I would suggest trolling through back issues of S&T for articles about them. I can distinctly remember 3 over the past 15 years. I made a stepper motor controller/corrector and have had very good luck with it. One thing I would definitely advise is to use a crystal for the reference clock instead of an RC oscillator. I have the RC circuit and according to the data sheet it's fairly stable over a normal temperature range but I still notice drift. The benefit is you don't have to divide down an RC oscillator if you chose the R&C correctly.
The drive corrector plans I remember that deal with AC motors are from the late '70s or early '80s. They really aren't very complex to build...
Steve Dillinger fmicos!dillinger@uunet.uu.net