Re: How many extruders do you need?

Just a thought - why not multiplex the extruder control and switch on whichever extruder you require (you could feasibly do it with one extruder driver and just multiplex the output control with a couple of mosfets per channel) and use I2C to switch on/off the channel you want to drive. It could allow for relatively easy switching of multiple extruders. If you want to mix several colours at once, then a mix chamber before extrusion is probably the easiest way (spiral grooves? Mixing impeller?) with a single heat source and four bowden tubes to feed it? So then your temp control doesn't expand as your only driving one extrusion nozzle, but the control only needs to expand to multiple feeds into the nozzle

Just a thought