I'm in the process of making one of those out of an arduino! But it's only about a foot in diameter...
Anyway, these drives are generally called "killough" or "kiwi" drives. The code I used is based off of what I found here:
http://www.vexforum.com/showthread.php?t=7596
You'll have to do some thinking to understand and convert to your native programming language, but hopefully that will help.