Dynasphere (vehicle)

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The Dynasphere is a monowheel vehicle designed by John Archibald Purves and patented in 1930. Purves was inspired by a sketch from Leonardo da Vinci. Two prototypes were built: a small electric model and a gasoline-powered one. The gasoline engine was a two‑cylinder air‑cooled Douglas unit with a three‑speed gearbox and reverse, offering either 2.5 or 6 horsepower depending on the source.

The Dynasphere could reach about 25–30 mph (40–48 km/h). The gasoline prototype stood about 10 feet (3.0 m) tall, made of iron lattice, and weighed around 1,000 pounds (450 kg). The next version used ten outer hoops with a leather lining to keep a low ground profile. The driver’s seat and motor were built as one unit and mounted inside the outer hoop’s inner rails.

As it moved, the inner unit would try to “climb” the spherical rails, causing the lattice cage to roll forward. Steering started out crude, with the driver leaning in the direction of travel to steer. Purves envisioned future models with gears to shift the inner housing and tip the vehicle without leaning. The ten-hoop model added a steering wheel connected to tipping gears.

The ten-hoop Dynasphere was shown in a 1932 Pathé newsreel at Brooklands, where its advantages were described and demonstrated. Beatrice Shilling and Purves’ son tested the vehicle on roads, including an attempt to topple it over. A smaller novelty version, the Dynasphere 8, was built to seat eight passengers for beach use.

Purves was optimistic about the idea. A 1932 Popular Science article quoted him after a beach test drive, saying the Dynasphere reduced locomotion to a simple form, offering power economy and the potential of a high‑speed future vehicle. A 1935 Meccano Magazine piece noted it was still experimental but “possesses so many advantages” that large wheel systems could eventually become common on highways.

According to later sources, the Dynasphere never succeeded because, while it could move, it was very hard to steer or brake. Another issue was “gerbiling”—the inner housing tending to spin inside the moving frame during acceleration or braking.