Python: per-step MJCF actuator control + multibody state readback#12
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Python: per-step MJCF actuator control + multibody state readback#12haixuanTao wants to merge 1 commit into
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- GpuMultibodySet::sync_joint_data_from_rapier: refresh every link's joint data (motor targets/gains, limits) from the rapier multibody set in one buffer write, mirroring from_rapier's traversal order. - NexusState::control_multibody_motors: runtime actuation entry point that mutates the rapier joints (e.g. rapier3d-mjcf's apply_controls_multibody) and pushes the refreshed joint data to the GPU, without marking the world dirty (no rebuild). - Viewer::read_multibody_links + links_workspace COPY_SRC: one-readback joint coordinates, link world poses and world-space velocities per env. - Python: NexusState keeps the MjcfRobotHandles from insert_mjcf and exposes actuator_names() / apply_actuator_controls(viewer, ctrl, env) with full MJCF actuator semantics; NexusViewer.read_multibody_links(state, env) returns (coords, positions, quats, linvels, angvels) numpy arrays. Together these make MJCF robots drivable per control step from Python (position-servo PD runs inside the solver) with full state observation -- the two pieces sim-to-sim eval loops need. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Makes MJCF robots drivable per control step from Python, with full state observation — the two pieces an RL / sim-to-sim evaluation loop needs. Follow-up to #7/#8, standalone on main.
What
Control —
NexusState.apply_actuator_controls(viewer, ctrl, env=0)applies one MJCF control vector (one entry per<actuator>, in actuator order —NexusState.actuator_names()reports the order) with full MJCF actuator semantics viarapier3d-mjcf'sapply_controls_multibody(<position>servos with kp/kv,<motor>force/gear, force limits), then pushes the refreshed joint-motor state to the GPU in one buffer write. The PD servo itself runs inside the GPU solver, so there is no per-step solver round-trip beyond that single upload.Observation —
NexusViewer.read_multibody_links(state, env=0)reads every link's state back in one readback:(coords, positions, quats, linvels, angvels)numpy arrays (one row per link, GPU traversal order).coordsare the generalized joint coordinates (a revolute joint's angle iscoords[3], the first angular slot); poses/velocities are world-space.How
GpuMultibodySet::sync_joint_data_from_rapierrefreshes each link'sGenericJointdata (motors, limits) from the rapier multibody set, mirroringfrom_rapier's traversal order, then uploadslinks_staticonce. Only joint data is touched — coordinates/velocities/mass properties are untouched, so this can't teleport links.NexusState::control_multibody_motorswraps "mutate rapier joints, then sync" without marking the world dirty (motor updates are control, not topology — no GPU rebuild).links_workspacegainsCOPY_SRC+ public accessors for the readback.NexusStatekeeps theMjcfRobotHandlesfrominsert_mjcf.Validation
On the LeRobot bipedal platform MJCF (12 position actuators, 13 links): a passive run collapses to torso z ≈ −0.34 within 1 s; driving the servos each step holds it at z ≈ −0.02, and
read_multibody_linkstracks joint angles/limits throughout.cargo checkclean onnexus3d,nexus_viewer3d,nexus_python3d.🤖 Generated with Claude Code