The idea of being able to print with two different filaments at the same time with the SmartrapCore is very tempting… I'm working on it (it's nothing more than a work in progress, I didn't test it for real yet), with the goal of making the minimum possible change to the printer itself. So far, it seems promising, as there are only three new pieces to make : the slideX big piece to hold the two heads, a new hotends fan and Zsensor support, and (if you like) a new printing zone cooling fanduct.Update (oct. 5 2015) : I redesigned the whole thing, to allow a very necessary adjustment of hot ends relative height, plus a few extra modifications and improvements. Can't tell yet if it's really functionnal, I just printed the parts and didn't find, so far, the time to test them in actual double filament printing.Update (V. 5.0, dec. 12 2015) : many improvements, mostly about cooling (hot ends and printing zone), but most important : I added 8mm rods support! Pick the slideX that fits your setup, and there you go… ;) Also, you can have the regular 40mm fanduct or the (much better) two parts fanduct for radial fan. Both use the same fixation system, you can use either one on the same slideX.You'll need, of course, a second hot end with the exact same dimensions, extra pneufit, extra Bowden, and an extra extruder, which means another stepmotor, hobbed bolt, bearings etc. Also, the 40mm hot end cooling fan will be replaced by a 50mm one, which will be exactly the right size to cool down the twin head (you can use the spare 40mm for the printing zone cooling system with the new fanduct). Then, a few M3 bolts (35, 20, 16mm) and as many nuts. Oh… and also a second roll of filament, of course ! ;)