Create articulations on robot

Hi. I have a fairly complicated robot I would like to model using Isaac Sim. I have exported the model from CAD using a USD exporter and can see the robot, along with the correct hierarchy, in the editor. I have a few questions:

  1. The CAD model was done with Z down. This isn’t an option in Preferences > Stage > Default Up Axis. How can I set the Up axis to -Z?
  2. I can’t seem to get joints to function correctly. I’ve combed through videos and Isaac docs and have since gone in circles. The models’ hierarchy consists of many nested Xforms with the leaves of each Xform tree being a body. I would like to have Xform’s more towards the root be articulated, but I get errors saying that they are not bodies. The models at this point in the tree are also not convex, so the convex hull collision model approximation results in the model exploding. How can I articulate two Xforms without having them as bodies?
  3. The robot has a few linear screw actuators. Is a prismatic joint the best way to model these?
  4. The robot has many orthographic camera’s and I’ve noticed quite a few odd artifacts. Who should I send a bug report to?

It would be awesome if I could setup a meeting or have an email of someone to explain the questions in more detail. Thank you in advance for the help!

Hi Aaron, this is the best place to ask your questions. Because you can get answered by Isaac Sim team or community. If you don’t get your answer here please email me at

  1. Only Z up is supported. but you can set the gravity vector to point +Z if that would result in the same behavior. If you create a physics scene in your stage you can set gravity on that prim.
  2. An example USD file would be helpful
  3. Yes
  4. Screenshots and USD’s that can reproduce the issues would be helpful so we can file bugs with the appropriate teams