Once I moved from printing in PLA to printing in XT, I started to get annoyed by the increased blobbing, stringing, and layer unevenness that came from the compression of the filament in the bowden tube. (XT is less stiff than PLA, which was clearly causing back pressure and reduced retraction efficiency.) Consequently, I started looking for direct-drive options for Delta printers, and the only promising option seemed to be the Ultibots Micro Extruder. Well reviewed though it is, it 1) seemed rather large in Z, and 2) plastic printed extruder components have failed on me in the past, due to the temperature difference between where steppers can operate safely and where plastics can avoid significant creep.I also am a fan of Printrbot's geared extruder design, and had previously designed my own minimal housing for it using Shapeways printed stainless steel. So, with those parameters in mind, I quickly sketched out a combined hotend-mount, direct drive extruder, and mag-ball based carriage to start down the path of a minimally sized, rugged, precise, highly integrated effector. The result works well and can be cost-effectively printed from Shapeways stainless steel (or likely their other metals, if you prefer, though they are more expensive).