Beach Cart Conversion
You already own a beach cart or wagon. You want it to drive itself across the sand instead of dragging your shoulder out of its socket. This page is the honest version of how that conversion works — from the builder of the AUTO-CART, the fully autonomous beach cart 1.5 million people watched follow its owner down the beach.
The part that kills most conversions
It isn't the motor. It's the wheels. Soft balloon tires grip sand far better than they grip a smooth plastic hub — so the first time real motor torque hits, the hub spins inside the tire. On most balloon tires the valve stem routes through the hub, which means one good slip shears the stem clean off and the tire is dead on the beach. It's the most common field failure on kit-built and home-converted carts, and almost nobody warns you about it.
Two things prevent it. First, a hub that locks the tire mechanically, not just by friction. Second, the right adhesive bond as insurance. (A side note worth knowing: on Wheeleez tires the valve stem exits outside the hub — so even if slip happens, nothing tears. That detail is a real part of what their premium price buys.)
The locking hubs
The KMJ Dynamics two-piece castellated hub is the wheel part of the conversion solved: printed in carbon-fiber nylon, it clamps the tire between interlocking halves so motor torque can't rotate the hub independently, with the same urethane adhesive spec the real AUTO-CART runs on its dual 3 kW drivetrain. Today's files fit 16.5-inch Wheeleez-class balloon tires; additional fitments — including 12-inch Wheeleez — are in development and get added to the pack as free updates.
The Print Files Pack — $24. All 31 printed parts including the locking hubs, with print settings, material rules, and the mounting + adhesive spec. Buy once, every future fitment and revision included.
The rest of the conversion
Hubs keep the wheels alive; the drivetrain makes them turn. Motor sizing for sand (hint: one small hub motor will disappoint you), battery chemistry and a real BMS, controller wiring, throttle or RC control — that's the other 80% of a conversion, and it's exactly what the frame, drivetrain, and power chapters of the Complete Build Package cover, with real part numbers and real prices. The manual is color-coded: follow the green chapters for a remote-control conversion and skip the autonomy stack entirely (or add it later — the follow-me brain is a separate layer).
Honest expectations
A conversion done right — locked hubs, adequate motors, LiFePO4 power — turns a dead-weight wagon into a machine that hauls 400 lb across soft sand while you walk. Done wrong, it eats tires and strands you at the far end of the beach. The difference is about $24 of hub files and reading the drivetrain chapter before buying a motor kit. Questions before you start? hello@kmjdynamics.com — I read everything.