STEP to URDF Converter — CAD to robot model online, with computed inertia

Free online STEP to URDF converter: tessellates CAD geometry in your browser (OpenCascade WASM), exports STL meshes, and computes mass, center of mass, and the full inertia tensor from the actual geometry. Nothing is uploaded.

Drop a .step / .stp file (single part or assembly — each solid becomes a mesh):

Material density: kg/m³ (2700 = aluminium, 7850 = steel, 1240 = PLA)
STEP file is in millimetres (converted to metres — URDF requires SI)

What gets computed (not guessed)

Property	Typical manual workflow	This tool
Mass	Weighed or guessed	Integrated from mesh volume × density
Center of mass	Often left at origin (wrong)	Integrated from geometry (divergence theorem)
Inertia tensor	Copy-pasted from another robot	Full 6-component tensor about the COM, from the actual triangles
Units	mm/m mix-ups (the classic 1000× sim explosion)	Explicit mm→m conversion, on by default
Meshes	Manual CAD export per part	Binary STL per solid, visual+collision wired up

Scope (honest): this free tool produces one URDF link per solid, welded with fixed joints — correct for a rigid part or a base assembly. Defining articulated joints between solids (axes, limits, tree structure) needs engineering input; the guided multi-link wizard with joint definition is a Pro feature. Validate output with the URDF validator or convert it for MuJoCo with the MJCF converter.