Designed to mount on top of a printer enclosure or a shelf and automatically keep filament supplied to the extruder. For a non-motorized version just make two plain rollers. For automatic use, make a plain roller and a motorized roller. Attach a 37mm 30 RPM 12VDC motor and a 5K 1/4" potentiometer with a long shaft. Use either a simple PWM controller or an Arduino with a motor shield. Some sample code is included and you should customize it to your particular machine. An alarm can be added to shut down the printer in case of a spool jam. I don't have to worry about my spool tangling anymore and my extruder doesn't have to pull as hard to get filament. It takes very little pressure to move the feeder arm.