Carriage for Kossel Mini (replaces ball rails)

Building a Kossel Mini? If you can't find those ball rails spec'ed for it, don't want to wait until the [Kossel Pro kickstarter](http://www.kickstarter.com/projects/ttstam/openbeam-kossel-pro-a-new-type-of-3d-printer) ends, and want to save over $50, this part gives you another option.

This is a Cerberus Pup-style carriage for Kossel Mini. It provides smooth motion with low cost (~$70 for 3) on OpenBeam, using [Graber Dual 623 V rollers](http://3d.grabercars.com/?product=dual-623-v-roller).