This design has been superceded by Ron's Compact Extruder Mark II: http://www.thingiverse.com/thing:24219

This is Ron's Compact Extruder modified to sit on the Ultimaker's XY carriage. I haven't tested the max speed, but I am able to print at 100mm/s without any trouble. The main advantage is that by removing the Bowden tube from the extruder, there are fewer messy strings after each print.

Note: This version of RCX is a mirror image of the original. This allows the lightweight stepper motor to be placed as close to the center of the carriage as possible. Additionally, and as a result, the direction of the extruder stepper does NOT need to be changed in the firmware.

Note 2: I've added two OpenSCAD files. The rcx.scad file replaces Ron's rcx.scad. The ultircx.scad is just a wrapper that calls it. (Put all of ron's files in a subfolder called RCX, and ultircx.scad will then know where to find it).