[DonRotolo]

For distance you'll do fine with encoders/GTS, but the slip when you turn will be too variable to accurately keep track of the amount of turning. Also, the errors will accumulate if you're not careful.

Turning is best sensed with a gyro and timer: If the rate gyro says you're turning at 15 degrees per second, and you do that for 6 seconds, you've gone 90 degrees to a fairly high degree of accuracy.