The 2013 kit of parts (or maybe it was FC) provided us with a magnetic rotary encoder.

  * anymark part number may have been fc13-062
  * manufacturer part number maybe AS5145B
  * datasheet for AS5145H / AS5145A / AS5145B: http://www.ams.com/eng/content/download/50206/533867/34237
  * https://wpilib.screenstepslive.com/s/3120/m/8559/l/91404-using-the-as5145b-magnetic-encoder-with-the-frc-control-system