update: The brass gears are showing signs of wear after only a few months heavy use (see pictures). I would recommend using the newer version of this design using stainless steel gears. If you use this version, get extra brass gears as they will probably need to be replaced occasionally. Since all the wear happens on one edge of the gear, you can also swap the two brass gears to double the lifespan before replacing them.
Cheap 1.75mm dual drive extruder using standard parts. It uses 4 drive gears, two of them function as gears, keeping the other two drive gears in sync. The secondary gear is tilted to adjust the pressure on the filament. Make sure the set screws don't interfere during assembly, shorter set screws may be needed on some of the drive gears.
More info about how this differs from several other dual drive bowden extruders I've just uploaded on thrinter.com
Printed in Esun Translucent Blue PETG*