MuJoCo Actuator Targets#

Code

MUJOCO.DJ.002

Validator

MuJoCoActuatorTargetsChecker

Compatibility

other

Tags

🔑

Summary#

MuJoCo actuator prims must target valid MuJoCo-driven USD physics joints and author valid actuator parameter values.

Description#

MuJoCo-driven articulation control is represented by MjcActuator prims. Every MjcActuator prim must:

  • target exactly one joint with mjc:target

  • target a valid non-fixed UsdPhysics.Joint

  • target a joint that applies MjcJointAPI

  • author paired range attributes when ranges are present

  • keep mjc:ctrlRange:min, mjc:ctrlRange:max, mjc:forceRange:min, and mjc:forceRange:max finite, with min less than or equal to max

  • keep authored mjc:gainPrm and mjc:biasPrm values as non-empty numeric arrays

  • author a non-empty mjc:biasType value when mjc:biasType is present

Every non-fixed MuJoCo joint in the feature contract must be targeted by at least one MjcActuator.

Why is it required?#

  • Ensures MuJoCo actuators resolve to concrete USD joints.

  • Prevents orphaned actuators and unactuated MuJoCo-driven joints.

  • Catches invalid control, force, gain, and bias values before MuJoCo import.

Examples#

# Valid: actuator targets a MuJoCo-marked USD joint.
def MjcActuator "shoulder_actuator"
{
    rel mjc:target = </robot/Physics/shoulder>
    float mjc:ctrlRange:min = -3.14
    float mjc:ctrlRange:max = 3.14
    float mjc:forceRange:min = -150.0
    float mjc:forceRange:max = 150.0
    float[] mjc:gainPrm = [100.0, 0.0, 0.0]
    float[] mjc:biasPrm = [0.0, -100.0, -10.0]
    token mjc:biasType = "affine"
}

# Invalid: actuator target is missing.
def MjcActuator "bad_actuator"
{
    float mjc:ctrlRange:min = -1.0
    float mjc:ctrlRange:max = 1.0
}

How to comply#

  • Author one or more MjcActuator prims for MuJoCo-driven articulation joints.

  • Set rel mjc:target to exactly one valid non-fixed UsdPhysics.Joint that applies MjcJointAPI.

  • Keep authored control and force ranges finite and ordered.

  • Keep authored gain and bias parameters numeric.

  • Do not leave MuJoCo-driven joints without an actuator target.

For More Information#

  • MuJoCo USD converter output and actuator authoring conventions.