One piece elastic band powered extruder,

thingiverse

This minimalist one-piece extruder drive utilizes elastic bands for tension. Printed at 100% infill with three walls and a 0.5mm nozzle, it's designed for a 8mm x 22mm x 7mm bearing (ID: 8mm, OD: 22mm, thickness: 7mm) that is also known as 608-2Z ball bearing. In version 2, the designer plans to reduce walls to two due to SLIC3R's fill optimization. Additionally, a serrated shaft adaptor from Technobots (http://www.technobotsonline.com/universal-coupling-insert-5mm.html) is incorporated. Version 2 also features a second pair of 'lugs' for adjustable pull force and a shamfered edge to prevent elastic bands from slipping off. The designer has left enough space for a potential 4mm pneumatic fitting. Remember, the flat side (printbed) should be uppermost in assembly, and photos are provided for illustration purposes only. Enjoy! - Ceri