Direct drive extruder for Printrbot with Ubis hotend, NEMA 17, MK8 gear

Remake to fit with Printrbots and Ubis hotends.
All Printrbot Jr owners should use the base jr
http://www.youtube.com/watch?v=Xb7hPECXst4

quick filament change
http://www.youtube.com/watch?v=V1FkHT_6MmU

Update 11/2013:
added a baseversion with fanmount. Sometimes the filament got stuck in the lower basetube. With this 60mm fan I had no issues.
download the counterclock version if your mk8 gear turns counterclockwise to extrude, otherwise download the clockwise version