Detailed description/instructions: http://cdaringe.net/cossel-bowden-extruder-v2/
A bowden-type extruder designed as a drop in replacement for other popular bowden designs, such as Airtripper's v3 or bsp, but tailored specifically for using a geared stepper motor.
Integrated geared steppers have a different mounting hole pattern than traditional NEMA 17 motors. A popular geared stepper motor in the RepRap domain is the Phidgets 5.18:1 (1, 2) motor, which I have used as a reference in the design. The motor mounting holes are much closer to one another than on a traditional motor, forcing the extruder body to be more compact than it's non-geared counter-parts. Only a 1.75mm filament is uploaded at the moment, but if there is demand, I can upload a 3mm version. Of course, you can simply drill the guide holes out to accommodate.