The RepRap style filament based printers have expanded the capabilities of hobbyists all over the world. Note, this project grew from our work with full color print heads, and the filament mixing motor outputs are labeled on E0, E1, E2, E3, and E4.  Most printers should use FreeCAD, Slic3r, Printrun, and our Marlin firmware (even if using a single extruder).