28BYJ-48 Extruder

Inspired lately by different sources (vlogs, kickstarter campains etc.) I tried to design an extruder driven by lightweight and unexpensive stepper motors 28BYJ-48. While one of them is definetly to weak, I aranged two of them to push the filament.

Assembly video on youtube: https://youtu.be/V-Fpiuc5A9Y

BOM:
3d-printed part "ex28byj-by.stl" x2
3d-printed part "ex28byj-fila.stl" x1
stepper motor 28BYJ-48 x2 (apply bipolar hack to drive them with ramps)
screw M3x10 x8
nut M3 x4
screw M5x16 x2
locknut M5 x2
pneumatic pushfit 4mm / M5 thread x1
MK8 Extruder Drive Gear 26 tooth copper 11 x 11 mm x2
tension spring OD 8mm, 14mm x2