How to save collision mesh to a Blender-exported USD so it persists in Isaac Lab?

[rayrsys]

                                                                                                                                                                                                                                     Hi everyone,

I'm working on a chess manipulation environment in Isaac Lab where a G1 robot picks up and places chess pieces on a board. The chess board and pieces are exported from Blender as USD files.

The problem: My chess board USD has no collision — the robot's hands pass right through it. I can manually add a collision mesh in Isaac Sim (right-click → Add → Physics → Colliders), and it works perfectly. But the collision doesn't persist —
every time I reload the scene, I have to add it again.

What I've tried:

1. Adding rigid/collision props in the Isaac Lab spawn config:
   chess_board = AssetBaseCfg(
   prim_path="/World/envs/env_.*/ChessBoard",
   spawn=UsdFileCfg(
   usd_path="/path/to/chessboard.usdc",
   scale=(0.3, 0.3, 0.3),
   rigid_props=sim_utils.RigidBodyPropertiesCfg(kinematic_enabled=True),
   collision_props=sim_utils.CollisionPropertiesCfg(collision_enabled=True),
   ),
   )
   Result: No effect — the robot still passes through the board.

2. Adding mesh_collision_props with convex decomposition:
   mesh_collision_props=sim_utils.MeshCollisionPropertiesCfg(mesh_approximation="convexDecomposition")
   Result: MeshCollisionPropertiesCfg doesn't accept mesh_approximation parameter.

3. Exporting from Isaac Sim after manually adding collider (Export Selected):
   The exported USD file ends up at a completely different scale (~700 units vs the original ~2 units), so it doesn't load correctly back into the scene.

4. Adding physics in Blender before export (Rigid Body → Passive → Collision Shape → Mesh):
   Haven't confirmed if this translates to proper UsdPhysics.CollisionAPI in the exported USD.

My setup:

• Isaac Lab (from IsaacLab repo)
• Blender 4.x exporting to .usdc with "Convert to USD Preview Surface" enabled
• Chess board is ~2m across in Blender, scaled to 0.3 in Isaac Lab
• Board should be kinematic (doesn't move, but things collide with it)

What I need:
A reliable way to either:

• Export from Blender with collision baked into the USD
• Or programmatically add collision (with proper mesh approximation) that persists in the USD file
• Or configure Isaac Lab's spawn config to properly generate collision from the visual mesh

Has anyone successfully exported Blender models with working collision in Isaac Lab? What's the recommended workflow?

Thanks!

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