The Prusa MMU3 for the MK4 3D Printer finally arrived April 2024 and here is my step by step assembly guide with many tips and tricks where I show how to assemble the MMU3 (Idler, Selector, Pully Body, Electronics), upgrade the MK4's Nextruder for the MMU3, and configure the software and firmware for both. I show the new Prusa Buffer and Spools, but then showcase my own custom Multicolor System, and finally print a test model to demonstrate. Prusa Links: Prusa 3D Printers - https://www.prusa3d.com/ MMU3 Assembly Guide - https://help.prusa3d.com/guide/1-introduction_400300 MK4 and MMU3 Firmware - https://help.prusa3d.com/downloads MMU3 Printable Files - https://www.printables.com/model/531604-mmu3-printable-parts Custom Parts Shown: PC4M10 Rear Connection Custom Part: https://www.printables.com/model/542409-mmu3-pc4m10-rear-connector Custom Colored Label Plate: https://www.printables.com/model/542588-mmu3-label-plate-with-custom-colors-mmu Custom Spool and Filament Multicolor System (1:11:25) https://www.printables.com/model/555238-mcs-multi-color-system-for-prusa-mmu3 Alternate Buffer by Martin: https://www.printables.com/model/30811-mmu-slot-buffer PINDA Strain Relief: https://www.printables.com/model/105389-finda-cable-stress-relief 3mm ID PTFE tubes throughout (the short ones in the MMU and behind it to the buffer/spools) https://www.amazon.com/gp/product/B07B8CT1YH My Printables Profile: https://www.printables.com/@Real3DPrints Basic Five Color MMU Test Model by Alloria: https://www.printables.com/model/1568 Chapters Intro: (0:00) Box Contents: (1:00) Self Printed Orange Parts: (1:32) Why Upgrade: (2:05) Where to Get New Parts: (3:49) Idler Body Bearings: (4:54) Idler Body Motor: (9:00) Idler Body Alignment: (12:16) Selector Magnets, Ball, Trapeze: (13:24) Selector Tubes, PTFE Cover: (15:04) Selector SuperPINDA, Cutter: (16:38) Pulley Body Bearings: (19:38) Pulley Body Custom PTFE tubes: (20:21) Pulley Body Front PTFE Holder: (21:29) Pulley Body Rear PTFE Holder: (22:26) Pulley Body Pulleys, Motor: (23:30) Pulley Body Alignment: (26:52) Pulley Body Selector Install: (27:28) Pulley Body Idler Body Install: (31:04) Pully Body Idler Screw Tension: (32:01) Required New Static Protection Parts: (32:59) Pulley Body Control Board, PD Board: (34:05) Pulley Body Cable Connections: (36:07) Pulley Body Cable Management: (38:46) Pulley Body Frame Holders, Label Plate: (40:05) Attach Serial Sticker, Mount MMU3: (42:05) Nextruder Disassembly: (42:48) Nextruder Idler: (44:48) Nextruder Swivel: (46:00) Nextruder Tension Screw: (49:29) Nextruder Gearbox Disassembly: (50:34) Nextruder Main Plate: (51:05) Nextruder Gearbox Assembly: (53:10) Chamfered side faces Nextruder: (53:44) Connect MMU3 Cable to MK4 Electronics Box: (56:29) Update MK4 Firmware: (57:38) Get MMU3 Firmware: (59:07) Turn MMU3 On: (59:46) Update MMU3 Firmware: (1:00:38) Fix Unload Filament Message: (1:01:46) GearBox Alignment: (1:02:40) Filament Sensor Calibration: (1:03:37) SuperFINDA Calibration: (1:04:26) MMU3 New Buffer: (1:06:00) Spoolholder Assembly: (1:07:43) Preloading Filament: (1:09:09) Custom Multicolor System Intro: (1:10:36) Updating Prusaslicer Config: (1:10:52) Custom Multicolor System Benefits: (1:11:25) Fixing Loose Pulley Grub Screws: (1:12:54) Preloading Filament Again: (1:14:05) Printing Five Color Test Print: (1:14:43) Conclusion: (1:16:01)