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Support MJCF muscle actuators - #3752

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han-xudong:feat/mjcf-muscle-actuator
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Support MJCF muscle actuators#3752
han-xudong wants to merge 1 commit into
newton-physics:mainfrom
han-xudong:feat/mjcf-muscle-actuator

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@han-xudong

@han-xudong han-xudong commented Jul 31, 2026

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Description

Import MJCF muscle actuator shortcuts, including inherited muscle dynamics and force-law parameters. The change preserves explicitly authored actuator lengthrange, expands the shortcut into dynprm, gainprm, and biasprm, and reconstructs it with MjsActuator.set_to_muscle() without introducing a separate Newton-native muscle model.

Closes #3751

Checklist

  • New or existing tests cover these changes
  • The documentation is up to date with these changes
  • CHANGELOG.md has been updated (if user-facing change)

Test plan

uv run --extra dev python -m unittest newton.tests.test_mujoco_general_actuators.TestMuJoCoMuscleActuators -v
uvx pre-commit run -a

All three focused tests pass on CPU. CUDA is unavailable locally. Tests compare authored and default parameter arrays plus activation, force, and joint motion over five MuJoCo steps.

New feature / API change

import newton

mjcf = """
<mujoco>
  <worldbody><body><joint name="slide" type="slide"/><geom type="sphere" size="0.1" mass="1"/></body></worldbody>
  <actuator><muscle joint="slide" lengthrange="0.5 1.5" force="5"/></actuator>
</mujoco>
"""
builder = newton.ModelBuilder()
builder.add_mjcf(mjcf, ctrl_direct=True)

@han-xudong
Support MJCF muscle actuators
cf3292f 
Expand muscle shortcuts into native activation, gain, and bias parameters, preserve authored length ranges, and reconstruct them with MuJoCo's shortcut API. Compare defaults and dynamic behavior with native MuJoCo.
@han-xudong
han-xudong requested a deployment to external-pr-approval July 31, 2026 07:23 — with GitHub Actions Waiting
@han-xudong
han-xudong requested a deployment to external-pr-approval July 31, 2026 07:23 — with GitHub Actions Waiting
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Reviewing files that changed from the base of the PR and between 0f97d2a and cf3292f.

📒 Files selected for processing (4)
  • CHANGELOG.md
  • newton/_src/solvers/mujoco/solver_mujoco.py
  • newton/_src/utils/import_mjcf.py
  • newton/tests/test_mujoco_general_actuators.py

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[FEATURE] Support MJCF muscle actuators

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@han-xudong