Simultaneous multiextrusion

Hi community! I need to produce a simultaneous multi-extrusion using Tricolour Mendel 3 running on RepRapFirmware (latest version) the thing is that I got an extruder with duel feed of the filament and I need to create virtual "tools" that would allow me to extrude with 2 motors(at cpecified rates). Any idea how to do it ? There is a solution for Repetier wirmware, they got M163 and M164 codes, that pretty much does what I want, but I dont know if I can run Tricolour Mendel 3 (Duet) on Repetier and it would be preferred to stay with RepRap Firmware. Any ideas ?

See [reprap.org] for how to define a mixing extruder, which is a similar situation. Currently it needs a special form of gcode to drive it e.g. G1 X10 Y10 E5:6 would tell it to extrude 5mm from the first extruder of the current tool and 6mm from the second extruder. But I am already implementing a mechanism in RepRapFirmware for someone else, to allow the mixing ratio to be defined by a separate gcode, so that you would need only a single extrusion value in the gcode file.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].