Bowden tube feeder with filament release mechanism  
This is a Bowden tube direct drive filament feeder for 1,75mm filament. (User Kert made a remix for 3mm fillament using a geared stepper over here: http://www.thingiverse.com/thing:306532)
The great thing of this feeder is that it has a quick release mechanic to remove the tension of the filament on the extruder motor. This way you can easily remove en feed filament by hand.  
I've made a complete instruction video how to assemble the feeder and explanation of the inner working mechanics:http://www.youtube.com/watch?v=ZsNm0UfQsyQ
(One mistake in video: the two 45mm M4 bolds should be 50mm)  
Also included is a filament spool holder for extrusion bars  
If you use it, please share a picture!