This mixer extruder is a prototype made with a single motor that handle multiple materials taking four 1.75mm colored filaments and combine them out of a single nozzle. That system is 3D printer equivalent to CMYK traditional printers.
The mixtruder is a combination of mixer and extruder filaments using only a driving motor for extrusion and servos for mixing various filaments. Initial versions do not require additional circuitry to that already used RepRap 3D printers since they are designed to use electronic RAMPS, sanginololu, SAV , which already have support for servos.
All details at http://mixtruder.com