See this thing in action on:
I wanted to create a filament holder where the extruder wouldn't need to pull the reel to get it's filament deliverd. So i made this motorized version. It's dead simple, two cheap toy motors rotate the wheel when there is enough pull on the filament.
The pull is detected by two microswitches, either one of them switches current to the motors. This way you never have to turn anything on or off. The filament feeder accepts different size of reels without having to adjust bolts and nuts.
Everything is purpose designed in OpenSCAD, with the parameters defined up front, so you can easily modify things yourself if you want to. The drive wheel is a modified version of: http://www.thingiverse.com/thing:883165
The two motors are overkill, either one of them if powerfull enough to drive the reel, but i like the symmetry and they are almost a cheap as the bearing i would otherwise need.
This was really fun to build, i had the idea in my had for a couple of weeks and then saw the challenge, so decided to build it. All parts where designed on the go, so while the build progressed it became clear what was needed. And thanks to 3d-printing it's so easy to create just that part that's needed. The whole thing was build in two days and this first version worked precisely as i imagined.
The filament feeder is build on a wooden platform, because it's easy to build and solid. I used wood from a toy building set i had leftover from my youth (many centuries ago). These a four beams of 25.2x25.2x200 mm, but for the build the size doesn't matter to much.
There is one design for the motor mount, but you have to mirror it in your printer software (i use repetier) to print the second mount.
the rod between the two motors is part of a broomstick, 24mm in diameter, but if you have something different, adapt the OpenSCAD file and regenerate the STL.
You have to saw a cross in both ends of the rod, so it fits the motor-wheels (it's obvious once you have these printed).
The motors are cheap toy motors with reducer from China, e.g. http://bit.ly/1QipvW3
The micro-switches are originally meant for endstops, but the pcb makes them easy to mount: http://bit.ly/1JMtQhV
The rod is standard 4mm and the V-groove bearings also come from China: http://bit.ly/1hNhnkB
I have a electronics wire between the two micro-switches, and the filament behind it. This is wire with Teflon coating (which i happened to have laying around) and the ends are stripped and turned around the levers of the micro-switches, soldered en i bend the levers around that the get a good fix.
The circuit is made op of a power source of 4 AA batteries, then the two micro-switches in parallel and then the two motors in parallel.