When it is running, a miniature yellow and black buoy hangs from eight motor-driven lines above a white platform and rides real ocean conditions, bobbing roughly 40 mm and tilting about 22 degrees. The maker treats the hull as a pure wave follower: heave tracks the surface height and tilt tracks the slope, all driven by live marine data arriving over Wi-Fi.
Underneath, an ESP32-S3 with 8 MB of PSRAM drives eight steppers through TMC2209 drivers on UART, each motor turning a green spool past guide pulleys. The lines run in a crossed layout, which the maker says keeps the buoy rigid once line lengths are fixed, removing any need for feedback. A rotary encoder handles control, an ST7789 screen shows wave statistics and setup prompts, and a mobile web app displays a North Sea station map for switching between stations.
Two details stand out. The sea model builds a JONSWAP spectrum from wave height, peak period and direction, splits it into components with random phases and directional spread, and sums them live inside a 100 Hz loop on the second core. And homing is elegantly simple: each line winds in at low fixed current until its motor slips, leaving all eight equally tight, with that point set as zero. Setup itself is guided, with the buoy seated in a removable black conical stand and lifted clear by the motors before the stand comes off.
The trade-off is that nothing is measured: no load cells, no encoders, no current sensing. Tension figures came from an offline static force-balance script, with motion limits kept inside the envelope it checked, and each line stays between about 0.8 and 6 N. Whether that open-loop approach stays trustworthy over long unattended runs seems the main open question, though a night rest mode that holds the lines tight until the button is pressed at least reduces the hours of active cycling.