Prusa MMU2S Modification for 12 Filaments

Overview

This is the result of several months of designing and testing new ideas for increasing the filament count of the Prusa MMU2S. I tried several variations, but ended up coming back to something that is largely based on the original Prusa model. Some of the major adjustments include:

increased filament count from 5 to 12
reversed position of pulley and idler motors, to maximize the use of the 110mm pulley shaft
moved FINDA to the rear of the selector, in an attempt to minimize issues where the filament clears the ball but then still fails to fully retract
added quick-release for FINDA sensor, for ability to clean or check ball chamber without re-calibration of FINDA height
selector has integrated threads for PTFE quick-connect
moved control board beneath the body (inspiration thanks to univeraljoint)
additional bracket mounting options
optional integrated OLED display for more detailed state information and enhanced error recovery
selector does not include the cutter

The Disclaimer

These items and related code are provided as-is, with no warranty -- express or implied -- and I cannot personally guarantee that it will function and/or not break your printer. Nothing here, of course, is officially endorsed or supported by Prusa.

That being said, I have had a great deal of luck using this model, or I wouldn't be sharing it.

Software & Firmware

In order to use this model of the MMU, you will need to use the following modified firmware for the MMU board. This has been branched from version 1.0.6, but has numerous significant changes, so whether or not I will keep this up-to-date with future version is questionable.

https://github.com/cjbaar/MM-control-01

In addition, you will need to change the firmware on the printer itself, because the existing code will ignore any tool changes above T4. This is now based on branch 3.11.0. There is a compiled version for the MK3S in the firmware folder of this repo.

https://github.com/cjbaar/Prusa-Firmware/tree/MK3_3.11.0

Finally, in order to create the gcode files, you will need to create a new printer model in a MMU-aware slicer that is setup for 12 filaments. I had no issues doing this in PrusaSlicer version 2.1.0+.

Hardware

Printed Parts

Print one of each included STL file, with the following exceptions:

choose either m6 or m10 thread for selector base
- or original m5 heat-set remix, thanks to obe
choose bracket type (traditional frame mount or table-top)
print four copies of idler-rings.stl
screen is optional, if using OLED display
wrench is optional, but assists with assembling the inlet manifold

I printed all parts with relatively slow speed and 0.2mm layers. I also printed most everything with PLA -- in particular, the selector and idler rings -- because I get better consistency and tolerances for bearings and general fit. In my experience, printing the same model in PETG may make some pieces harder to fit together.

For the "lower" model, there is a related mod file, which I recommended printing with 100% infill. The selector cap might also need to be 100% infill.

Additional Parts

The following pieces are required for assembly. Items in italics may not be included in the original Prusa MMU2, but should be easily found on Amazon (or your world domination retailer of choice).