Relative Differential IK: controlled-frame orientation drifts during sustained single-axis teleoperation, despite exactly-zero commanded rotation

[Amos25103]

Screen.Recording.2026-08-19.133109.mp4

Description

I am using a custom UR5 articulation with Isaac Lab's stock relative differential inverse kinematics controller and Se3KeyboardCfg.

During pure vertical keyboard teleoperation using the Q and E keys, the controlled frame moves along the requested Z direction, but its orientation does not remain vertical. The tool gradually tilts as the vertical motion continues.

The same teleoperation workflow appears to work fine maintain a straight tool orientation when using the built-in UR10 example:

./isaaclab.sh -p scripts/tools/record_demos.py \
    --viz kit \
    --livestream 2 \
    --device cpu \
    --task Isaac-Stack-Cube-UR10-Long-Suction-IK-Rel-v0 \
    --teleop_device keyboard \
    --dataset_file /workspace/datasets/ur10_demo.hdf5 \
    --num_demos 1
    
I would like to understand whether this behaviour indicates:

A problem with the UR5 USD articulation or joint-frame definitions
A Jacobian or coordinate-frame inconsistency
Expected behaviour from relative pose IK
A required robot-specific Differential IK configuration

I expect the controlled wrist_3_link frame to translate along Z while maintaining its current orientation.

In particular:

Q should produce positive Z translation
E should produce negative Z translation
The rotational part of the keyboard action should remain zero
The TCP or controlled-link orientation should remain approximately constant
Actual behavior

The UR5 moves in the requested Z direction, but the controlled-frame quaternion changes significantly during sustained Q or E input.

The main visible effect is that the wrist assembly does not remain vertically aligned during the motion.

Stock action configuration

The environment uses the stock DifferentialInverseKinematicsActionCfg. There is no custom action class, target latch, persistent Cartesian target, or monkey patch applied to the action term.

@configclass
class StockIKActionsCfg:
    arm_action = DifferentialInverseKinematicsActionCfg(
        asset_name="robot",
        joint_names=[
            "shoulder_pan_joint",
            "shoulder_lift_joint",
            "elbow_joint",
            "wrist_1_joint",
            "wrist_2_joint",
            "wrist_3_joint",
        ],
        body_name="wrist_3_link",
        controller=DifferentialIKControllerCfg(
            command_type="pose",
            use_relative_mode=True,
            ik_method="dls",
        ),
        scale=1.0,
        body_offset=DifferentialInverseKinematicsActionCfg.OffsetCfg(
            pos=(0.0, 0.0, 0.0),
            rot=(1.0, 0.0, 0.0, 0.0),
        ),
    )
    
    
    [Isaac Lab 3.0 Beta]

[Amos25103]

the actuator actuator dynamics, has to be fine-tuned in Isaac Lab as well,