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Flexiv Robotics Rizon4 Description (MJCF)

Important

Requires MuJoCo 3.1.3 or later.

Changelog

See CHANGELOG.md for a full history of changes.

Overview

This package contains a MuJoCo robot description (MJCF) of Rizon4 developed by Flexiv Robotics.

URDF → MJCF derivation steps

  1. Loaded the URDF into MuJoCo and saved a corresponding MJCF.

  2. Manually edited the MJCF to extract common properties into the <default> section.

  3. Added position-controlled actuators for the arm with three default classes (joint1, joint2, joint3) matching the three motor sizes and their respective actuatorfrcrange limits (123, 64, and 39 Nm).

  4. Rounded material properties (specular, shininess, rgba) to 2 significant digits.

  5. Computed per-joint PD gains (kp, kv) from the diagonal of the joint-space mass matrix at the home configuration. The gains follow a second-order response model:

    • kp = M_ii * w_n^2
    • kv = 2 * zeta * M_ii * w_n

    Natural frequencies are chosen per actuator class so that each actuator saturates at approximately 10 degrees of position error (1.5 Hz for joint1, 2.0 Hz for joint2, 6.0 Hz for joint3), with a critically damped response (zeta = 1). See compute_gains.py to reproduce or adjust these values.

  6. Added a home keyframe.

  7. Added scene.xml which includes the robot, with a textured groundplane, skybox, and haze.

License

This model is released under an Apache-2.0 License.