[KenWittlief]

Great post by TedP - only thing I would add is the motor speed is not the only way to go

for our auton mode we were more concerned with robot heading, so using a yaw rate sensor was the easiest solution - for most driving situtaions getting the robot pointed in the right direction is the trick, how fast it move (preciesly) is of less concern

you can calculate how fast your bot is turning by having speed sensors on both wheels, but its much simpler to plant a yaw rate sensor on your frame somewhere and read it directly.

BTW - if anyone is wondering if this stuff is worth the trouble- yes! our auton mode worked very well when our team coach remembered which 'left' to set the switch to (left or the other left)

and at Buckeye our team won the Johnson & Johnson quality in controls award - I think not so much because of the PID closed loop feedback we had on our steering, arm elevation and arm extension, and the use of IR sensors - but because our students could explain so well to the judges how it all works.

sophestication is good - understanding is excellent :^)