The simulated hand was never modelled by hand. It is an Onshape assembly — five SG90 servos, fifteen knuckle mates, a palm full of tendon channels — pulled through the Onshape API and written out as MuJoCo XML. Here is the design, and every setting that steers the export. Open the Onshape assembly The design # Your browser cannot play this video. Download video.
Palm and fingers: four three-phalanx fingers and a three-segment thumb, every knuckle a revolute mate with limits. The RGB triads in the views are mate connectors. Tendon channels: one per finger, running down the palm into the base. Servo block: five SG90-class servos, staggered so each horn sits under a tendon exit. The design has a history # Start 2026-09-02 The first version in the history. v1.0.0 — MediaPipe 2026-09-06 The joint-angle-driven hand behind the RViz predecessor project. v1.0.1 → Main 2026-09-08 Point release and the main line the later work branches from. V3 → Mujoco branch 2026-09-16 The current design used by this twin — the version with the servo base block shown above. Onshape version history Mate features 43 part instances, 112 mate features: the 15 dof_* knuckle mates, the servo mates, and many Fastened mates.
Bridging a modern parametric CAD platform and a fifteen-year-old XML standard is where most roboticists lose days. The exporter translates exactly what it sees — so every shortcut taken in CAD becomes a bug in ROS. → Open the assembly on Onshape — it is public, so everything below is checkable against the source.
The assembly: four fingers on blue linkages, the thumb on an orange one, all mounted to a single palm block. onshape-to-robot is a compiler. Assembly in, robot description out. It reads mate names, mate limits and material densities directly from the CAD document and writes them into URDF as joint names, joint limits and inertia tensors.
That is a genuinely good deal — done properly, the physical properties of your robot are generated rather than hand-typed, and they stay correct when the mechanism changes. Done improperly, you spend your evenings editing XML by hand and discovering that your ring finger has no knuckle.
flowchart LR A["Onshape assembly
mates · limits · materials"] --> B["onshape-to-robot
API pull"] B --> C["robot.urdf
links · joints · inertials"] B --> D["assets/*.stl
visual + collision meshes"] C --> E["robot_state_publisher"] C --> F["JOINT_MAPPING
limits transcribed by hand"] D --> G["RViz / Gazebo"] Five rules that move work back into CAD # Each of these exists because its absence cost real time on this project.
