How to create a closed-loop (ring) leaf structure with rigid “weld” in Articulation?

Omniverse Isaac Sim
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1

Hi all,

I’m trying to model a plant leaf with four connected rigid parts in Isaac Sim using USD/PhysX Articulation.
The structure is like a “ring” (closed-loop):

  • Leaf1 connects to Leaf2 by a hinge joint
  • Leaf2 connects to Leaf3 by a hinge joint
  • Leaf3 connects to Leaf4 by a hinge joint
  • Leaf4 should connect back to Leaf1 with a rigid “weld” (distance constraint, or fixed joint)

My current setup:

  • I use Articulation (chain of hinge joints) for all leaves
  • I tried to add a DistanceJoint (or FixedJoint) between Leaf4 and Leaf1 to form a closed loop

Issue:

  • PhysX reports: Articulation cannot contain a distance joint! (Please exclude it from articulation)
  • If I use only Articulation joints, I cannot create a “ring” because articulation must be tree-shaped

Questions:

  1. What is the recommended way to “weld” (rigidly connect) two non-parent/child links (e.g., Leaf1 and Leaf4) in the same Articulation, forming a closed-loop, in Isaac Sim/PhysX?
  2. Is there any official workaround to create a “closed kinematic loop” or “ring” structure in articulation?
  3. If not possible in Articulation, is there any other PhysX-supported mechanism in Isaac Sim to achieve this kind of loop with strict distance or rigid constraint?

Notes:

  • I do not want the “soft” constraint; it should be as rigid as possible, like a true weld.
  • Using PhysxSchema is not an option on my current setup.

Any advice, sample code, or official documentation reference would be appreciated!

Thanks!