A self-balancing unicycle is a type of unicycle, that is an electric vehicle, that uses sensors, gyroscopes, and accelerometers in conjunction with an electric motor to assist a rider with balancing on a single wheeled vehicle. As of 2015, several models were commercially available. 
- 1 Control theory of the self-balancing unicycle
- 2 Early work
- 3 Law
- 4 Human-ridable self-balancing unicycles and commercialization
- 5 Similar-looking vehicles that are not true unicycles
- 6 Fictional self-balancing unicycles
- 7 OpenSource firmware
- 8 See also
- 9 References
- 10 Further reading
- 11 External links
Control theory of the self-balancing unicycle
The problem of creating a self-powered unicycle that balances itself in three dimensions, is an interesting problem in robotics and control theory. The theoretical work on the unicycle problem is complemented by work on the construction of actual mechanically ridden unicycles.
To first order, a self-balancing unicycle can be considered as a non-linear control system similar to that of a two-dimensional inverted pendulum with a unicycle cart at its base: however, there are many higher-order effects involved in modelling the full system. Rotation of the drive wheel itself can provide control in only one dimension (i.e., forwards and backwards): control in other dimensions generally requires other actuators, such as auxiliary pendulums, reaction wheels, or control moment gyroscopes attached to the main unicycle pendulum.
A number of academic papers have been published that either investigate the problem theoretically, or document laboratory-scale prototypes. A number of student and amateur engineering projects have implemented similar designs. Self-riding self-balancing unicycles are necessarily two-axis balancing devices.
Laws in some places fail to address this new form of transportation. However, there are provisions in place regarding the use of electric mobility devices for the disabled. Andrew Smiley has formed a Group on Facebook, "Electric Unicycles of Downey, California" and has advocated for the use of such devices inside of stores through the Americans with Disabilities Act of 1990.
Human-ridable self-balancing unicycles and commercialization
Single-axis self-balancing ridable unicycles
A number of self-balancing unicycles have been created which are self-balancing only in the forwards-backwards direction, and still need a human being to balance them from side to side. Trevor Blackwell's Eunicycle is an example of a human-ridable single-axis self-balancing unicycle. In 2009, RYNO Motors of Portland, Oregon created a one-wheeled electric motorcycle called the Micro-Cycle. According to the company, a commercial version is scheduled to begin shipping in April 2014. In 2008, Focus Designs released the first commercially available self-balancing unicycle. In 2011, Inventist marketed a 11 kg stand-up, seatless version called the Solowheel. Because they have a weight, size and carry handles ideal for the last mile commuter, by 2015 this invention had spawned an entire category of increasingly popular "micro-unicycles" of varying quality and design.
The RIOT wheel is a ridable single-axis self-balancing unicycle with an unusually low centre of gravity, with its rider in front of, rather than on top of its single wheel, balanced by a counterweight within the wheel.
True two-axis self-balancing ridable unicycles
A two-axis self-balancing unicycle balances itself both forward and backward, and also side to side.
- In 2003, Bombardier announced a conceptual design for such a device used as a sport vehicle, the EMBRIO. It is unclear whether Bombardier ever intends to create a working prototype of this vehicle.
- Aleksander Polutnik's Enicycle (2006) is probably the first two-axis balancing human-ridable unicycle.
Similar-looking vehicles that are not true unicycles
A number of vehicles are almost self-balancing unicycles:
- The Segway is a vehicle which is capable of automatically balancing itself in the forwards-and-backwards direction, but is a dicycle with two parallel wheels, similar to the later self-balancing two-wheeled board rather than being capable of balancing from side to side.
- In 2006, researchers at Carnegie Mellon University developed a 2-dimensional inverted pendulum that balances on a ball rather than a wheel.
- Two-wheeled self-balancing (mobile) robots 
- The Uno, a vehicle that superficially resembles a self-balancing unicycle but is actually a dicycle with its two wheels very close together
- The Honda U3-X looks like a self-balancing unicycle, but balances on a powered Omni wheeI rather than on a single wheel
Fictional self-balancing unicycles
- A self-balancing unicycle was described in 1969 in The Man From R.O.B.O.T., a short story by science fiction author Harry Harrison.
- Fenton Crackshell, a Disney character, is depicted wearing a robotic unicycle suit.
- Demolishor, a Decepticon from the 2009 Transformers sequel, whose robot mode is a gigantic robotic unicycle.
- The "tumblebugs" in The Roads Must Roll
- The protagonist in the Flash browser game, Little Wheel.
- Thor, fictional inventor of the wheel and the comb, of the comic strip B.C..
- Securitrons from Fallout: New Vegas.
There is an initiative to develop from the start an OpenSource firmware for the cheap generic electric self-balancing unicycles. Some users are also looking to know more and develop OpenSource electronic boards and 3D printed shells for modding theirs self-balancing unicycle. Please see the project page here: https://github.com/generic-electric-unicycle/documentation/wiki
- Charles F. Taylor working prototypes 1939-1964
- Control moment gyroscope
- Inertia wheel pendulum
- Inverted pendulum
- List of cycling topics
- Self-balancing two-wheeled board
- Segway PT
- Rice, Vincent (26 January 2012). "Version 2.0 of Focus Designs Self-Balancing Unicycle now ready for primetime". GizMag. Retrieved 25 September 2014.
- "ElectricUnicycleReviews.com :: Self balancing electric micro unicycle reviews :: Airwheel, Firewheel, Gotway, Inmotion, IPS, Legway, Ninebot One, Rockwheel, Solowheel :: All Reviews By Brand". electricunicyclereviews.com. Retrieved 2015-12-27.
- http://rynomotors.com/ Micro-Cycle — archived RYNO Motors 'blog page
- About RYNO Motors page.
- Slide 3 Slide 3 (2013-04-17). "Self-Balancing Unicycle | Focus Designs, Inc. | The SBU is the coolest light electric vehicle on the market. The gyro-stabilized SBU contains full-frontal nerdity!". Focusdesigns.com. Retrieved 2013-04-26.
- Inventist Solowheel
- Solowheel: self-balancing last mile transport for the upstanding commuter.
- Last Mille Club, unicycle archive
- Kaiman, Jonathan (May 30, 2015), "For Solowheel maker, a patent rights nightmare in China", The Los Angeles Times
- Carnegie Mellon Press Release, August 6, 2006 – "Ballbot"
- Modelling and control of a flexible two-wheeled self-balancing mobile robot
- Flexible two-wheeled self-balancing mobile robot, 9th IFAC Symposium on Robot Control (2009)
- A Two-Wheeled Self-Balancing Robot with the Fuzzy PD Control Method, Mathematical Problems in Engineering Journal
- SELF-BALANCING MOBILE ROBOT TILTER, FAMENA 2012, Vol. 36 Issue 3
- ANALOG — Science Fiction/Science Fact, Vol. LXXXIII, No. 5, July 1969, pp. 120-151. Illustrations by Peter Skirka.
- "Little Wheel - game at". Fastgames.com. Retrieved 2013-04-26.
- S. V. Ulyanov et al. Soft computing for the intelligent robust control of a robotic unicycle with a new physical measure for mechanical controllability. Soft Computing Volume 2 Issue 2 (1998) pp 73–88.
- Zenkov, DV, AM Bloch, and JE Marsden  The Lyapunov-Malkin Theorem and Stabilization of the Unicycle with Rider. Systems and Control Letters, Volume 45, Number 4, 5 April 2002, pp. 293–302(10) (postscript format available here )
- Zenkov, DV, AM Bloch, NE Leonard and JE Marsden, Matching and Stabilization of Low-dimensional Nonholonomic Systems. Proc. CDC, 39, (2000), 1289-1295. (pdf format available here )
- Sheng, Zaiquan; Yamafuji, Kazuo: Realization of a Human Riding a Unicycle by a Robot. Proceedings of the 1995 IEEE International Conference on Robotics and Automation, Vol. 2 (c1995), pp 1319–1326
- A. Schoonwinkel, "Design and test of a computer stabilized unicycle," Ph.D. dissertation, Stanford University, California, 1987.
- Johnson, R.C. Unicycles and bifurcations, American J. of Physics, volume 66, no.7, 589-92
|Wikimedia Commons has media related to Solowheel.|
- Bombardier Recreation Products EMBRIO one-wheeled recreational vehicle concept design
- The loonycycle, which superficially resembles a simple robotic unicycle, but uses side-thrusting fans for lateral balance
- Rosie the Robot - a Question of Balance Ken Perlin's page on robotic unicycles, with designs and java applet examples.
- The Unibot: a working robotic unicycle built for a university engineering project (with movies)
- Robotic Unicycle: Ongoing project
- Micycle (reports, papers, photographs and movies)
- "Unicycle riding robot unveiled". BBC News. 24 September 2008. Retrieved 2008-11-24.