With the release of the Kraken 4 color hot end I think a cammed extruder is a better approach than using 4 individual motors. Here I have a prototype for a 2 motor extruder that can drive all 4 filaments. Let me know what you think! I have a more extensive writeup here:
http://coherent-reprap.blogspot.com/
Wow. I’m really pleased to see someone getting to grips with this. I have a similar design on the back of an envelope that also uses cams. The principal difference is it is only for Bowden so it only requires one drive shaft and is consequently mechanically much simpler.
I assume your speeds are going to be very limited due to the weight of the cold end?
@Sanjay_Mortimer and @Joshua_Rowley need to see this.
Ooh a Kraken on a @Maker_s_Tool_Works MM2, sweet.
Looks huge , having an MM2 I know it can take that weight easily enough, tiding up those cables will be a challenge.
Look forward to seeing it in action.
This is very very cool! I would be really interested to try this with a smaller motor for filament selection to see what we could get away with…
Really excited that this is becoming a thing… Look forward to some updates!
Thanks for the comments everyone!
@Tim_Rastall @Joshua_Rowley l’ll have to see how the weight plays into it, but I don’t think it will be a limiting factor. The Maxstruder that I had previously was a geared stepper motor and was pretty hefty but I still could do 1000 mm/s^2 acceleration without breaking a sweat. I estimate that this whole thing weighs about 0.8 kg. I bet we could drop both steppers down in size significantly and I have some small ones that I’ll try next. The current steppers have 5.5 kg cm holding torque which is overkill based on people who say that you can drive 1.75 mm filament directly with a nema 17.
@Nope_Nope Yeah I’m still trying to figure out the best way to tidy up the cables too. I just lengthened the motor wires a bit which should help. I’d be interested to see any solutions you have, I saw a really cool electronics box by Tim Rastall on his Tantillus but I haven’t designed one for my Rambo Electronics yet. Finding a place for the water cooling tank seems like even more of a challenge! 
@Stephen_Jensen wrt pla resistance. Try ‘Seasoning’ the heat break by dipping a piece of pla in cooking oil, and then push it into the cold break. Remove the oily pla, bring the nozzle up to temperature and then push a new piece of pla through. It will fizz and smoke for a while, in my case there was a strong smell reminiscent of doughnuts. You should notice an immediate improvement. Makes sense as PLA is a starch derivative and starches stick to unseasoned stainless.
Glad to see somebody doing this. The idea has popped up in IRC more than once but nobody ever did anything about it.
Awesome write-up, I enjoyed reading your other blog posts as well
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