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Originally Posted by Chriszuma
I would advise against using the accelerometer for computing distance. You have to double-integrate it, which will greatly amplify any inaccuracies of the data. You're better off using the gear tooth sensors, since you can hook them up to your drive train and get a direct computation of distance.
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This is a good point - double integration of the accelerometer will not be very accurate after a very short time. It can be made to work, but it is a lot more complicated than you might think at first. Angular rate sensors are nice since any rigid body has the same angular rate at every point on that body. That is not true with acceleration: you can integrate some strange positions due to centrifugal accelerations while turning, unless you know how to compensate for that.
In the past, we've always measured distance using an encoder connected to a non-powered wheel in the center of the robot. If you do not have crab steering, a single wheel along the centerline (left-right centerline, that is) should provide enough accuracy for you to do what you want.
Ideally, the wheel should be located at the turning center of your robot, but if it is a little forward or backward from that point, you will be okay. The most important thing is that it is centered side-to-side; otherwise you will think you're moving when you're turning in place.