| P1 — Concept model | Layout, dimensions, first motion | Placeholder: wheel size, motor idea, connector candidates | Fit check, free-roll, first motion | Functional mock-up |
| P2 — Drive integration | Motors, gearing, power routing | Motor mount rev.A, gearing ratio v1, power bus rev.A | Bench run, thermal spot-checks | Partial drive module |
| P3 — Control layer | Joystick, braking logic, sensors | Throttle → controllers, brake cut-off, Hall sensor wiring | Response curves, brake test, sensor sanity | Semi-functional control |
| P4 — Field prototype | Real-terrain testing, data logging | Cable protection, quick-swap connectors, IP checks | Gravel/sand/hill trials, data logs | Test-ready unit |
| P5 — Refinement | Durability & user comfort tuning | Strain relief rev.B, connector standardisation | Endurance + user feedback loops | Near-production concept |