One-Wheeled Wonder

Barring the odd three-wheeler tricycle, most wheeled vehicles throughout history have sported an even number of wheels, usually four for bigger vehicles like carriages and cars. Bikes and motorbikes have two. But that doesn't seem streamlined enough for some futuristic aesthetics. This trope describes creatures (usually robots or cyborgs) or vehicles that move by balancing on a single wheel, or occasionally a spherical ball.

Try not to think too hard about how it stays upright.

Truth in Television insofar as the unicycle has been in use since at least the late 19th century, when riders of penny-farthings found that they could lean forward, raising the much smaller rear wheel off the ground, and still maintain balance. Eventually the rear wheel was left off of the design altogether, resulting in the modern unicycle. However, it has largely been regarded as a gimmick since the development of the safety bicycle, a significantly more practical and safer pedal-powered vehicle.

Monowheel Mayhem is a subtrope in which a vehicle is a single wheel, with the rider and components sitting inside it. Non-robotic creatures to which this trope applies are examples of Bizarre Alien Locomotion.

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Examples:

Anime & Manga

• Doraemon:
  • Log from Doraemon: Nobita's Drifts in the Universe is the new Robot Buddy of the cast, who travels around with a single wheel under his feet.
  • Captain Silver's robotic guards from Doraemon: Nobita's Treasure Island are spherical robots with a single wheel under their feet for traveling around.
• Dragon Ball: Launch is shown riding a one-wheeled bike when she robs a train in her introductory episode.
• Ricardo Fellini in Gundam Build Fighters occasionally uses a support unit called the Meteor Hopper, a one-wheeled motorcycle for his Wing Gundam Fenice. He eventually stops using it after upgrading his Gundam to transform.
• Venus Wars features a violent sport called Battle Biking, which is kind of like roller derby fought on one-wheeled monobikes. The heroes of the manga and anime, the Killer Commandos team, use their bikes in their first guerilla action against the Ishtar invaders.
• Yu-Gi-Oh! 5Ds: "Visor's" (actually Bruno's) Duel Runner "Delta Eagle" has a very unique shape compared to other duel runners in the series. While most look like highly customized motorcycles (aka they have two wheels), his has a single massive wheel behind the rider's seat, while the front has a curved angular shape resembling a beak. When he rides it, the whole thing balances on the back wheel. However, when it's parked, it uses two tiny wheels on the front to prevent it from falling over, kind of like a tricycle. Those don't come in contact with the ground when he drives. A flashback from Bruno's life before he came to the current era reveals that his peculiar configuration will be commonplace in the future.

Film — Animation

• The LEGO Ninjago Movie: Cole's Quake Mech has a single giant wheel instead of legs.
• The Lorax (2012): Ted's scooter has only one wheel, looking like a big ball. This doesn't stop him from doing impressive stunts with it.
• Officer Shrift from the animated adaptation of The Phantom Tollbooth gets around on a wheel that resembles that of a rolling chair, connected to something that looks like a car jack that can be raised to compensate for his height. It's unclear whether this is a vehicle that he is seated on under his long jacket or a part of him or what.
• Poet Anderson: The Dream Walker and its prequel comics features plenty of one-wheeled hoverbikes, mostly used by non-evil characters.
• Bigweld in Robots rides on one giant ball, which makes up most of his body.
• A little hard to see, but M-O from WALL•E runs around on a motorized ball.

Film — Live-Action

• Alita: Battle Angel: Hugo uses a monowheeled motorcycle to move around Iron City, and frequently gives rides to Alita.
• One of the bikes in the Mega Race during Spy Kids 3 Game Over is a motorized unicycle with a very high seat.
• Star Wars:
  • The droid waitress WA-7 in Dexter's Diner on Coruscant from Attack of the Clones serves customers while balanced upon a single wheel.
  • BB-8 from The Force Awakens is a little droid that rolls around on a ball.

Literature

• Ciaphas Cain: One of the techpriests in Emperor's Finest and Caves of Ice had his lower body replaced with a single wheel. Made even worse by the fact that techpriests have huge metal dendrites attached to their backs and like to replace as much of their body with metal as possible, though Ciaphas mentions that he must have very good gyroscopes to work.
• Piers Anthony's Cluster Series has several unusual alien physiologies. One of them is the Polarian — a race that travels and balances on a big ball — which makes it a bit easier on the creatures than the usual one-wheel design.
• The Mulefa in the third book of Phil Pullman's His Dark Materials trilogy. They're a race of Starfish Aliens who use a giant round seed as a wheel, and attach it to their two middle feet.
• Groomatron from House of Robots: Robot Revolution is drawn as using a single wheel for mobility.
• In Robert A. Heinlein's novella "If This Goes On—" the protagonist (at that point on the run from the police) at one point casually claims to have ridden "a unicycle" on a very steep mountain road. The person he tells this to clearly doesn't believe him, but from the context it's clear that the story is the equivalent to claiming to have ridden on a steep mountain road on a bicycle—it isn't the unicycle part that's unbelievable or even particularly unusual in that setting (which also includes Flying Cars).
• One of the road-gang in The Last Continent rides a huge wheel with a saddle on top, pulled by an emu.
• In Robert Heinlein's short story "The Roads Must Roll" a "tumblebug" is a vehicle "about the size and shape of a kitchen stool, gyro-stabilized on a single wheel". They're used by the engineers who maintain the moving roadways that power society to move around among the massive machinery down below the roadways.
• Heinlein really liked this one. In Stranger in a Strange Land Jill suggests to Mike that a good present for Duke would be "one of those cute little Belgian unicycles" as he could spend hours playing with the engine.
• In Wizard by John Varley the mob on Earth chasing the Titanide in the beginning is mounted on powered unicycles.

Live-Action TV

• Tokusou Sentai Dekaranger and its American counterpart Power Rangers S.P.D. has DekaBreak/Omega Ranger with a one-wheeled motorcycle as his personal vehicle.

Music

• Animusic: The drum robots in "Beyond The Walls" and all the instruments in "Pogo Sticks" stand on two wheel side by side, allowing them to lean forward and backwards.

Tabletop Games

• A citizen in the BattleTech universe can purchase the DB-6000 Defiance Bluestreak racing-style monocycle, which runs on a hydrogen fuel cell.
• The Castle Falkenstein supplement Steam Age throws in steam-powered personal unicycles. Because why not?
• In the Warhammer 40,000 Gaiden Game Gorkamorka, one of the Kustom Leg Replacements that an Ork can randomly acquire from a visit to the Doc's Serjery is the Gyro-Stabilised Monowheel. This crude prosthetic consists of a single wheel attached to an engine that replaces the Ork's legs. A model with a Monowheel increases their Movement stat but is unable to move through difficult terrain, board vehicles or climb walls.

Video Games

• Ball Breakers for the Playstation have you playing as a monowheeled robot in an arena, fighting other monowheeled robots for points. You can even upgrade your stability after battles later in the game, when enemies start getting tough so you don't slip and fall.
• Claptrap from the Borderlands series is a small robot that gets around on one single wheel. He even tilts in the correct directions when he starts moving.
• The Stillborn Franchise Defenders of Dynatron City included Buzzsaw Girl, a mutant heroine whose lower body was a buzzsaw that functioned as a wheel.
• Hard Edge have gigantic robots on a single sphere for it's feet as recurring enemies. They can balance themselves surprisingly well despite their absolutely humongous upper body.
• The Securitron robots, which form the personal guard of the post-apocalyptic mogul Mr. House in Fallout: New Vegas, stand on a single small wheel.
• The system-repair drones from FTL: Faster Than Light move around on a single wheel. Anti-personnel and boarding drones, by contrast, move on twin treads, giving them a more intimidating design.
• Maestro in Mystery Mountain. He is the only android designed this way; Mrs. Beasley and Eggbert hover and the rest are bipedal.
• The clown of Kick Man rides on a unicycle.
• The helper Wheelie from Kirby Super Star. You can ride onto it and become the Wheelie Rider.
  • Taken even further with the other Wheelies from Kirby Air Ride, with Wheelie bike, Wheelie Scooter and Rex Wheelie.
• The Type-9 Surveillance Robots Machine Hunter. It's fast and comes with a built-in rocket launcher. It's a headache if it's an enemy, until you disable it and take over it's circuits thanks to your Machine Hunter powers.
• Mega Man
  • Mono Roader in Mega Man 4.
  • Camon in Mega Man 5.
  • Mega Man 7 has Gilliam Knight and Turbo Roader.
  • Sepa Roader in Mega Man 10.
  • Rush Roader in Mega Man X.
  • Kerberos in Mega Man Zero.
  • HotRoader, and its family HotAuto and HotTero, in Mega Man Star Force.
• Mighty Goose have multiple one-wheel tanks piloted by enemy robots serving as enemies in various areas. Though the titular character can sometimes hijack a one-wheeled tank for himself to kick ass.
• Mighty No. 9's Round Digger and Round Borer have spherical bodies with a separately moving belt around its centreline that it uses as a wheel.
• The obscure video game Mo Ho had gladiatorial robots with a single ball on which they moved.
• The protagonist of Pokémon Colosseum travels around Orre in a motorcycle that has one wheel in the back, plus a sidecar with...some kind of...hover-thing. Good luck figuring out how this thing works.
• Skylanders has two: The legendary Giant Bouncer and the Swap Force entrant Magna Charge.
• The eponymous protagonist of Rocket: Robot on Wheels for the Nintendo 64.
• Ruff N Tumble have you battling robotic enemies throughout the game, the first batch being round, roly-poly robots who moves about with a single tiny wheel in place of feet.
• Some of Dr. Eggman's robots from the Sonic the Hedgehog video game series are like this. The earliest (and probably most notable) example is the Motobug from Sonic the Hedgehog.
• The Octo Samurai from Splatoon 2 moves about the arena by riding on a comically small unicycle. He can make something more practical by combining it with his oversized ink roller, however.
• Star Wars Droidworks has several locomotion options for wheeled droids, including one that's a non-magnetic unicycle, which is useful for avoiding being caught by electromagnets, and another as a streamlined tricycle.
• Robot Medics in Team Fortress 2 are the only robots in the game to not use legs, instead opting for a single wheel.
• Roadkill Rodney, a robotic enemy from Teenage Mutant Ninja Turtles: The Arcade Game and its ports. Not only could it stay upright on one wheel, but it could send out an electric cable to try to zap a turtle. Whether or not it succeeded, it never fell over until it was defeated.
• In Tiny Toon Adventures: Buster's Hidden Treasure, the robot enemies in the factory levels stand on one wheel.
• In the Super Famicom Product as Superhero game UFO Kamen Yakisoban: Kettler no Kuroi Inbou, riding the Yakisoban Unicycle (a non-action toy in the commercials) provides Temporary Invincibility.
• Mettaton's standard form in Undertale is a rectangular body balancing on a single comically tiny wheel.
• Wildstar has the Grinder mounts and the Uniblades, preferred by the Exiles and Dominion respectively. They are interesting both in the fact that while they have one wheel, the rider's placement varies. With Grinders, they sit on a support out in front of it, while the Uniblades have the riders on a strut behind the wheel. Also, both technically could be considered cheating; they use antigravity to keep stable and prevent themselves from tipping.

Webcomics

• The eponymous The Automans Daughter first appears riding one, at a "wheeler's bar".

Web Original

• Escape Plan B is a Steampunk artwork, where the protagonists are fleeing on a one-wheeled vehicle from a Humongous Mecha.

Websites

• The robot mascot for the website/image search engine TinEye is a one-wheeler. Also a case of Invisible Anatomy, since that wheel is not visibly linked to the rest.

Web Videos

• In Campaign 3 of Critical Role Sam plays the automaton Fresh Cut Grass, who gets along on a single wheel. He's implied to have to lift himself up stairs step by step, but can navigate them thus far.

Western Animation

• The Adventures of Jimmy Neutron, Boy Genius: Jimmy Neutron designed his android little brother Brobot this way.
• Buzz Lightyear of Star Command ends by introducing a love-interest for XR: a robotic personality named 42 living inside Star Cruiser 42. By the end of the episode, 42's personality is "surgically" removed from the cruiser and placed inside a short, humanoid, robotic body with a single wheel as its mode of locomotion.
• Starting in Season 2 of Code Lyoko, Ulrich has the Overbike (pictured above), which also flies.
• DuckTales:
  • Fenton Crackshell of 1987's DuckTales and Darkwing Duck gets around this way as Gizmoduck. Besides the question of how he stays upright, none wonders where his feet go when he transforms.
  • Fenton Crackshell-Cabrera of 2017's DuckTales also has a single wheel at the base of his Gizmoduck armor, although the armor is at least bulky enough that it's believable his feet fit above it.
• Speedors in Legends of Chima are one-wheeled vehicles that are regularly used for races.
• Ready Jet Go!: In "Try and Try Again", the kids try to put one wheel on Jet 2, but it doesn't work. The episode also shows Bergs riding a Penny Farthing bicycle.
• The title hero of Snyder-Koren Productions Roger Ramjet has a few episodes facing the Solenoid Robots, all of which balanced themselves upon a single wheel.
• The Muni Mula men from The Ruff & Reddy Show balance on a single wheel.
• Spiral Zone has the Zone Rider, a one-wheeled motorcycle used by, well, the Zone Riders.
• The heroic characters in the Poet Anderson: The Dream Walker short have bikes of this kind.
• Young Justice (2010): In "Schooled," Robin turns his regular looking motorcycle into a one-wheeled motorcycle AND a small flying drone. Later, in "Royal We," Artemis rides a one-wheeled motorcycle on the covert mission to Markovia.

Real Life

• The unicycle, of course.
• Behold, the Honda UNI-CUB.
• A self-propelled unicycle has been developed. Like a Segway, all the rider need do is lean forward. The unicycle more or less self-balances.
• The Uno-Wheel Motorcycle, the first fully functional one wheeled-motorcycle. Though technically it has two wheels side-by-side, it looks quite close to Code Lyoko's Overbike.
• Along the lines of the Polarian mentioned under Literature the Ballbot is a robot that balances and moves on a single ball.
• The BB-8 droid from The Force Awakens is a practical effect, meaning that such a robot actually does exist in real life. You can even buy your own smaller licensed version.

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