Does Marlin support 4 extruders (or more)?
If not, who do I have to bribe with a quad-nozzle hotend to get this to happen?
From a hardware perspective, I intend to run RAMPS with a daughter-board off the aux-ports, where there is plenty of digital output for stepper/heater drivers and analogue inputs for thermistors.
Standard build only goes up to E2. What are you doing about electronics? RUMBA only has 3 on board.
Ah, didn’t see that comment.
I think I’ll look into using the expansion interface on t he RUMBA for E3
The 3 extruders limit seems in place in steppers.h/cpp and would obviously require a little extra pin mapping in pins.h.
The code in steppers.h looks like it can be just copypasted to gain the fourth extruder.
Ultimately though I think the way forward isn’t to have 1x stepper+driver per extruder, but to have one driving motor, and a way to switch which filament is being driven. This can certainly be done with just 2x steppers/drivers. Maybe just with 1x stepper and a hobby servo.
That’s my next E3D project after Kraken and E3D-v6 I reckon!
It doesn’t. 
I’ve got 3 stepper drivers working off of a single stepper driver header, and want to be able to go arbitrarily high, but even at 3, Marlin starts disabling the bed temp control, etc.
I was hoping to use a single heater block with 2 heaters, 2 thermistors, 1 bed heater, 1 bed thermistor, and 9 nozzles… 3-bit color printing with FDM. But I’m far too unexperienced to start modifying the firmware to support 9 nozzles. =D
Yeah, I had a quick dredge through Marlin and adding another extruder appears to be non trivial. I forgot you need an extra Thermistor and HE output but the RUMBA actually has this covered up to 4 as long as you don’t want a heated enclosure too. Repetier also appears to only do 3.
We are back from the MakerFaireRome and after a complete day at the Faire and a six hour trip from Rome to home probably I’m very tired and probably do not have a totally clear mind, but I say that I’m very interested in developing and adopting the kraken :-). From a software point of view I’m not so skilled to modify the firmware, but I can start thinking about a custom interface board for the arduino mega to support the 4 extruders 
From a hardware perspective, I think we are fine, even just off a RAMPS board. The AUX ports have digital and analogue pins a plenty waiting to be used.
We need:
1x PWM out pin to drive the 4th hotend MOSFET.
1x Analog In to sense the 4th hotend thermistor.
3x Plain Digital Out to drive the stepper driver (STEP/DIR/ENABLE)
We probably want also:
1x Addtional PWM out pin to drive the bed MOSFET (we used all the onboard FETs for hotends already)
1x Additional Analog In to sense the bed thermistor (we used all the existing temp input headers for hotends already)
This, and piles more, are available off the AUX ports of RAMPS, and RAMBO/RUMBA/MEGATronics for that matter.
@Tim_Rastall
Not really something that i’d considered, but its certainly possible and the I/O exists.
@Sanjay_Mortimer , I’ve been stacking drivers recently. No reason not to share the step/dir pins among drivers is my reasoning. Or maybe at least the dir pin if you wanted to enable ‘holding’ of the motor. I’ve been using the enable line in order to select which motor I want, and setting step/dir of each stepper to be shared, and then stacking the drivers. It actually works, and with a prime pillar I could go way up in extruder numbers without using much more I/O. That’s what I’ve been working on lately. That, and a peachy-printer-alike – still waiting on my laser. =D
Our printrboard + extrudrboard support 3 hotends. Available and working now.
@Brook_Drumm extrudrboard looks like a lovely neat way to add extra FETs and drivers to an existing setup. Is the design open source or is there any deeper documentation I can use to determine if I can hack it into a ramps or similar? I’ve no intention of making clone boards, I would just like to use your board until I can get a more RAMPS/generic solution designed.
Hope your career move to printrbot is working out nicely for you!
@ThantiK You wouldn’t want to be mixing step/dir for the different nozzles if they were different sizes.
Also to clarify what you’re saying because it took me a few reads: You want to just use the ENA pin to control which nozzle is running?
This brings up a question I’ve been holding onto about polulus: Do they have any memory of position when you turn off the enable pin? Or do they just go back to whatever position they count as first each time?
@Nick_Parker I’m not sure I understand how step/dir and nozzle size are related, or why this would cause any issue?
Pololus don’t have any memory of anything whatsoever, they don’t count steps or absolute position, they simply send current to the motors to produce a holding torque or a step as appropriate.
Nope, they don’t have any memory, but who cares? Usually when doing dual extrusion stuff you can just use a prime pillar, or something of similar nature. No reason to worry about the filament slipping backwards, as you’ve gotta pull it quite a ways back anyways, and I’m pretty sure a missed step isn’t going to be the end of the world.
And it doesn’t matter if the nozzles are different sizes or anything of that matter, the slicer takes care of how many steps need to be taken, and since the other extruders aren’t enabled anyways, they don’t care.
I’m honestly picturing a 3x3 nozzle arrangement, with 2 long heater carts running between them, and 2 thermistors placed in the remaining gaps opposite sides of the block. I’ve still got testing to do with 3 nozzles, but I have no doubts that it will work just fine.
Hmm dunno why I thought there would be more than one running at night… Anyway that sounds pretty slick. It would be an awful lot of motors though.