There are three possible solutions:
1. add a set point, something like a microswitch being pressed when the wheel is at angle 0. For this solution the wheels would have to do an initialization process on the beginning of each match (turn around until microswitch is pressed).
2. Save your wheels last positions in the cRio memory, possible, but not really a good solution.
3. Third time's the charm - use absolute sensors (not incremental encoders) such as Potentiometers (one or multiple) or absolute encoders (see
http://usdigital.com/ for MA3 or MAE3).
have fun programming.