This is an early prototype for a filament changer. It uses a NEMA17 and a 270 degree 9g servo. It should be much more compacted and reliable vs something like a ERCF. It current has four filaments but using a single 270 degree servo, I thing I can support 6. Two servos should handle 12. 

Parts list

NEMA 17

Servo 9g 270 degree. Most likely I will upgrade to a 17G

U groove roller wheel ball bearing 13x4mm 4pcs

micro switch from a filament runout sensor

Brass toothed gear salvaged from and old extruder

8x2.5mm ball bearing

4mm screw