[Question] How to load custom articulation with joint into isaaclab

[lxy270]

hi, I am trying to load an articulation(simply a sphere with a D6 joint) into the scene, but I got the following error indicating the joint is not recognized, I wonder where could went wrong

the error I got:

Traceback (most recent call last):
  File "/home/xinyili/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/asset_base.py", line 92, in <lambda>
    lambda event, obj=weakref.proxy(self): obj._initialize_callback(event),
  File "/home/xinyili/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/asset_base.py", line 263, in _initialize_callback
    self._initialize_impl()
  File "/home/xinyili/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation.py", line 942, in _initialize_impl
    self._process_cfg()
  File "/home/xinyili/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation.py", line 1069, in _process_cfg
    indices_list, _, values_list = string_utils.resolve_matching_names_values(
  File "/home/xinyili/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/utils/string.py", line 364, in resolve_matching_names_values
    raise ValueError(
ValueError: Not all regular expressions are matched! Please check that the regular expressions are correct: 
	.*: []
Available strings: []

[INFO]: Setup complete...
Traceback (most recent call last):
  File "/home/xinyili/IsaacLab/3d_action.py", line 176, in <module>
    main()
  File "/home/xinyili/IsaacLab/3d_action.py", line 171, in main
    run_simulator(sim, scene)
  File "/home/xinyili/IsaacLab/3d_action.py", line 136, in run_simulator
    scene.reset()
  File "/home/xinyili/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/scene/interactive_scene.py", line 347, in reset
    articulation.reset(env_ids)
  File "/home/xinyili/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation.py", line 166, in reset
    for actuator in self.actuators.values():
AttributeError: 'Articulation' object has no attribute 'actuators'

I save the articulation in the isaacsim GUI by ‘save selected’ of the sphere and the joint where the sphere is set to be the articulation root, since I cannot upload usd file in the forum, here I attach the usda version of my articulation

#usda 1.0
(
    defaultPrim = "Root"
    upAxis = "Z"
)

def Xform "Root"
{
    def Sphere "Sphere" (
        apiSchemas = ["PhysicsArticulationRootAPI", "PhysxArticulationAPI", "PhysicsRigidBodyAPI", "PhysxRigidBodyAPI", "PhysicsCollisionAPI", "PhysxCollisionAPI"]
    )
    {
        float3[] extent = [(-0.5, -0.5, -0.5), (0.5, 0.5, 0.5)]
        bool physics:collisionEnabled = 1
        bool physics:kinematicEnabled = 0
        bool physics:rigidBodyEnabled = 1
        double radius = 0.5
        custom bool refinementEnableOverride = 1
        custom int refinementLevel = 2
        token ui:displayGroup = "Material Graphs"
        token ui:displayName = "Sphere"
        int ui:order = 1024
        float3 xformOp:rotateXYZ = (0, -0, 0)
        float3 xformOp:scale = (1, 1, 1)
        double3 xformOp:translate = (0, 0, 0)
        uniform token[] xformOpOrder = ["xformOp:translate", "xformOp:rotateXYZ", "xformOp:scale"]

        def PhysicsJoint "D6Joint" (
            apiSchemas = ["PhysicsLimitAPI:transX", "PhysicsLimitAPI:transY", "PhysicsLimitAPI:transZ", "PhysicsLimitAPI:rotX", "PhysicsLimitAPI:rotY", "PhysicsLimitAPI:rotZ"]
        )
        {
            float limit:rotX:physics:high = -1
            float limit:rotX:physics:low = 1
            float limit:rotY:physics:high = -1
            float limit:rotY:physics:low = 1
            float limit:rotZ:physics:high = -1
            float limit:rotZ:physics:low = 1
            float limit:transX:physics:high = -1
            float limit:transX:physics:low = 1
            float limit:transY:physics:high = -1
            float limit:transY:physics:low = 1
            float limit:transZ:physics:high = -1
            float limit:transZ:physics:low = 1
            rel physics:body1 = </Root/Sphere>
            float physics:breakForce = inf
            float physics:breakTorque = inf
            point3f physics:localPos0 = (0, 0, 0)
            point3f physics:localPos1 = (0, 0, 0)
            quatf physics:localRot0 = (1, 0, 0, 0)
            quatf physics:localRot1 = (1, 0, 0, 0)
        }
    }
}

the code I use to load the articulation:

class BouncingCfg(InteractiveSceneCfg):
    sphere = ArticulationCfg(
        prim_path="{ENV_REGEX_NS}/Sphere",
        # spawn=sim_utils.SphereCfg(
        spawn=sim_utils.UsdFileCfg(usd_path="/home/xinyili/IsaacLab/Sphere_joint.usd",
           rigid_props=sim_utils.RigidBodyPropertiesCfg(
               rigid_body_enabled=True,
               max_linear_velocity=1000.0,
               max_angular_velocity=1000.0,
               max_depenetration_velocity=100.0,
               enable_gyroscopic_forces=True,
           ),
           articulation_props=sim_utils.ArticulationRootPropertiesCfg(
               enabled_self_collisions=False,
               solver_position_iteration_count=4,
               solver_velocity_iteration_count=0,
               sleep_threshold=0.005,
               stabilization_threshold=0.001,
           ),
        ),
        init_state=ArticulationCfg.InitialStateCfg(pos=[0, 0, 1], lin_vel=[10, 0.3, 0]),
        actuators={
           "actuator": ImplicitActuatorCfg(
               joint_names_expr=["D6Joint"],
               effort_limit=400.0,
               velocity_limit=100.0,
               stiffness=0.0,
               damping=10.0,
           ),
        }
    )

def run_simulator(sim: sim_utils.SimulationContext, scene: InteractiveScene):
    sphere = scene["sphere"]
    sim_dt = sim.get_physics_dt()
    scene.reset()
    
    # Simulation loop
    while simulation_app.is_running():
        scene.write_data_to_sim()
        sim.step()
        scene.update(sim_dt)


def main():
    sim_cfg = sim_utils.SimulationCfg(device=args_cli.device, dt=0.01)
    sim = SimulationContext(sim_cfg)
    sim.set_camera_view([5, 0.0, 8], [0.0, 0.0, 2.0])
    scene_cfg = BouncingCfg(num_envs=args_cli.num_envs, env_spacing=20)
    scene = InteractiveScene(scene_cfg)
    sim.reset()
    run_simulator(sim, scene)

any help would be appreciated, thanks!

[RandomOakForest]

Thanks for posting this. There seems to be an issue with your saved articulation because you got Available strings: []. Can you confirm that you can open the newly saved assets you saved using "save selected" in Isaac Sim?

[jiangranlv]

I met the same issue

[RandomOakForest]

Following up, maybe using the latest release of Isaac Sim and Isaac Lab in a fresh install would help. Let us know if we can be of further help. If you still face this issue, please open a bug report. Thanks.

[omarrayyann]

I am facing the same issue.

[omarrayyann]

@lxy270 Did you figure this out?

[lozoRUST]

@lxy270 @jiangranlv @omarrayyann @RandomOakForest Facing the same problem. Have you solved this?

[RandomOakForest]

Following up, we are working on making this easier, as the D6 joint is not currently recognized by Isaac Lab's articulation loader, which expects supported joint types (such as revolute, prismatic, or fixed joints). When it fails to find any valid joints, the articulation object is not properly initialized, resulting in missing attributes like actuators and leading to the error you see.

What you can do:

• Replace the D6 joint with a supported joint type (e.g., PhysicsRevoluteJoint, PhysicsPrismaticJoint, or PhysicsFixedJoint) in your USD file if your use case allows.
• If you require multiple degrees of freedom, consider building your articulation using a chain of supported joints, each providing one or two degrees of freedom.
• After updating your USD, ensure that the joint names in your actuator configuration match the actual joint names in the USD hierarchy, and that the regular expressions in joint_names_expr correspond to those names.

[lozoRUST]

@RandomOakForest hi, but i'm wondering why other joints (PhysicsRevoluteJoint, PhysicsPrimaticJoint, PhysicsFixedJoint) are not recognized by the ImplicitActuatorCfg. Here's my post describing my problem.https://forums.developer.nvidia.com/t/joint-match-problems-in-scripts/337828