[KenWittlief]

actually the balancing algorithm on a Segway is not much different that the cruise control on a car. Sensors detect the orientation of the platform and the rate at which it is starting to tip, and the motors respond to keep the Segway level

just like the cruise control on a car adjusts the throttle to hold the car at a constant speed - the Segway holds a constant level.

I dont have personal knowledge of the algorithm used, but you can make feedback systems tight or loose. If its tight it will quickly cancel out all error. On the Segway, that would mean as soon as you shifted your weight (lean forward) it would instantly compensate to stay level, moving very little.

I think the feedback on the Segway is selectively loose - when you lean forward it compensates to keep you from falling over, but not completely, so the platform ends up moving forward - sorta like its perpetually falling