[Question] Is it possible to simulate a conveyor belt in IsaacLab for RL training?

[sudoku77]

Hello IsaacLab team,

I would like to create a dynamic task in IsaacLab for RL training.
In this task, I need to use a conveyor belt that actively moves and transfers its motion through friction to a cube placed on it, so that the cube also moves along with the belt.

However, from what I see, the RigidBody class in IsaacLab does not seem to support modeling a conveyor belt or allowing a rigid body to move by itself (without being driven by joints or external forces).

Is there a recommended way to achieve this kind of environment setup in IsaacLab?

Thanks!

[RandomOakForest]

Thank you for posting this. To create a dynamic conveyor belt that transfers motion via friction to a cube in IsaacLab, you’re correct that the RigidBody abstraction (which typically represents static shapes or objects moved via joints or applied forces) doesn’t directly provide conveyor-like self-motion out of the box. Below, there is an approach to consider and some resources for your review.

I'll move this post to our Discussions section for the team and others to follow up.

Apply a Surface Velocity to the Conveyor Belt

The standard method—also used in Isaac Sim and Omniverse—is to use a collider with a surface velocity. Instead of animating the conveyor geometry, you define a static or kinematic plane (the belt’s surface), then apply a tangential surface velocity at the collider level. Physics engines (including those underlying Isaac Sim) treat any objects in contact with this collider as if the surface is moving, properly transferring frictional motion.

How To Do This in IsaacLab

• Create the conveyor belt as a static or kinematic rigid body (does not move via translation, just provides collision).
• Set the surface velocity parameter of the collider representing the belt’s upper surface.

Sample code snippet:

from omni.isaac.lab.sim.physics import set_collider_surface_velocity

# Assume `env` is your IsaacLab task environment
# Assume `belt_prim_path` is the path to your belt collider in the stage

surface_velocity_vector = [0.5, 0, 0]  # Moves along +X at 0.5m/s
set_collider_surface_velocity(
    stage=env.stage,               # or sim.stage depending on your initialization
    prim_path=belt_prim_path, 
    velocity=surface_velocity_vector
)

• This function will need to be called once during environment setup.
• For non-uniform belts, you can tile smaller collider sections with different velocities.

Resources

1. Conveyor Belt Setup & Surface Velocity

• Conveyor Belt Utility Documentation:
  https://docs.isaacsim.omniverse.nvidia.com/5.0.0/digital_twin/warehouse_logistics/ext_isaacsim_asset_gen_conveyor.html
  This page describes turning rigid bodies into functional conveyor belts, parameters for direction and velocity, and OmniGraph integration for dynamic tasks.¹
• Conveyor Belt Extension Node Reference (latest Isaac Sim):
  https://docs.isaacsim.omniverse.nvidia.com/5.0.0/py/source/extensions/isaacsim.asset.gen.conveyor/docs/ogn/OgnIsaacConveyor.html
  Describes conveyor-specific OmniGraph nodes and parameters such as velocity and animation.²

2. Setting Friction and Materials

• Physics Material Setup Tutorial (Isaac Sim):
  Tutorial: Assemble a Simple Robot – Isaac Sim Docs
  Includes how to assign and inspect physics materials, set static/dynamic friction, and tweak restitution settings on any mesh or collider (including conveyor belts).³
• Release Notes & Advanced Friction Modeling:
  Isaac Sim 5.0 Release Notes – Friction & Surface Velocity API
  This details friction models (Stribeck, enhanced surface velocity, splines for curved conveyors) and interface changes relevant for Isaac Sim 5.0 and later.⁴

3. Example Tutorials

• Video: Conveyor Belt Tool Setup in Omniverse Isaac Sim
  YouTube: Conveyor Belt Setup
  Shows step-by-step creation, velocity setting, and friction tuning for belt and cube assets in Isaac Sim UI and Action Graph system.⁵

Footnotes

1. https://docs.isaacsim.omniverse.nvidia.com/5.0.0/digital_twin/warehouse_logistics/ext_isaacsim_asset_gen_conveyor.html ↩

2. https://docs.isaacsim.omniverse.nvidia.com/5.0.0/py/source/extensions/isaacsim.asset.gen.conveyor/docs/ogn/OgnIsaacConveyor.html ↩

3. https://docs.isaacsim.omniverse.nvidia.com/latest/robot_setup_tutorials/tutorial_intro_assemble_robot.html ↩

4. https://docs.isaacsim.omniverse.nvidia.com/latest/overview/release_notes.html ↩

5. https://www.youtube.com/watch?v=NjfDcdlwHv0 ↩

[sudoku77]

Thank you for your prompt reply, your explanation was very clear. I am now able to use a collider with a surface velocity in the UI to simulate the conveyor belt functionality.

However, I would like to know how this can be implemented directly in IsaacLab through code. I am using the latest version of IsaacLab, but I could not find the function set_collider_surface_velocity (e.g., from omni.isaac.lab.sim.physics import set_collider_surface_velocity does not work).

I also tried another approach: pre-creating the conveyor belt as a static or kinematic rigid body in USD, setting the surface velocity parameter of the collider there, and then importing it through code as follows:

@configclass
class ConveyorSceneCfg(InteractiveSceneCfg):  
    # Table
    conveyor_belt = AssetBaseCfg(
        prim_path="{ENV_REGEX_NS}/Table",
        init_state=AssetBaseCfg.InitialStateCfg(pos=[-0.036, 0.166, 0.095], rot=[0.70711, 0.70711, 0, 0]),
        spawn=UsdFileCfg(usd_path=f"{Conveyor_PATH}"),
    )  

But in this case, the surface of the conveyor belt does not actually move after loading.

Is there a recommended way to achieve this behavior via code in IsaacLab?

Thanks again!

[HOCC493]

Hey did you find a solution?

[sudoku77]

Not yet

[HOCC493]

I got it working by bypassing the conveyor extension and directly running the velocity commands. I had Claude Code summarize it:

Hey! Got the conveyor physics working in Isaac Lab - turns out PhysX surface velocity only works with specific settings:

1. Must use CPU physics mode (use_fabric=False, device="cpu")
2. Conveyor plane needs to be a kinematic rigid body - static bodies don't work
3. Apply APIs in correct order: CollisionAPI → MeshCollisionAPI → RigidBodyAPI → PhysxSurfaceVelocityAPI
4. Disable GPU dynamics on the physics scene (physx_scene.CreateEnableGPUDynamicsAttr(False))

The key insight was that surface velocity is incompatible with GPU/Fabric physics - it's a CPU-only feature. Once we forced USD mode and CPU device in the SimulationCfg, blocks started moving perfectly at the configured 35mm/s.

I spawned a plane and a block and manually applied

`Apply surface velocity API to the plane
  PhysxSchema.PhysxSurfaceVelocityAPI.Apply(conveyor_prim)
  surface_velocity = PhysxSchema.PhysxSurfaceVelocityAPI(conveyor_prim)

  Set the actual velocity vector
  velocity = Gf.Vec3f(0.0, -0.035, 0.0)  # 35mm/s in -Y direction
  surface_velocity.CreateSurfaceVelocityAttr(velocity)
`

And that worked

[sudoku77]

Thank you, Yes it works!

[HOCC493]

Lmk if you find a solution that works with fabrix/gpu physics : /