Here are some pictures from our 2001 robot. We made a sandwich of three aluminum plates, the base, the rotation ring, top plate or gear plate. The base had a 1/4" groove milled in at a specific diameter (20+ inches, it was 6 years ago). The rotation ring had a groove machined in the bottom at the same diameter as the base and a groove in the top machined at a slightly smaller diameter if I remember correctly. The top plate had a groove machined at the same diameter as the top groove in the rotation ring. The grooves were only 0.060" or 0.090" deep. We filled these grooves with 1/4" ball bearings. The rotation plate had the old window motor attached to it. I had measured the gear on the window motor and then in cad created an internal spur gear that was the size we wanted. We slapped the plate on the cnc and let it cut the teeth for the top plate. To check our position we created a lexan gear that attached to a pot located on the rotation plate. The whole system was very smooth, stable, easy to control. On last years robot (2006) we made a similar turret with a few modifications and improvements. I can't find any pictures of that one yet, but if I do I will post them. Last year we had the pleasure of watching our robot tip over going up the ramp and having the "Head" break off, sending ball bearing flying all over the field.
Zip ties make horrible bearings, but they do keep you in the game.
