[Question] Contact reporter initialization fails

[HarrisonDeurwaarder]

Question

I use a contact sensor in my scene (It is attached to the articulation in the provided code, but the issues persists regardless of the parent prim), and have set activate_contact_sensors=True for several prims. I have also changed the parent prim with no success.

The exact error message is:
RuntimeError: Sensor at path '/World/envs/env_.*/Robot' could not find any bodies with contact reporter API.
HINT: Make sure to enable 'activate_contact_sensors' in the corresponding asset spawn configuration.

Has anyone encountered this issue before? If so, is there a fix? I've reviewed functional scripts using contact sensors, but I can't find the difference that is causing this.

scene_cfg.py

Build Info

• Isaac Lab Version: 2.3.0
• Isaac Sim Version: 5.1.0

[RandomOakForest]

Thank you for posting this. Two concrete issues in your snippet:

1. Your ContactSensorCfg.prim_path points at the articulation root ({ENV_REGEX_NS}/Robot), which is not itself a rigid body.
2. You only set activate_contact_sensors=True on the wall_* cuboids and via robot.spawn override, but the contact sensor still needs to resolve to rigid body prims (links) inside the Franka USD that have contact reporting enabled.¹²³⁴

1. Fix the contact sensor prim_path

Point the sensor to actual rigid body links of the Franka, not just /Robot:

contact_forces: ContactSensorCfg = ContactSensorCfg(
    prim_path="{ENV_REGEX_NS}/Robot/.*",   # or narrower, e.g. gripper or link names
    update_period=0.0,
    history_length=config.config['scene']['sensor']['force_history_length'],
    debug_vis=True,
)

Common choices (depending on link names in the USD) are:

• {ENV_REGEX_NS}/Robot/panda_link0
• {ENV_REGEX_NS}/Robot/panda_link[1-7]
• {ENV_REGEX_NS}/Robot/panda_hand
• Or a regex like {ENV_REGEX_NS}/Robot/panda_.* to cover all robot links.²⁵¹

The key requirement is: prim_path must match prims that are physics bodies with collision and the contact reporter API; otherwise you get exactly the RuntimeError you see.⁶¹²

2. Ensure contact sensors are enabled on the Franka USD

FRANKA_PANDA_HIGH_PD_CFG by default usually has activate_contact_sensors=False in its spawn=sim_utils.UsdFileCfg(...).³⁴
You are correctly overriding it:

robot: ArticulationCfg = FRANKA_PANDA_HIGH_PD_CFG.replace(
    prim_path="{ENV_REGEX_NS}/Robot",
    init_state=FRANKA_PANDA_HIGH_PD_CFG.init_state.replace(
        pos=(0.0, 0.0, thickness),
    ),
)
robot.spawn.activate_contact_sensors = True

That is the right pattern; just make sure this assignment executes after the replace call (as you have) and before the scene is built.⁷⁴³

3. Optional: filter against walls only

If you want the sensor to report contacts only between the robot and your walls, add a filter:

contact_forces: ContactSensorCfg = ContactSensorCfg(
    prim_path="{ENV_REGEX_NS}/Robot/.*",
    update_period=0.0,
    history_length=config.config['scene']['sensor']['force_history_length'],
    debug_vis=True,
    filter_prim_paths_expr=[
        "{ENV_REGEX_NS}/wallx1",
        "{ENV_REGEX_NS}/wallx2",
        "{ENV_REGEX_NS}/wally1",
        "{ENV_REGEX_NS}/wally2",
        "{ENV_REGEX_NS}/wallz1",
        "{ENV_REGEX_NS}/wallz2",
    ],
)

This is consistent with the official contact sensor examples, where the sensor is attached to specific robot bodies and optionally filtered to particular objects.¹⁶³

4. Quick sanity checks

• In the USD inspector, verify that the prims you target (e.g. /World/envs/env_0/Robot/panda_link1) have collision and are rigid bodies.
• Print the expanded expression to confirm it matches what you expect:

print(scene.cfg.contact_forces.prim_path)

• Start with a simple regex like {ENV_REGEX_NS}/Robot/panda_link7 and verify you get non-zero forces when that link hits a wall.⁸¹

Footnotes

1. https://isaac-sim.github.io/IsaacLab/main/source/overview/core-concepts/sensors/contact_sensor.html ↩ ↩² ↩³ ↩⁴ ↩⁵

2. https://isaac-sim.github.io/IsaacLab/main/source/api/lab/isaaclab.sensors.html ↩ ↩² ↩³

3. https://isaac-sim.github.io/IsaacLab/main/source/tutorials/05_controllers/run_osc.html ↩ ↩² ↩³ ↩⁴

4. https://forums.developer.nvidia.com/t/weird-behavior-in-franka-robot-when-no-input-command-during-simulation-in-orbit/292186 ↩ ↩² ↩³

5. https://isaac-sim.github.io/IsaacLab/main/source/tutorials/04_sensors/add_sensors_on_robot.html ↩

6. https://github.com/isaac-sim/IsaacLab/discussions/2026 ↩ ↩²

7. https://wavegit.mipt.ru/derryx/IsaacLab/-/blob/931679641ee84e1b4175c15b48f9286d44ba9b04/scripts/tutorials/05_controllers/run_osc.py ↩

8. https://forums.developer.nvidia.com/t/detect-collision-between-agents-and-obstacles-in-isaac-lab-scripts/306405 ↩

[HarrisonDeurwaarder]

I see the issues; thank you for your help!

[HarrisonDeurwaarder]

Unfortunately, the error persists no matter which prim I target in the path (I've targetted examples above as well as several regexes). I assume that setting the enable_contact_sensors flag trickles down to the rigid bodies, right? I not, I suspect that that is the issues, but otherwise I'm not sure.

[HarrisonDeurwaarder]

I actually believe that it's an issue with replicate_physics. In the meantime, the only solution that I can see is to disable it.

[RandomOakForest]

Following up, I'll move then this issue to our Discussions section for follow-up.