[Question] Unable to move object close to finger when attaching

[skyline111223]

Question

I’m trying to attach a deformable (or rigid) object between the Panda gripper’s fingers, but when I command it to move toward the fingers, it never gets close enough—it stops at a distance. Conversely, when I command it to move away from the gripper, it works fine.

cfg = DeformableObjectCfg(
    prim_path="{ENV_REGEX_NS}/Robot/left_finger",
    spawn=sim_utils.MeshCuboidCfg(
        size=(0.2, 0.2, 0.2),
        deformable_props=sim_utils.DeformableBodyPropertiesCfg(rest_offset=0.0, contact_offset=0.001),
        visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.5, 0.1, 0.0)),
        physics_material=sim_utils.DeformableBodyMaterialCfg(poissons_ratio=0.4, youngs_modulus=1e5),
    ),
    init_state=DeformableObjectCfg.InitialStateCfg(pos=(0.0, 0.0, 1.0)),
    debug_vis=True,
)

The object should move all the way into the gripper, contacting or passing between the fingers only if I change the init_state. Does anyone know what could prevent the object from fully reaching the fingers when it’s attached? Any advice on config parameters or attachment methods would be greatly appreciated.

[RandomOakForest]

Thank you for starting this post. I'll move it to our Discussions section for follow up. In the meantime, here are a few things to consider:

🔧 Collision Offset Configuration

1. Increase contact_offset
   Current setting (contact_offset=0.001) is likely too low. Raise it to 0.005-0.01 to ensure early collision detection:

deformable_props=sim_utils.DeformableBodyPropertiesCfg(
    rest_offset=0.0, 
    contact_offset=0.01  # Increased from 0.001
)

This allows collision detection to trigger earlier during approach¹².

2. **Adjust rest_offset**For precise contact, use a negative rest offset if collision shapes are larger than visual meshes:

rest_offset=-0.001  # Allows graphics shapes to touch

🕹️ Kinematic Control Adjustment

Instead of position commands, use velocity-controlled movement with force limits:

# Replace position targets with velocity control
target_velocity = torch.tensor([0.5])  # Movement speed (m/s)
cube_object.set_nodal_kinematic_target_velocity(target_velocity)

This prevents premature stopping due to resistance².

⚡ Simulation Parameters

Optimize physics stepping for deformables:

sim_cfg = sim_utils.SimulationCfg(
    dt=0.005,              # Reduced from 0.01
    substeps=4,            # Increased substeps
    solver_iterations=64   # Higher solver precision
)

Smaller timesteps improve deformable-rigid interaction stability³².

🎯 Attachment Verification

1. Confirm the object is directly parented to the finger joint in the USD hierarchy
2. Use debug_vis=True to visualize attachment points
3. Check for floating offsets using:

print(cube_object.data.nodal_positions_w)

Alternative Approach

If issues persist:

# Explicitly set nodal positions near fingers
gripper_pos = robot.data.ee_state_w[..., :3] 
nodal_positions = gripper_pos + torch.tensor([0, 0, -0.05])  # 5cm below gripper
cube_object.write_nodal_state_to_sim(nodal_positions)

Forces initial proximity to fingers³.

These adjustments address collision detection sensitivity, material properties, and control methods that prevent full approach. Start with contact_offset/rest_offset changes as they most directly impact proximity behavior¹².

References

Footnotes

1. https://docs.nvidia.com/gameworks/content/gameworkslibrary/physx/guide/Manual/AdvancedCollisionDetection.html ↩ ↩²

2. https://github.com/isaac-sim/IsaacLab/discussions/2651 ↩ ↩² ↩³ ↩⁴

3. https://isaac-sim.github.io/IsaacLab/main/source/tutorials/01_assets/run_deformable_object.html ↩ ↩²