There are encoders and then there are
encoders. FIRST Choice had one of them, the AS5030, available as a demo board. It featured 256-step encoding of a full rotation using a rotating magnet as input. Electronic resetting of the zero point is one of the features, along with magnetic field strength was available.
You can also convert a standard pot into full rotation as long as it's not one of the miniature variety. You just have to support the wiper with an insulator bridge and do a little strategic filing and careful re-assembly. It won't increase the measurement range but it might simplify the construction some. I suppose you could overlap two of them, but I haven't tried it.
The pot route may be easier to understand, i.e. (dare I say it?) more instructional. An added plus is the ability to brag that your 'bot is on pot.
