OmniGraph Warning "NoneTygpe" Object has no attribute "is_homogeneous"

When I was configuring my Jackal 4 wheeled robot in Isaac Sim with ROS. A question arised: When I configure the Omni Graph for my 4 wheeled Jackal AGV in Isaac Sim, the default Articulation Root is the root of the USD(the top level Prim in Isaac Sim, here is World/Jackal) model, but it is wrong in the tf tree. But under this configuration the Omni Graph can subscibe the geometry/Twist msg from ROS and successfully transform the msg to wheel speeds of 4 wheels. But when I set the Articulation Root to base_link(correctly in URDF), the Omni Graph failed to transform the Twist to wheel speeds. The simulator says
OmniGraph Warning “NoneTygpe” Object has no attribute “is_homogeneous”
here is my 4 wheel robot cmd_vel Graph:


here is the model hierarchy:
jackal_conrfig
here is the 4 revolute joints of Jackal:
jackal_revolute_joints
How to solve this Problem?

Hi !

Were you able to solve the issue ?

Based on my experience, the issue is likely related to the descriptions in your URDF file. For instance, you might have set the type of the wheels to ‘fixed’ when they should actually be set to ‘continuous’.

I am also experiencing this issue with the Robots from the Isaac Assets. If you look at the startup console window, you may see a different message than the “NoneType” message. For example, I see the same “NoneType” message on the ArticulationController in the OmniGraph, but in my console is this error:

2024-07-12 22:41:46 [1,036,231ms] [Warning] [omni.physx.tensors.plugin] Failed to find articulation at '/World/jetracer'
2024-07-12 22:41:46 [1,036,231ms] [Error] [omni.physx.tensors.plugin] Pattern '/World/jetracer' did not match any articulations