Motorized yarn winder

Motorized yarn winder to take a loose spool of yarn and wind it into a neat ball. Rotation is driven by a pulley assembly and a DC motor. Works on the principle of nonharmonic rotation of one axis along another angled axis.

This yarn winder is conceptually based on several other designs, but combines all of my favourite features of all of them.

The bobbin is detachable, so just print one for each ball of yarn you want to wind.

Required parts:
- Large bearing (40mm OD, 30mm ID) for the central axis of rotation.
- Small bearing (30mm OD, 20mm ID) for the axis that the bobbin rotates on.
- 3x silicone O-rings, 15-16mm diameter
- 1x switch: bat style, 3mm surface mount
- 1x 9V battery
- hookup wire
- Some kind of heavy ballast: I used brass shot BBs. Coins would work fine too.
- Cotton balls: to pack the ballast into its chamber and keep it from shifting while the machine runs.
- 1x thick rubber band to keep the ballast chamber closed.
- 1x small wood screw