Cerberus V1: Jetson Case v8 — 8 Iterations with VLM Design Review

The design problem

The Jetson Orin Nano Super Developer Kit needs a protective case that mounts inside Cerberus V1's chassis. It has to be 3D-printable on a standard bed, provide access to all ports, route camera cables, and slide securely into the chassis frame.

The approach

Eight iterations of an OpenSCAD parametric design, with each revision sent to a vision-language model for review. The VLM checked for: - Dimensional consistency (do the port cutouts match the board layout?) - Printability (are there overhangs that would need supports?) - Assembly fit (will the sliding rails actually work?) - Cable routing conflicts

Each iteration addressed specific feedback before the next render.

What shipped

Final design (v8): - 4-wall open-top tray — wires route over the top, no GPIO passthrough needed - Sliding rails (1.5mm × 2mm, sides only, flush with bottom) — snaps into chassis channels, no screws - 4 individual USB-A cutouts in a 2×2 grid — each port has its own opening, no shared slots - Individual cutouts for DC barrel jack, DisplayPort, USB-C, and Ethernet - 2 MIPI CSI ribbon cable slits on the front face — one for each camera connector - Power button hole on the back panel - MicroSD slot on the left side

Print specs: PLA, 0.4mm nozzle, 0.2mm layers. No supports needed — the tray prints face-up.

What we learned

Three lessons from the design loop that apply to any CAD + VLM workflow:

1. OpenSCAD caching is aggressive. The render cache reuses computed geometry even when parameters change silently. A full purge (rm -rf ~/.local/share/OpenSCAD) is sometimes needed between iterations to get an honest render.

2. VLMs are good at dimensional consistency checks. "Does the USB-C cutout actually align with where the USB-C port is on this board?" is a question the model handles well from a render. "Will this print without supports?" is harder — the model sometimes misses overhangs that are obvious to a human with print experience.

3. Iterations compound. Each round of "fix this one thing" produced a render that showed the next issue more clearly. The final v8 design looks obvious in hindsight, but it took all seven iterations of incremental fixes to get there.

The OpenSCAD source is at vehicles/cerberus/V1/jetson_case.scad. The full iteration pattern is documented in knowledge/playbooks/3d-cad-design.md.