Articulation Initialisation Error when loading scene with two policy controller robots

[SMEAC]

Description

When loading scene (interactive example) with two robots both using seperate policies, an error occurs in the initialisation, whereby all articulation joints in scene are found, and not per robot.

Two robots have been created with code from examples:

            self.go2 = Go2FlatTerrainPolicy(
            prim_path="/World/Go2",
            name="Go2",
            ##################
            usd_path="https://omniverse-content-production.s3-us-west-2.amazonaws.com/Assets/Isaac/5.1/Isaac/Robots/Unitree/Go2/go2.usd",
            ##################
            position=np.array([0, 0, 0.5]),
        )
        cabinet_prim_path = "/World/cabinet"
        cabinet_usd_path = get_assets_root_path() + "/Isaac/Props/Sektion_Cabinet/sektion_cabinet_instanceable.usd"

        cabinet_name = "cabinet"
        cabinet_position = np.array([0.8, 0.0, 0.4])
        cabinet_orientation = np.array([0.0, 0.0, 0.0, 1.0])

        stage_utils.add_reference_to_stage(cabinet_usd_path, cabinet_prim_path)

        self.cabinet = SingleArticulation(
            prim_path=cabinet_prim_path, name=cabinet_name, position=cabinet_position, orientation=cabinet_orientation
        )

        self.franka = FrankaOpenDrawerPolicy(
            prim_path="/World/franka", name="franka", position=np.array([0, -0, 0]), cabinet=self.cabinet
        )

Then performing the initialisation in on_physics_step(self, step_size):

            self.go2.initialize()
            self.franka.initialize()
            self.go2.post_reset()
            self.franka.post_reset()

The problem occurs inside the self.go2.initialize(), here all joints are found in the scene, not just the for the go2, this is seen in the log:
2026-05-08T22:51:25Z [221,319ms] [Warning] [isaacsim.robot.policy.examples.controllers.config_loader] panda_joint1 default position not found, setting to 0
2026-05-08T22:51:25Z [221,325ms] [Warning] [isaacsim.robot.policy.examples.controllers.config_loader]
panda_joint2 default position not found, setting to 0
2026-05-08T22:51:25Z [221,327ms] [Warning] [isaacsim.robot.policy.examples.controllers.config_loader]
panda_joint3 default position not found, setting to 0
2026-05-08T22:51:25Z [221,328ms] [Warning] [isaacsim.robot.policy.examples.controllers.config_loader]
panda_joint4 default position not found, setting to 0
2026-05-08T22:51:25Z [221,328ms] [Warning] [isaacsim.robot.policy.examples.controllers.config_loader] panda_joint5 default position not found, setting to 0
2026-05-08T22:51:25Z [221,328ms] [Warning] [isaacsim.robot.policy.examples.controllers.config_loader] panda_joint6 default position not found, setting to 0
2026-05-08T22:51:25Z [221,330ms] [Warning] [isaacsim.robot.policy.examples.controllers.config_loader] panda_joint7 default position not found, setting to 0
2026-05-08T22:51:25Z [221,331ms] [Warning] [isaacsim.robot.policy.examples.controllers.config_loader] panda_finger_joint1 default position not found, setting to 0
2026-05-08T22:51:25Z [221,332ms] [Warning] [isaacsim.robot.policy.examples.controllers.config_loader] panda_finger_joint2 default position not found, setting to 0

But then an error occurs, due to the tuples not being of the correct length for the loaded policies.

2026-05-08T22:51:25Z [221,334ms] [Error] [omni.kit.app._impl] [py stderr]: Traceback (most recent call last):
2026-05-08T22:51:25Z [221,335ms] [Error] [omni.kit.app._impl] [py stderr]: File "c:/isaac-sim/exts/isaacsim.examples.interactive/isaacsim/examples/interactive/quadruped/go2_withArm_example.py", line 187, in on_physics_step
2026-05-08T22:51:25Z [221,337ms] [Error] [omni.kit.app._impl] [py stderr]: self.go2.initialize()
2026-05-08T22:51:25Z [221,337ms] [Error] [omni.kit.app._impl] [py stderr]: File "c:/isaac-sim/exts/isaacsim.robot.policy.examples/isaacsim/robot/policy/examples/controllers/policy_controller.py", line 130, in initialize
2026-05-08T22:51:25Z [221,342ms] [Error] [omni.kit.app._impl] [py stderr]: self.robot._articulation_view.set_gains(stiffness, damping)
2026-05-08T22:51:25Z [221,342ms] [Error] [omni.kit.app._impl] [py stderr]: File "c:/isaac-sim/exts/isaacsim.core.prims/isaacsim/core/prims/impl/articulation.py", line 3044, in set_gains
2026-05-08T22:51:25Z [221,344ms] [Error] [omni.kit.app._impl] [py stderr]: stiffnesses = self._backend_utils.assign(
2026-05-08T22:51:25Z [221,344ms] [Error] [omni.kit.app._impl] [py stderr]: ^^^^^^^^^^^^^^^^^^^^^^^^^^^
2026-05-08T22:51:25Z [221,346ms] [Error] [omni.kit.app._impl] [py stderr]: File "c:/isaac-sim/exts/isaacsim.core.utils/isaacsim/core/utils/numpy/tensor.py", line 97, in assign
2026-05-08T22:51:25Z [221,347ms] [Error] [omni.kit.app._impl] [py stderr]: dst[tuple(indices)] = src
2026-05-08T22:51:25Z [221,348ms] [Error] [omni.kit.app._impl] [py stderr]: ~~~^^^^^^^^^^^^^^^^
2026-05-08T22:51:25Z [221,349ms] [Error] [omni.kit.app._impl] [py stderr]: ValueError: shape mismatch: value array of shape (12,) could not be broadcast to indexing result of shape (1,21)

Problem appears to be inpolicy_controller.py, the function self.robot.initialize(physics_sim_view=physics_sim_view) filing the variable name self.robot.dof_names, with all articulation joints in scene, not just the robot.
This leads to the variables being passed to
get_robot_joint_properties in policyController.py, passing all dof_names to the config_loader.py and single_articulation.py. Where the error occurs

Isaac Sim version

5.1.0

Operating System (OS)

Windows WSL Ubuntu 24.04, but also confirmed on normal Ubuntu 24.04.

GPU Name

RTX 5070

GPU Driver and CUDA versions

NVIDIA-SMI 591.44 Driver Version: 591.44 CUDA Version: 13.1

Logs

No response

Additional information

No response

[PeterL-NV]

Hi, thanks for the reporting. Here're some debugging tips for your issue:

1. Add this debug print right after creating the Go2 object

   self.go2 = Go2FlatTerrainPolicy(...)
   print(f"Go2 prim_path: {self.go2.robot.prim_path}")
   print(f"Go2 regex_paths: {self.go2.robot._articulation_view._regex_prim_paths}")

   This will confirm whether the articulation root was correctly resolved to /World/Go2/base.
2. If the articulation root was not correctly resolved, try explicitly passing root_path to your Go2 class:

   self.go2 = Go2FlatTerrainPolicy(
       prim_path="/World/Go2",
       root_path="/World/Go2/base",  # explicit articulation root
       name="Go2",
       ...
   )

3. Try replacing Go2 with Spot (it's the closest built-in quadruped) + Franka in the same scene to see if it's Go2-specific or a general multi-robot issue.

[SMEAC]

The output of the print statements gives correctly /World/Go2/base

Go2 prim_path: /World/Go2/base

Go2 regex_paths: ['/World/Go2/base']

The explizit setting of the root path, seems to make no difference.

Placing the Franka into the Spot scene, this seems to work fine, so it could be a Go2 problem.

The only difference that I can see, that could be causing an issue here, is the placement of the articulation root in the robots.
For Spot, the Articulation Root is at /World/Spot <-- base level of robot
For Go2, the Articulation Root is at /World/Go2/base <-- one level into the robot.

[PeterL-NV]

Does the issue persist if you only have Go2 in the scene (no Franka/cabinet)?

[SMEAC]

No, I have been experimenting with the Go2 and the Franka seperately for a while, and never had problems with either of them on their own.

[PeterL-NV]

Is it possible to share a repro case so we can take a further look?