Onshape on Mulham Fetna

From an Onshape assembly to a MuJoCo model with onshape-to-robot

contact@mulhamfetna.com (Mulham Fetna) — Wed, 16 Sep 2026 00:00:00 +0000

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
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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
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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.

From an Onshape assembly to a robot ROS 2 can reason about

contact@mulhamfetna.com (Mulham Fetna) — Tue, 08 Sep 2026 00:00:00 +0000

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
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Each of these exists because its absence cost real time on this project.

Code-to-CAD: Generating a 15×15 Microneedle Array Four Ways

contact@mulhamfetna.com (Mulham Fetna) — Mon, 07 Sep 2026 00:00:00 +0000

The same 15×15 microneedle array, generated four ways in code. The interesting part isn’t the loops — it’s that three of the four scripts refuse to merge the 225 cones into the baseplate at all, and hand that job to the slicer instead.

Onshape on Mulham Fetna

From an Onshape assembly to a MuJoCo model with onshape-to-robot

The design #

The design has a history #

Start

2026-09-02

v1.0.0 — MediaPipe

2026-09-06

v1.0.1 → Main

2026-09-08

V3 → Mujoco branch

2026-09-16

From an Onshape assembly to a robot ROS 2 can reason about

Five rules that move work back into CAD #

Code-to-CAD: Generating a 15×15 Microneedle Array Four Ways

The design
#

The design has a history
#

Five rules that move work back into CAD
#