So here's a bit of explanation about the capstan system.
First, of course, the drive gears and chain can be replaced by whatever mechanism you want... I just felt like drawing gears. You can use a belt with pulleys, or a worm gear, or even just friction wheels.
The capstans themselves are just rollers from a VCR or something similar, with the outer edges milled down to 1/8" smaller diameter than the centres. That's why I mentioned that it's important to grind the hinge plates down to match the hoop curvature. When the hinge gap hits a roller, the plates take over supporting the hoop on the outer sections of the capstan. You also have to make sure that the latch doesn't protrude past the hoop edge, or else it will cause a bump.
It seems necessary to post a side view of the wire feed system, but I'll go ahead and describe it while I'm here. It's a totally separate unit that bolts into place when you want to load the hoop. The axle is interchangeable to match whatever factory spool you use. The previous sketch of it is actually 'inside-out', in that the spool faces away from the hoop rather than toward it as shown. The only parts that protrude into the hoop area are the top of the feed tube and the slider lock pin. The lock pin goes through the slider anchor loop to prevent the slider from rotating with the hoop during loading. The feed tube guides the wire from the spool to the entrance/exit hole in the slider.
To load the spool, you first open it and place it around the toroid. Then you run the wire from the spool up through the guide tube. Rotate the hoop until the latch is on top. Bolt the feed assembly into place. Thread the wire through the holes in the slider as shown in the slider sketch, then open the hoop again and clamp the free end of the wire into the latch gap. You might have to double it over a couple of times to get a good grip if the gap is too wide. Snip the exposed part off so it won't interfere with the capstans. Insert the slider into the hoop with the anchor ring around the lock pin. Flip your switch to the 'load' position to rotate the ring away from the toroid (clockwise in the sketch). The wire should freely unspool from the loader, through the slider, and into the hoop. When you have as much as you want, or reach the hoop capacity, shut it off. Cut the wire between the spool and the feed tube (to leave a long end) and remove the feed assembly.
I'll go start on the side view now, but I might not have time to finish it before I have to go to work.
edit: Okay, here it is. I didn't bother labelling it.
http://img244.imageshack.us/img244/5773/feedmechanism1td6.jpg