[OLD] COBRA System for Original Prusa Enclosure

🆕 UPDATE 12 March 2025

Check out my new spool-solution - the BUFFER UNIT! This is a way different setup from the COBRA-edition. It features and integrated, gravity-powered filament rewind mechanism inside the spool holder itself. The spools sit on rollers, so the loading procedure is a breeze - no tedious loading procedures, just push the filament to the MMU. This creates a very compact setup - this opposed to the usually large and clunky setup required to run the MMU. 

→ Check out the BUFFER UNIT by clicking here. 

(OLD) COBRA System for Original Prusa Enclosure

A fully complete solution for the MMU with the Original Prusa Enclosure: all five spools fit inside the enclosure including a new easy-to-use buffer. Switch from loading and buffing filament with a simple flick of a lever.

HOW TO LOAD

1. Flick the lever to the loading position and 
2. Insert the filament through the PTFE-tube until it reaches the MMU. Make sure the MMU is loading the filament. 
3. Flick the lever to the buffer position. Done!

HOW TO UNLOAD

1. Just pull the filament out, regardless of lever position. Done!

General information

The COBRA system is comprised of a buffer, spool holders and PTFE guides. Four spools fit at the front of the enclosure, one print-in-place retractable spool holder at the back. This is to accommodate 1 Kg spools, something that all spool holders in the COBRA system supports. 

Each spool holder has its own respective filament guide, each numbered with the corresponding MMU-filament. The filament goes to the buffer via PTFE-tubes, where it's routed through the Buffer-wheel and -slider. There is in other words no need to manually route the filament by hand, just push the filament and the COBRA buffer will do the rest for you (granted that the switch is in the loading position). Flipping the lever to the buffer position moves the slider, allowing for downwards movement of the filament. The filament can thus be buffered. 

The Spools at the front largely block the light from the official Prusa White LED Strip for Original Prusa Enclosure. It's possible to flip the Strip sideways in order to improve the lighting. All other official Prusa addons are fully supported with the COBRA system. 

Inside the 1.0.0 Beta version of the COBRA Buffer

Materials

• PC4-M10 PTFE Connector (10x)
• 8x22x7 Bearing included with the MMU2/MMU3 (5x) 
• 2mm ID, 4mm OD PTFE Tube
• M3x12 screw (10x)
• M3x8 screw (17x)
• M3x4 screw (9x)
• M3n nut (32x)

Print instructions

Default settings (see exceptions further down)

• 0.2mm layer height
• 20% infill
• Enable bridging
• Disable supports

Buffer-wheel

• 0.1mm layer height

Buffer-main-body

• Add detail using the Variable layer height function according to the picture below. 

• Paint a seam in a straight line through the middle of the part using the Seam painting feature in PrusaSlicer.

Buffer-slider

• 0.1mm layer height
• Place a seam on the groove at the back of the part

Buffer-switch (optional)

• Use multimaterial printing for the numbers 

Tools

• 2.5mm hex key
• 10mm Wrench (or Pliers)
• PTFE Tube Cutter (recommended)
• Drill bit for PTFE Tube chamfering
• Flat head screwdriver

❗Before proceeding with the assembly, please install the official Hinged lid for adding MMU to Original Prusa Enclosure. This vastly improves spool accessibility and ease of assembly. 

Assembly Instructions 

Step 1 Filamentguide part preparation 

• Guide-1 (1x)
• Guide-2 (1x)
• Guide-3 (1x)
• Guide-4 (1x) 
• Guide-5 (1x)
• Side-guide (1x)
• Top-guide-A (1x)
• Top-guide-B (1x)
• Temperature sensor (1x)
• M3x4 (5x)
• M3n nut (17x)

Step 2 Filamentguide (1/15)

• Insert 3 M3n nuts in the Side-guide and Guide-5. Use the “screw-pull-method” for proper insertion. 

Step 3 Filamentguide (2/15)

• Insert 2 M3n nuts in the Top-guide-A and Top-guide G. Continue to use the screw pulling method for proper insertion. 

Step 4 Filamentguide (3/15)

• Insert 6 M3n nuts in the Guide-1 and Guide-4. 

Step 5 Filamentguide (4/15)

• Insert 6 M3n nuts in the Guide-2 and Guide-3. 

Step 6 Filamentguide (5/15)

• Insert the M3x4 scews into the Guides-1,2,3,4,5. Turn the screw until it catches the nut on the other side. We will fully tighten these screws later on. 
• If you're having trouble catching the nut, try pressing the nut with your finger while turning the screw. 

Step 7 Filamentguide (6/15)

• Insert the temperature sensor inside Guide-3. Press with both fingers till it snaps into place. Make sure the sensor is in the right orientation, see picture. 

Step 8 Filamentguide screw preparation (7/15)

• M3x8 screw (12x)

Step 9 Filamentguide (8/15)

• Align the holes of the Guide-4 with the ones on the front-left side of the enclosure. Pay attention to the notch in the picture. 
• Tighten the Guide-4 into place with two M3x8 screws. 

Step 10 Filamentguide (9/15)

• On the other side of the enclosure to the right, attach Gude-1 with two M3x8 screws.

Step 11 Filamentguide (10/15)

• Align the holes on the Guide-3 with the ones on the front-left top corner of the enclosure.
• Secure it with two M3x8 screws.  

Step 12 Filamentguide (11/15)

• Again, repeat the previous step with Guide-2 on the opposite side of the enclosure to the right. 

Step 13 Filamentguide (12/15)

• Now, align the Guide-5 on the top of the enclosure, where the printed arrow is facing towards the front of the enclosure. 
• Secure it in place with a M3x8 screw

Step 14 Filamentguide (13/15)

• Yet again, repeat the previous process for the Side-guide on the opposite side of the enclosure. 

Step 15 Filamentguide (14/15)

• Align the hole on the Top-guide-A with the one on the enclosure. The Top-guide-A is mounted next to the Guide-2. 
• Secure the part with a single M3x8 screw on the other side. 

Step 16 Filamentguide (15/15)

• Finally, repeat the last step now with the Top-guide-B

Step 17 Spool holder part preparation

• Spool-holder-1 (1x)
• Spool-holder-2 (1x)
• Spool-holder-3 (1x)
• Spool-holder-4 (1x)
• Spool-holder-5 (1x)
• M3x12 screw (10x)
• M3n nut (10x)

Step 18 Spool holder (1/6)

• Insert the 10 M3n nuts into the 5 Spool-holders. Pull the nuts with a screw. 

Step 19 Spool holder (2/6)

• Align the holes on the Spool-holder-1 with the ones on the enclosure. The Spool holder is located near the Guide-1. 
• Attach the Spool-holder-1 with two M3x12 screws on the other side of the printer. 

Step 20 Spool holder (3/6)

• Above the previous spool holder, secure the Spool-holder-2 with two M3x12 screws. 

Step 21 Spool holder (4/6)

• On the other side of the enclosure next to Guide-3, attach the Spool-holder-3 with two M3x12 screws. 

Step 22 Spool holder (5/6)

• Under the previous holder, secure the Spool-holder-4 with two M3x12 screw

Step 23 Spool holder (6/6)

• Finally, attach the Spool-holder-5 with two M3x12 screws at the back of the printer. Note the hexagon cutout on the back acrylic glass. 

❗1.1.0 Buffer instructions are in draft phase at the moment. You can find 1.0 instructions under files❗

Step 27 Buffer (1/13)

• Insert two M3n nuts through the slots at the top of the Buffer-main.

Step 27 Buffer (1/13)

• Lay the Buffer-main on its side according to the picture. 
• Align the Buffer-lock with the Buffer-main and slide it all the way down. 

Step 27 Buffer (1/13)

• Test the 3D-printed joints of the Buffer-slider by moving them. They should move freely.  
• Position the Buffer-slider according to the picture.

Step 27 Buffer (1/13)

❗This is the hardest step of the assembly, read and look at all pictures before proceeding❗

• Align the grooves on the Buffer-slider with the one on the Buffer-main. 
• Slide the Buffer-slider down as far as you can. Confirm that it moves smoothly.
• Check if the Buffer-slider touches the 45 degree angled slope of the Buffer-main, see picture. If it doesn't touch the right slope, try another groove until you it does.

Step 27 Buffer (1/13)

• Now, rest the Buffer-slider on the Buffer-lock by flipping it. See picture. 

Step 27 Buffer (1/13)

• Locate the pin on the Buffer-switch-5, it needs to be inserted inside the Buffer-slider's slot. 
• Insert the switch through Buffer-lock's one pin. 

Step 27 Buffer (1/13)

• Above the Buffer-lock, slide the Buffer-wheel according to the picture. 
• Align the wheel with the hole on he middle. 

Step 27 Buffer (1/13)

• Insert a Buffer-screw inside the Buffer-wheel. 
• Screw it in place with a flat head screwdriver. 

Step 27 Buffer (1/13)

• Lastly, slide another Buffer-lock on top of the previous one. 

Step 27 Buffer (1/13)

• Insert three M3n in the Buffer-side.