May 2011: This instructable is now quite old (relatively) and I could now rebuild this project more simply with an Arduino as the controller.
I am currently working on a unicycle with the same OSMC motor controller and an Arduino. When I get that to work I will also add the code to this instructable as the principles will be almost the same (one wheel one motor).
After reading a Make magazine article on the self balancing unicycle of Trevor Blackwell I thought about trying to build a one wheeled skateboard style device. I then found a self balancing skateboard on the net built by Ben Smithers and decided I would definitely have a go at this.
For more information and pictures of my earlier designs please go to:
Trevor Blackwell unicycle and SegwayTM clone: http://tlb.org/scooter.html
Ben Smithers skateboard which inspired me to build this one:
Also check out this self balancing unicycle:
and this video of same machine from the Gadget Show (wait for the sponsor message to pass)
Also, many people have tried to build self balancing robots with 2 wheels. There are many on the web. If you do this using a gyroscope, accelerometer, microcontroller and geared motors from a robotics store, you will spend almost the same amount of money as this machine cost to make. The mechanical parts are kart based and often available on ebay. Some robotics mechanical parts are pretty expensive. I thought if I was going to do the "self balancing" thing then I might as well make a robot I could ride!
VIDEO 3/1/09 below.
Video shwing stability and ability to cope with small obstacles. I have since lowered the ride height to make it more controllable in terms of steering at speed.
This is the latest (March 09) lighter weight version with same power as the monowheel but split between 2 motors + same battery power using lighter LiFePO4 battery. Now based on a real skateboard and has 2 wheels so can turn on the spot. Also only 30lb so you can pick it up easily: