N-Headed Multistruder (Plan A)

What is it?
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Its an experiment to see if we can drive a large number of extruders from just two motors and one of the common circuit boards which are only capable of driving at most two motors.
In the SCAD files for this thing you specify the X & Y dimensions of your print bed is and the program works out how many extruders can fit in a housing that will fit on your print bed.
STL files have been included for N=4, other sizes can be generated using SCAD.
Concept
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If you use one motor to select an extruder and the other motor to drive the selected extruder, then you're not limited by number of motors but by how many extruders you can squeeze on to your print bed. Such a mechanism would be way too large to fit on the x-carriage so this is all intended to use bowden tubes to get to the hot-end on the X-carriage.
For this to be entirely useful, it will also be necessary to build a conjoined hot-end. (I've found that most of my ABS varieties print at similar temperat