one more question. When i read about the segway it said that there different speed settings. i.e. a certain key is used when the rider wants he maximum speed to be for example 10 miles/hr. in that case how does the segway deal with a passenger who leans forward a little when it already maxed the speed. cause if it does not accelerate a little the segway will not be able to balance the moment created by gravity and the passnger will head face first into the ground
i was over simplifying a little.
if you lean way forward while going full speed on a Segway it readjusts to make sure the centre of mass is directly above the wheels (or a little in front to counteract drag).
so the "handle bars" in this situation would tilt back but the center of mass is still in the same place.
once you have a bit of practice though you stop fighting it and let the Segway point straight up.
this also means your face is not sticking way out in front and the first thing to crash into a fellow Segway rider coming round the corner at you...
i have tried to make a Segway fall over forwards and backwards and as long as it has good traction it really can't be done.
the sensors and drive motors can react more quickly than you can move your weight.
on slippery surfaces all bets are off though.
the worst crash i witnessed was one wheel on a piece of plastic packaging during rapid acceleration. one wheel accelerated quickly while the other just shot out the packaging an stayed put. the rider left the Segway at a suitably comical angle.
if both wheels skid together which is more normal it just dumps you on your arse.