Microduck replica reconstructs hardware from simulator files

Pollen Robotics publishes the code, MuJoCo simulator, and reinforcement-learning stack for its Microduck under Apache 2.0. The company keeps the mechanical drawings, PCB schematics, and bill of materials private, leaving developers without an official manufacturing package.

Software engineer fanhao reconstructed the missing assembly information from the published simulator, meshes, and firmware. The resulting replica repository contains transformed 3D models, assembly drawings, inferred hardware specifications, and a reconstruction of the custom electronics.

Meshes become an assembly

The reconstruction starts with Microduck’s MJCF file, MuJoCo’s XML format for describing simulated bodies. A physically accurate model must encode the robot’s kinematic tree, including part relationships, relative positions, joint axes, travel limits, masses, and inertia tensors. Combined with the 47 published STL meshes, those records provide much of the information normally found in a CAD assembly.

1. Parse the MJCF body tree and joint definitions.
2. Resolve each mesh from its local coordinates into world coordinates.
3. Group meshes by rigid body and export the assembled geometry.
4. Inspect holes and other mesh features to infer fasteners and bearings.
5. Read firmware interfaces to identify sensors, controllers, and PCB connections.

Applying the world transforms solves a practical import problem. The upstream STL files use local coordinate frames, so loading them directly into FreeCAD or SolidWorks places many parts at the origin. The repository provides seven assembly drawings, a full