Dual motor, dual drive bowden extruder. Uses two NEMA14 motors and two drive gears. The two motors should be wired to run in opposite directions, and can be wired in serial or parallel (I would tend to wire the motors in series on a 24V printer and parallel on the 12V printer, but it will also depend on the motors and drivers).
Two screws are used to adjust the gap between the gears, or small springs* can be used for a constant tension configuration.
Here are the parts I used:
More info about several other dual drive bowden extruders I've just uploaded on thrinter.com
Printed in Atomic Filament Ruby Red PETG*