This sounds like a page right out of my playbook, and I thought I was the only one! The only real difference is that I use a DIY "Lazysusan", turned by a barbeque rottiserie motor mounted near the outer rim. These barbeque motors have plenty of torque (they're designed to turn a 20 lb. Turkey) and they already have a gear reduction system that delivers about 3 RPM. That's about half the speed of my microwave turntable (Slower Is Better!).
The actual rotating speed of the turntable is determined by the size of the drivewheel attached to the motor that actually comes in contact with the underside of the turntable (near the outer edge). For example; a 2" wheel gives about 18" of travel per minute, if it's mounted 18" from the pivot point (on the rim of a 36" turntable) it will deliver about 1 revolution every 6 1/4 minutes -SWEET!
The biggest challenge for me was figuring how to build a round grow area (to get the best light reflection). I settled for a simple cylinder of Reflectix - maybe you can do better.
EDIT: Oh, I almost forgot! Your light should hang way off-center. I hang my lights so that 1/2 the total plant area is "inside" and 1/2 the area is "outside" of a point directly under the lights. That sounds a little confusing - let me put it this way. A 24" circle is about 3 sq. ft.; I would hang my lights so that it divides the inner 1 1/2 sq. ft. circle from the outer 1 1/2 sq. ft. "donut shaped area" (at a point about 8 1/4" from the center). Of course, these numbers change with different sizes - just hang your light at the "1/2 Total Area Mark".
