Balance while turning?

[sanddrag]

I am looking to build a Segway type vehicle of my own and I've come across I question I can't quite seem to answer. Simply put, while moving in a straight line or standing still a vehicle of this sort balances because the more it tilts the motor the motors compensate. But what happens when you are turning in place as in one wheel rotating the opposite direction of the other? I have ridden the real Segway and it maintains it's balance exceptionally well while performing that maneuver. I was just wondering what the logic was behind that. Going in a straight line, the movement is explained as a controlled fall. How can it maintain balance while turning on it's axis because there is no single direction of falling for which to compensate? Or it it even falling at all while turning? If you could provide me an answer soon that would be great because I'm currently figuring out everything I will need for my project.

One more thing - does 6 mph seem okay as a max speed for this vehicle? I know the real one does 12.5 but it has some really speacial stuff.