example and selected all but the six wheels as the chassis, as follows as shown

Is this related to the error message?
Finally, the code sample I used is shown in the image below.

I really look forward to your reply, this problem has been bothering me for too long, I feel like I still can’t get to the point, thank you in advance for your reply!

for the wheel joints (Revolute_6 and Revolute_5 - from what I can see in the script), did you set up the joint Drive?
next, can you confirm that the robot is being found by the path defined in the final scene?

Some sort of video of the issue would help us understand what’s the cause of it.