Our team also used McMaster Part #: 18635A52 for our turreted shooter last year. This bearing worked very well... it was *very* smooth and seemed like it could support far heavier loads than our 20 pound, centrally-mounted shooter!
To control it, we simply used a single rivet to attach a timing belt, and ran the timing belt with a globe motor - we had a push-button limit switch at each extent of the turret's travel, and an encoder on the output shaft of the globe motor. I can't recall the specs on the encoder, and I'm only 80% sure that the encoder was mounted on the output shaft.
Altogether, this set up worked very well for us - it allowed us to autonomously score a couple moon rocks, too!
