[Al Skierkiewicz]

Ian,
As Dave said above we did some rather extensive research into direction finding and compass usage. Besides the fact that they are somewhat expensive, they cannot distinguish the earth's magnetic field when placed within the robot frame with all the DC(magnetic) motors and various metals in the construction. There is also so many variables when used inside buildings due to electric fields and metals in the roof, walls and floors. Although they look very good on the surface they became to difficult to implement.
Sorry.
If you are intending on using a feedback system from the OI to the robot, teams have been using the gyro for years to do that so there is a lot of info around. Remember that if the sensors are initialized correctly, they should track fairly well over a two minute match.