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.
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 its 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 have never caught on as a widely accepted mode of transportation.
A change in direction can be effected in several ways including:
- Leaning. The most common steering solution is that the rider must lean towards his intended direction of travel to turn, and then centralize his weight again once the turn is complete.
- Turning a gyroscope to provide turning force.
- Outboard skids to provide friction drag on one side.
- At speeds faster than a walk, lightly dragging a foot on the ground will cause the wheel to lean to the opposite side. Drag the other foot to bring it back upright.
- Small wheels used for steering, either one to each side or a single unit either in front of or behind the vehicle. It is a matter of debate as to whether such a vehicle would still properly be called a monowheel.
- Steerable propellers, which could provide both steering and power to move the vehicle. It has been noted that having a propeller operating near pedestrians would likely be quite unsafe.
- Steerable tail surfaces, similar to those on airplanes. This solution would not work at low speeds.
- 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.
- Limited capacity. Monowheels tend to be larger than a car of similar carrying capacity. Most have been kept small by being built to carry only one rider and with little or no space for baggage.
- 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.
- Visibility issues. In driver-inside designs, the rider is always facing the inner rim of the wheel, which can obstruct the view of oncoming hazards.
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.
A related vehicle is the diwheel or the dicycle, in which the rider is suspended between or inside of a pair of large wheels placed side by side. An example of this would be the character Axel from the Twisted Metal series of video games published by Sony.
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.
In 2010, Nokia utilized two of McLean's monocycles in their commercials promoting the new Nokia SatNav smartphone.
McLean's latest creation, the 2011 McLean V8 Drag Wheel, of which the wheel itself was machined out of a single piece of high-strength aircraft grade aluminum billet, was completed in 2011.
Appearances in media
- Iain M. Banks' novel Against a Dark Background contains a rare instance of a monowheel as an important feature of a fictional work.
- Stanislav Lem's novel Eden features motorized variants of the monowheel.
- Robert A. Heinlein's novel The Cat Who Walks Through Walls features a gyroscope stabilized lunar "doughnut" craft with a driver on one side and a turret gunner on the other, that can bounce over lunar obstacles.
- Amazing Three, known in Japan as Wonder 3 (ワンダー3, Wandā Surī?) or W3, features three agents from outer space who travel in a tire-shaped vehicle called the Big Wheel, which can travel at enormous speeds on both land and water (and, with modifications, through the air).
- In South Park episode "The Entity" Mr Garrison makes a gyroscope-stabilized, turbine-engine-propelled device resembling the monowheel, called "IT" (pronounced like the word "it", a play on early hype for the Segway), with a rather uncomfortable user interface.
- In the French animated television series Code Lyoko, the character Ulrich Stern uses a "monocycle" (basically a motorized unicycle) as his vehicle of choice on Lyoko. Ulrich's "Overbike" is capable of flight and land travel.
- In Star Wars Episode III: Revenge of the Sith, General Grievous uses a monowheel.
- In the animated series Star Wars: Droids the young miner Jann Tosh owns a similar wheel bike.
- In the animated series and action figure line Spiral Zone, Colonel Dirk Courage rode the Rimfire, a large monowheel with an attached cannon.
- The Mowercycle of Chaotic is a monowheel with gripping teeth that also act as sawteeth.
- The War Wheel is a huge, armored battle tank that first appeared in DC's Blackhawk comic. War wheels were also used in the Justice League (TV series). 
- In Kirby Super Star, the helper from the wheelie powerup is a monowheel.
- A futuristic version of the monowheel is shown in a few episodes of Teenage Mutant Ninja Turtles: Fast Forward.
- The fourth edition of the roleplaying game Shadowrun features a monowheel called the Horizon-Doble Revolution.
- In the videogame Wild Arms 5 the main character Dean obtains a monowheel for faster transportation around world map areas.
- In the OVA series Dirty Pair Flash Mission 3, a young female assassin called Monica drives a Red Futuristic Monowheel.
- In Hiroya Oku's manga series Gantz, the players are provided with a very fast motorized monowheel (called the Gantz Bike) to evade their alien opponents during a mission later in the story.
- In the first episode of Nadia: The Secret of Blue Water, a protagonist uses one in a rescue of the eponymous character.
- In Katsuhiro Otomo's film Steamboy (2004), Ray Steam, the protagonist of the story, uses a steam-powered monowheel early in the movie.
- In the animated adaptation of Venus Wars, one-wheeled motorcycles are used both in bloodsport and combat.
- Mobile Suit Victory Gundam features the Einrad, a colossal monowheel used as a transport vehicle for the Zanscare Empire's mobile suits.
- In Yu-Gi-Oh! 5D's, the character Jack Atlus uses a monowheel D-Wheel named "Wheel of Fortune" in riding duels.
- In Hot Wheels Battle Force 5, The Red Sentient Kytren uses The Vyirex which is a gyroscope monowheel (hence the name).
- In an episode of the British television show Scrapheap Challenge, two teams competed to build and race monowheels.
- In the Australian Reality TV show Push the Limit a monowheel challenge ended when contestant Kate Siopis fractured her wrist.
- Many monowheels were used in the closing ceremony of the 2008 Beijing Olympics.
- In a 2007 television commercial produced for the drink brand Capri Sun, a boy and a girl are both riding in variants which appear to be manufactured vehicles made of metal and fiberglass (up to the point where they are levitated into the air by a CGI effect).
- In 2010, Nokia utilized two McLean Monocycles in their commercials promoting the new Nokia SatNav smartphone. Multiple versions of the commercial were created and aired throughout the world.
- Media related to Monowheels at Wikimedia Commons
- The Museum of Retro Technology - The strange story of vehicles with insufficient wheels
- Channel 4's Scrapheap Challenge page on the Monowheel
- Monovelo, the 2008 Beijing Olympic Games Monowheel
- Wheelsurf, the Dutch/Brazilian motorized Monowheel
- McLean Rocket Roadster Monocycle - U.S. street-legal Buick 215 V8-powered monocycle built by Kerry McLean.
- Ben Wilson's simplified, DIY monowheel
- The RIOT Wheel is a huge, heavy motorized single-wheel vehicle, originally built for Burning Man, the natural home of deviant vehicles
- Monowheels the Weirdest Technology Known to Man
- Speedy New Motor-Hoop Amazes Italians, Popular Science, December 1924, page 40, Scanned by Google Books: http://books.google.com/books?id=FSkDAAAAMBAJ&pg=PA40
- Amazing New Motor-Driven Hoop May Be Car of the Future, Popular Science, May 1932, front cover and page 63, Scanned by Google Books: http://books.google.com/books?id=1ScDAAAAMBAJ&printsec=frontcover
- War Tank on One Wheel, Operated by One Man, Popular Science, November 1933, front cover and page 47, Scanned by Google Books: http://books.google.com/books?id=7CcDAAAAMBAJ&printsec=frontcover
- Cycle World: Circle Cycle
- Imapct Lab: History of the World’s Craziest Invention - The Monowheel
- Home & Garden Publications: Vehicles with Insufficient Wheels
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