Poorman's Dual Drive Extruder (BMG clone) for Prusa Mini

I wanted Dual Gear Extruder for my Prusa Mini+ but don't want to break bank for it.

So I bought ~$4 BMG clone hardware from Ali Express and printed case based on available models but non of them fit my needs. I decided to design my own housing remixing Prusa original step files with BMG clone I found on GrabCad web site (big thanks to anderfogel for his work).

The new extruder case is 12mm wider than original with motor rotated 45deg.

Reqirements:

• keep original filament path
• mount on original YZ axis
• reuse as much hardware from old extruder as possible
• make it cheap

BOM:

• 1x BMG clone hardware from Ali Express
• 1x M3x8 screw (from Prusa mini spare parts)
• 1x M3nS square nut (from Prusa Mini spare parts)

BOM (reused from original extruder):

• 1x Bearing 625 2Z
• 4x M3n hex nut
• 1x M3x40 (idler screw without spring)
• 3x M3x25
• 3x M3x12
• PTFE tube 4x2x150 mm
• PTFE tube 4x2x15 mm
• PTFE Fitting MINI

Printed Parts:

• Extruder Front
• Extruder Rear
• Extruder Arm

Print settings (m3f with all settings provided):

• Prusament PETG
• 0.2mm layer height
• 20% grid infill
• manual organic tree paint on support for Rear part

Assembly:

1. Unload old filament
2. Remove and disassemble old extruder (see original Prusa assembly instructions for help)
3. Add 3x M3n hex nuts to front part (I suggest glue them with Super Glue as it will be hard to reach them one motor is in place)
4. Add 1x M3nS square nut for Arm screw
5. Add 625 2Z bearing
6. Add M3x40 screw (must be inserted before motor)
7. Install BMG shaft with filament gear
8. Install motor gear
9. Put front part to motor gear (mount with motor cable facing bottom or front)
10. Screw 2x M3x12 motor screws
11. Add small bearing to BMG shaft
12. Mount Arm to Rear part and add filament M3n hex nut (glue if possible)
13. Add PTFE tube 15mm, PTFE fitting (do not tighten yet as the part can break) and PTFE bude 150mm (secure with M3x12 screw)
14. Secure Rear and Front parts with 3x M3x25 screws
15. Mount on YZ rail using M3x40 and M3x8 screws
16. Fasten PTFE tube fitting (slowly and carefully)
17. Secure cable with zip ties
18. Go to “Settings” → “Hardware” and long press knob on “Hardware” it will open experimental settings
19. Set “Extruder steps per unit” to 415 and “Extruder direction” to “Wrong” than “Save and return”
20. Load new filament and calibrate first layer

It prints perfect (see Benchy in photos). Next I'm considering adding IFS.

Enjoy :)

Full rework of internal structure to fit BMG extruder hardware. Motor position rotated 45deg. Keeps original filament path. Remixed together step files from prusa and grabcad.