This is a filament winder to go with a home extruder like the Filastruder. The filament drops into a loop and comes back up to the winder. At the bottom are a pair of photo resistors and a laser which monitor the position of the loop and speed up or slow down the winder so it stays in sync with the extruder. The filament is pulled up with a pinch roller based on the Minimalistic Extruder, then runs over a spring loaded arm.
The arm is mounted on a potentiometer, and its position depends on how tight the spool is pulling the filament. Using the reading of the potentiometer, the spool speeds up or slows down as needed to maintain the arm's position, and therefore tension.
On the way to the spool, the filament passes through a guide arm which is attached to a servo. Hall effect sensors detect the rotation of the spool and move the guide over the space of 1 filament diameter so the filament gets coiled evenly across the spool.
The spool mount is a PVC pipe with bearings inside supported on a threaded rod, with a gear on the end. The spool itself is made from 2 printed ends fitted into a 2" PVC pipe, so it would be easy to make spools as needed. The spool simply slides onto the mount and mates with some bolts sticking out of the side of the gear.
The winder is powered by an Arduino Uno with a half breadboard, mounted in this bracket - http://www.thingiverse.com/thing:32838. Eventually I want to replace the breadboard with a custom shield.
Here are some videos of the winder at various stages-
The instructions are too involved for Thingiverse, so I am posting them at my blog, starting with http://wp.me/p2BWKW-9q. Most of the files are here, and are mostly current, but a couple still need to change and be added. I don't have a detailed BOM down to size and quantity of the bolts, but there should be enough there to get you started. I will host the files here and update them, and keep posting about the build at the blog. Files and instructions are works in progress so I recommend following both.