[Mark McLeod]

We used a set of high quality encoders. They're on the expensive side (~$50 Grayhill series 63R), and they are overkill. We wanted one that was very dependable and wouldn't fail. We plan to use them for a long time. It's guaranteed for 10 years of continuous use at 5000rpm. They are available in a variety of counts per revolution, but digikey (newark also has them I seem to remember) only stocked two variations (128 & 256). There is also a version with a connected ribbon cable and another that's just pins. I prefer the ribbon cable. We bought the 256 variant just so we'd be able to use the higher resolution for other purposes if we so chose. 128 cpr would have still been more than enough for shaft encoders. We used plastic gears to connect them to the shafts and geared them down so we got approximately 2500 counts per second at top speed of ~9fps (~.044" per count I think).

Never failed or hiccuped. We've run them all through competition and through the summer autonomously.

P.S. I suppose I should have posted in the other thread, but I was traveling when that went by.

[edit] (There's always something I think I should add)
We do have a banner quadrature setup on the arm using a printed strip of black & white. Really more of a demonstration than a practical usage. The best resolution possible due to the arm speed, the width of the banner beam, and the length of the arm gave us about one foot, at the far end of the arm, between ticks.