For measuring steering angle on swerve, absolute encoders should be used. Ether listed a few. For 2011 we used the Vishay 981's. They performed well. Automation Direct has a plastic beam coupler that is inexpensive and allows for some misalignment and will help protect the encoder. In 2010 we used the Cherry AN8's. They are a true non-contact encoder and also worked well. The absolute encoders that have been listed are analog output. They output a voltage between 2 voltage end points. These end points are dependent on the analog break out's 5 volt regulator. The .5 and 4.5 volts are common end points. If the supply voltage is above or below 5 volts these endpoints will move. Keep this in mind when programming the 0 - 360 transition. The US Digital are 0 - 5 volts. Their output gets sloppy at the rails (0 - 5). That coupled with their susceptibility to electrostatic discharge are the reasons we did not use them. Pay attention to the electrostatic rating of these sensors. A discharge can mess up some of these sensors and if your encoder goes your robot will look like it is having a Grand Mal seizure. Choosing a sensor that is automotive qualified is a good idea. There are also absolute sensors that output a 10, 12 or 14 bit reading over a SPI buss. We are looking at some of these for this year. The advantage is that on some of these the the 0 - 360 transition can be programmed leading to simplified calibration procedures. Last, we paid under 30$ for our sensors in 2010 and 2011. These same sensors are in short supply and the price has more than doubled. Must be a Japan issue from the earth quake. If they will be needed in 2012, then keep an eye on the availability and price this fall.
As to swerve, Our team believes that independent 4 wheel drive and 4 wheel independent steering modules are the only way to go. I don't have time to go in to a rant why we believe this but this link will show what we have done for swerve.
http://wiki.team1640.com/index.php?t...II_Drive_Train