[Al Skierkiewicz]

Crab steering should be no harder than any other steering and perhaps more easy. You need to know how far the wheels have driven (preferably more than one to increase accuracy), which direction the steering is turned and where you want the robot to be at various intervals. The big variables occur when you run into objects on the field like goals and other robots. With other steering methods you have to compensate for turning radius when moving in other than a straight line.
As far as travel, we have used wheel encoders, either scratch built optical or off the shelf rotational encoders. The data is then used in calculating the distance traveled by incorporating wheel circumference and rotations. Steering is a simple pot but you should have used that already for feedback control with manual steering. A gyro will help you to maintain preset way points and can help in collision correction. We used one to great effect during 2003 when climbing the ramp in auto.