Removing the bowden tube and putting the extruder directly on the head.This is not just for fun, but to make printing of flexible filament possible (Filaflex, Ninjaflex for example but it can apply to any filaments that don't like long bowdens).The final print result is astonishing, no underextrusion whatsoever and perfect layer adhesion.Printing at 25mm/min gives good results. Faster than that makes the heavy head a bit shaky and degrades print quality.For my setup I have to increase flow in Cura or in the machine to 140% (due to the smaller diameter at the teeth of my hobbed screw)See it working:http://youtu.be/EIO-JXnnoNcIt is derived from the famous "Greg's-Wade's-Taylor's-Someone's extruder" and uses the original stepper from the Ultimaker.The whole thing is mounted on top of the moving head and does not need to disconnect the sensor or the heater. I still haven't found a place to mount the small ADC board so I leave it hanging from its wires at the moment.All you will need is a hobbed bar / bolt (I use the excellent Hyena from" Arcol.hu" but any 8mm hobbed/knurled bolt with thread on both sides will do just fine) and 3x 608 bearings (skateboards/inlines). You ill also need a small bit of bowden tube (I used a 4x6 aluminum tube, approx 70mm long so it doesn't need to be flexible)And of course some assorted M3 and M4 bolts + 2 springs. The rest is printed.The running direction of the motor should be reversed. For me this is done by a custom crossover XLR cable as I use XLR connectors to disconnect the motor. So, no extra cable= forward, normal Ultimaker extrusion and with the extra cable (provides the needed extra length)= reversed direction. Or you can just cut the cables and add a screw terminal and swap the cables in each pair.I provide the main body with integrated print support that will save you a bunch of filament and printing time.This works pretty good now but feel free to improve, comment and share. I include the source files (Solidworks 2012). I know they look quite ugly but it's hard to make a clean source when you don't know how it's going to look like at the end.Some STL files are not correctly oriented yet, so take an extra look before printing!This modification is not hard to install and is fully reversible (no changes done on the original parts). It takes approx 15-20min to swap between direct and original extruder.