# Remaining simulation limitations

All generated USD assets are checked against their source descriptions for geometry and physics structure, body poses, mass properties, joint axes and limits. These checks do not establish dynamic equivalence in a simulator.

## Closed-loop H2 constraints

The native [H2 MJCF](sources/unitree_ros/robots/h2_description/H2_loop.xml) defines six `equality/connect` closure constraints: left/right ankle, knee and waist connections. The URDF-to-USD conversion preserves the URDF tree but does not translate these MJCF closure constraints into the generated [H2_loop USD](generated/h2_description/H2_loop/H2_loop.usdc). It therefore must not be treated as a dynamically equivalent closed-loop mechanism. Use the included native MJCF for that representation until closure constraints are implemented and tested for the target USD simulator.

Other source mechanisms, including R1 ankle linkages, also need a simulator-specific constraint audit. A model name or the presence of linkage geometry does not establish loop closure.

## Mimic joints and hand coupling

The converter writes Newton mimic coefficients and joint references where supported. The validation script checks that authored mimic relationship targets resolve. It does not author or test PhysX mimic-joint schemas. In particular, the new standalone BrainCo hands retain their Newton mimic metadata, while their PhysX coupling remains unverified. Configurations with locked joints can also retain source mimic declarations whose behavior depends on the simulator.

## Runtime checks still required

Isaac Sim / PhysX and Newton simulation has not been run. Remaining checks include actuator commands, coupled-joint motion, closed-loop stability, contacts, gravity settling, sensors and controllers. Source transmissions and motor settings do not automatically become a tested runtime controller. Visual inspection in a renderer is also outstanding.

## Source and material warnings

The hand-equipped H1 torso Collada file contains an unsupported line primitive, and some H2 source material references are undefined. Triangle mesh geometry remains available. Original Unitree USD packages can depend on Isaac Sim's built-in `OmniPBR.mdl` shader. Per-model conversion warnings are preserved in [manifest.json](manifest.json).

## Center-of-mass correction

Generated stages explicitly author the source center of mass for every link with source inertial data, including zero offsets. This corrects the initial converter behavior where an omitted URDF inertial origin could leave USD's center of mass unspecified and allow collider-based inference. Source files remain unchanged.