A monowheel is a one-wheeled single-track vehicle similar to a unicycle. However, instead of sitting above the wheel, the rider sits either within it or next to it. The wheel is a ring, usually driven by smaller wheels pressing against its inner rim. Most are single-passenger vehicles, though multi-passenger models have been built. Hand-cranked and pedal-powered monowheels were built in the late 19th century; most built in the 20th century have been motorized.

Some modern builders refer to these vehicles as monocycles, though that term is also sometimes used to describe motorized unicycles. Today, monowheels are generally built and used for fun and entertainment purposes, though from the 1860s through to the 1930s, they were proposed for use as serious transportation.

In a two-wheel mode of transportation, two systems (wheels) affect motion. Typically one wheel provides the force to control speed, while the other handles changes in direction (steering). For a monowheel, both direction and speed are controlled through the same physical apparatus; this generally makes steering more difficult. In a majority of systems, change in direction is affected by the rider shifting his or her weight, or in the sudden movement creating a shearing force between a handhold and the axis that the driver is settled on. Better control can usually be achieved at slower speeds. Because of the steering problem, monowheels never caught on as a widely accepted mode of transportation.

There numerous drawback to monowheels such as Limited horizontal stability (a single wheel can fall over, unless it is quite wide or has some form of active stabilization, such as a gyroscope). Some designs have used outrigger skids or small wheels to address this. In many one-person designs, being at a stop requires the driver to put their feet on the ground, the same way as on a motorcycle. There is also a risk of ‘gerbiling’: In most designs, if the driver accelerates or brakes too hard, it is possible that the force applied overcomes the force of gravity keeping the rider at the bottom of the wheel, sending the rider spinning around the inside of the wheel. This is known as gerbiling because it has some similarity to the situation of a gerbil running too quickly inside of a hamster wheel.

There have been many proposals for variants or uses, such as a horse-drawn monowheel or a monowheel tank. A variant was proposed that placed two riders outside of the wheel itself, with one person on each side to provide for balance. An electric monowheel called Dynasphere was tested in 1932 in the United Kingdom. One interesting variant called a RIOT wheel was presented at Burning Man in 2003. It involves the passengers sitting in front of the wheel and being balanced by a heavy counterweight inside the wheel. Rather than the typical ring drive, this vehicle is powered through a sprocket attached to the spokes. A company in the Netherlands began taking custom orders of a monocycle configured variant called the Wheelsurf in 2007.

In 1971, an American inventor named Kerry McLean built his first monocycle (aka monowheel). In 2000, he built a larger version, the McLean Rocket Roadster powered by a Buick V-8 engine, which subsequently crashed in 2001 during the initial test run. Fortunately, McLean survived and proceeded to build over 25 different variations of his version of the monocycle, from pedal powered models, 5HP models, all the way up to V8 powered models.


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