This is a great learning project. I've done a few of them with our 599 kids over the years.
Have you set any constraints on cost and hardware yet since this will help a lot in trimming down your design choices?
We tried a cheap version which used donated wheel chair motors, freescale demo board (with built in 3 axis accelerometer) and a silicon sensing rate sensor. The only major expense was a Sidewinder motor controller
http://www.robotcombat.com/products/RP-SWDR.html.
We found it useful to build a Vex pendulum robot to develop and test the software before using it. This project in itself is very instructive especially if you want to get into the control theory behind the derivation of gains required to stabilize the robot. We did it both with a vex controller and a freescale demo board. Check
http://www.youtube.com/vamfun channel for a few videos. There is also software and discussion thread on the vex forum
http://www.vexforum.com/showthread.php?t=1593 . A white paper on the theory and matlab simulation is also on the vex site
http://www.vexforum.com/showthread.p...ht=white+paper.
I have an extensive inverse pendulum and Segway data base so feel free to contact me if you would like some good papers or have any questions. Email me at
vamfun@yahoo.com. This is also my AIM screen name and I chat a lot with the kids there.