We just followed from the original JVN picture and eyeballed it, selecting materials from what spare VEX part we had. JVN's version is much more compact than ours:
http://www.chiefdelphi.com/forums/sh...ad.php?t=70627
Here's an OK close up of ours:
http://www.chiefdelphi.com/media/img...4275b627_l.jpg
most browsers will enable you to magnify the image, or just save it and magnify with software
Essentially, you just need to build a 12 stage reduction using:
4 VEX plates or chassis rails with appropriate width and length
12 12-tooth gears
12 60-tooth gears
1 big wheel on input side
1 small wheel on output side
stand-offs
shaft collars
fasteners
spacers
shaft to size (only one shaft runs all the way through the gearbox - the one at the bottom)