[Al Skierkiewicz]

If you want an accurate auton, you will need some kind of wheel encoder. You need to know how far the robot has traveled. We have used an imprinted wheel with black and white spaces with a simple LED/photodiode sensors (gives up to .25"-.5" accuracy) and digital pots which give much greater detail. If you are worried about slip, use more sensors and compare several. Ignore the one that is far off and average the others. Crab turns introduce less error than tank turns but can be compensated for in software. If your design is prone to high current draws during turns, it may be better to use current sense to limit drive then to use wheel tach.