Hardcore MCP Practice: AI Designs Manufacturable Machines via Real CAD Engine
SpeedyBrowser45 · reddit · 2026-08-11
A developer showcased MechFaber, an AI agent project capable of designing machines with real physical constraints, rather than just pretty renders. The author initially tried letting LLMs do CAD directly, but because models lack a 'ground truth' for physical geometry, they produced plausible-looking but structurally impossible nonsense.
Changing the approach, the author made the model handle decision-making while an underlying engine handles constraints, building an MCP-based system:
- Real Geometry & Parts: The engine uses a B-rep kernel and an actuator library with real specs. When the model needs a number, it queries the kernel instead of guessing.
- Mandatory Validation Gates: Every build is checked for interference, joint travel, and fastening. Fails are rejected and handed back to the model.
- Physics & Firmware Simulation: Physics tests run in MuJoCo, while firmware runs real C code on an emulated ARM MCU via Renode.
Currently, the system outputs exact CAD assemblies, wiring looms, BOMs, and firmware. The next step is hardware-in-the-loop co-simulation to test gait controller PD gains before cutting metal.
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