Which shaft encoder to use?

[Jeff Waegelin]

I'm currently designing a holonomic drive system, and I want to use shaft encoders to measure wheel speeds. What kind of encoders should I use for this purpose? I tried looking in the DigiKey catalog, but I don't know much of anything about sensors (I'm an ME student), so I couldn't decide which type of encoder I should use.

Also, how does one mount an encoder on a shaft? I know some people use gearing for potentiometers, to increase resolution, but would you do the same thing to an encoder (if it were running at too many RPMs, perhaps)? The shaft I'd be measuring is 1/2", and spinning at 150-470 RPMs, depending on which gear the transmission is in.

Anyways, I'd appreciate any help I can get on either question (which to buy, and how to mount). Thanks!