I've started a new project that is based on an excellent instructable by XenonJohn. http://www.instructables.com/id/Easy-build-self-balancing-skateboardrobotsegway-/
I spent a weekend putting together a prototype on a piece of 3/4" plywood and tweaking the code to work with the Accelerometer/Gyro that I was using. The code was the most difficult part.
Major parts I am using are: * 2 - 250W motors (from a Razor E300) * 2 - 6" wheels (from a Razor E300) * Sabertooth dual 25A motor driver * Arduino (this does all of the processing of the signals from the Accelerometers and Gyros and determines the signal to send to the motor controller.) * MinIMU-9 v2 Gyro, Accelerometer, and compass * 2 - 7aH Sealed lead acid batteries
I even took this board out in front of my house and was able to ride around on it. But I don't have turning hooked up yet.
This video shows that it is balancing well on it's own. The wire I'm holding is for the dead man switch to cut power to the motors if something bad happens. http://www.youtube.com/watch?v=ABNQpeOsF20
Next will be adding a skateboard deck, turning, LED lights, buzzer, proximity detection, etc.
More to come on this.......