[Question] number of physics material exceed 64K

[xindonglin99]

What's the correct way to spawn the same assets with different prim path?

I'm trying to spawn 20 cubes in each environment as stepping stones. This is the code that I'm using

def create_step_cfg(num_steps: int, size: Tuple[float, float, float]) -> RigidObjectCollectionCfg:
    """Create a step configuration."""
    collection = {}
    spawn_cfg = sim_utils.CuboidCfg(
        size=size,
        rigid_props=sim_utils.RigidBodyPropertiesCfg(kinematic_enabled=True),
        collision_props=sim_utils.CollisionPropertiesCfg(collision_enabled=True),
        visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.1, 0.1, 0.1), metallic=0.2),
        physics_material=sim_utils.RigidBodyMaterialCfg(
        friction_combine_mode="average",
        restitution_combine_mode="average",
        static_friction=1.0,
        dynamic_friction=1.0,
        restitution=0.0,
        ),
    )
    initial_state = RigidObjectCfg.InitialStateCfg()

    for i in range(num_steps):
        key = "step_" + str(i)
        current_prim_path = "/World/envs/env_.*/" + key 
        collection[key] = RigidObjectCfg(
            prim_path=current_prim_path,
            spawn=spawn_cfg,
            init_state=initial_state,
            collision_group=0,
            debug_vis=False,
    )

        
    return RigidObjectCollectionCfg(rigid_objects=collection)

in _setup_scene(self), I just do

self.steps = RigidObjectCollection(self.cfg.steps)

However, it seems for each stepping stone, one new physics material is created. And there's an error saying the number of physics materials exceeds the limit 64K. I would like to ask what is the correct way of creating one physics material and reusing it for every rigid object in the rigid object collection.

Also, I wonder if I'm using RigidObjectCollection in the correct way as every rigid object in it is technically the same but just with different prim paths. Any suggestions on this are appreciated!

[RandomOakForest]

Thanks for posting this. It seems including physics_material may be a causing this. Could you remove it from your parameters for CuboidCfg and try again? Thanks.

[xindonglin99]

Hi @RandomOakForest ,

Yes, removing the attribute physics_material can solve the issue. However, what if I want to apply a specific amount of friction to this cube? How can I do that?

Thanks for the reply!

[xindonglin99]

@RandomOakForest Sorry to ping you again. Is there any update on this? Any suggestions are appreciated.

[RandomOakForest]

Thanks for following up. So far I have confirmed that there is such a limit, however it should be really hard to reach it. If you use a small number of environments, do you still see the issue? Alternatively, it seems the for-loop in your code may be redone following this tutorial on spawning multiple assets. I'll post here if I have new findings.

[RandomOakForest]

I'm moving this issue to our Discussions section for follow up.

[xindonglin99]

@RandomOakForest , thanks for replying! I have no issue if I comment out the

physics_material=sim_utils.RigidBodyMaterialCfg(
        friction_combine_mode="average",
        restitution_combine_mode="average",
        static_friction=1.0,
        dynamic_friction=1.0,
        restitution=0.0,
        ),

However, I wonder if there's a way I can still assign a physics material to the rigid body. I only need 1 physics material, but if I put it in the above form, it seems it'll create one for each rigid body, even though these physics materials have the same properties. Is there a way that I can first create one physics material and bind it to the rigid body later? Should I do it before the cloner of the InteractiveScene or should I bind it afterwards for every environment manually?

Thanks a lot!

[RandomOakForest]

Thanks for following up. This can be done following this exmple in the Isaac Sim docs. Let us know if you need further help.

[xindonglin99]

It seems the link cannot be opened. Could you double check the link? Thanks!