you can mount a central spindle and then make a disk of aluminum in the diameter you want to mount the tower on. To make the disk get a sheet of 1/4 " thick aluminum and lay out the circle. Install a bearing in the center to thread on the spindle. Carefully drill out the perimeter to make sprocket teeth . We have used a sheet of teflon under the disk to allow it to slide. A motor mounted nearby and a sprocket drive the chaiin that turns the whole thing. We did this in our champion 2000 bot and in last year's 2004 big arm machine.
Good luck.
WC
