Robot model in Isaac Sim falls apart


I am trying to follow this tutorial and this tutorial and apply them to my own two-wheeled robot (which I can’t show due to privacy reasons) so that it can move. I eventually want to make it move via keyboard. However, my robot falls apart when I press play, even after putting the body and wheels into a parent prim. One wheel and the body are on the floor, and one wheel just hangs in the air. Would anyone know what I can do to remedy this? Thanks.

please check to see if all joints and physics properties are set correctly

Edit: The below problem is solved, I unchecked ‘Fix Base Link’ in the URDF importer XD.

Thanks, I adjusted location of the revolute joints and I can manage to get the wheels to turn properly.

However, I cannot manage to get the robot to move. It stays in the same place even when the wheels are turning. It does not even fall in mid air - the physicsScene has gravity enabled and the RigidPrims do not have gravity disabled. I have done the following steps so far:

  1. Import the following URDF file using URDF importer (with default settings I think):
    robot_2.urdf (2.1 KB)

  2. Changed the axis of the revolute joints to the Z axis.

  3. Adjusted Local Positions 0 and 1 of the joints so they align with the axle of the wheel, adjusting Local Positions 0 so that they are at the center of the wheel, and Local Positions 1 so that they are between their respective wheel and the center of the robot, but closer to the center. (I have also tried to adjust Local Positions 0 so that they are touching the wheel, to similar results)

  4. Changed Local Rotation 0 to 90, 0, 0 and Local Rotation 1 to 0, 0, 0 for both joints.

  5. Ran the following code in the Script Editor: (3.3 KB)

  6. Pressed Play and attempted to move the robot.

I have tried to adjust inertia and mass to different values in the URDF file (not sure if to the right ones), and also tried to play around with other settings. I’m not sure what to do next, would you know what the problem is? Thanks.

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