[Gdeaver]

To expand on what Foster said, this year team 1640 went with 4 wheel independent steering. Each wheel can independently rotate 360 degrees. We used the window motors for the steering. A 3/4" 15 tooth sprocket was mounted to the window motor and a 1/8 x 1/2" neodymium magnet is centered and atached on top of the sprocket. This assembly drives the wheel module 1: 1. A AN8 360 Cherry Electric absolute position sensor is mounted 2.5MM away from the magnet. The Cherry sensor was chosen over many other similiar sensor for many reasons.
1) its non-contact.
2) It is a robust sensor being IP67 and automotive qualified. Reverse battery protected. High static discharge rated. Sealed and designed for the nasty automotive environment.
3) Cost we paid about 35$
4) The sensor is tolerant of the magnet position misalignment and distance much more than other like sensors.
5)The Cherry sensor puts out a voltage from .5 to 4.5 over the 360 degree rotation. This avoids the non-linearity at the rails (0 and 5 volts) that other 0 - 5 volt magnetic sensors show.
We looked at some other like sensors that were SPI but did not want to have the programmers work out the communications. Their plate was full enough. Analog is much more simple. The voltage output was very stable and filtering was not needed. We are very satisfied with the Cherry product. Again, if your into swerve, I would check out the link above that Foster posted. There is allot of information- pictures and white papers on what we did and how we approached swerve. Swerve- crab-pivot drive is a major under taking.