Opus 5.5 builds an interactive 5:1 planetary gearbox from one prompt
Given only the prompt "create me an interesting CAD 3D of any object," Opus 5.5 chose a planetary gearbox whose gears mesh correctly and whose output spins at exactly one fifth of the input speed, with orbit, explode, x-ray and live speed controls.
1 prompt, 3 planet gears and a 5:1 gear ratio that actually works, all from Claude Opus 5.5. I typed "create me an interesting CAD 3D of any object" and gave it nothing else to go on. It picked a planetary gearbox on its own, the same mechanism you find inside electric screwdrivers, e-bikes and robot joints. The gears really mesh as they turn, and the output spins at exactly one fifth of the input speed because the math behind it is correct. You can orbit it, explode it apart, x-ray a single part and change the speed live.