[DonRotolo]

To measure distance traveled, a topic known as odometry, one would normally use a sensor that measures how many turns one or more wheels have made.

An optical encoder was included in the KoP for this, you mount a small wheel to a 1/4" shaft and it delivers something like 250 360 pulses per revolution. Since it has two signals you can also tell whether the wheel is traveling forward or backward. There are other ways to sense rotation, but most teams use the optical encoders supplied.

Naturally the accuracy of such a system depends on many factors, most important a relative lack of slippage between the wheel and the surface on which it travels. If you anticipate significant slippage, an unpowered 'fifth' wheel can be used (google it)

Wiring up the sensor is not difficult - power, ground, signal A and signal B. We wire up power and Signal A to one digital I/O on the sidecar, and ground and signal B to another digital I/O. I'm not a programmer, but I believe there are routines in every language for handlingt his data stream. They're a bit finicky (as judged by the number of CD posts asking for help) so use care to ensure it works first time.

Good luck, you are on the right track away from dead reckoning.