Rotor: Filament Encoder

Rotary filament encoder.

Features internal filament guide.

Customize model with [OnShape](https://cad.onshape.com/documents/3854caedf5324700f09af4d0/w/8bc8c94a59071f26e7e23244/e/0b69ac1635183760dce412f5).

Example usage with [SmoothieBoard](http://smoothieware.org/filament-detector).

Parts:
* 1 x [HC-020K sensor](https://www.aliexpress.com/wholesale?SearchText=HC-020K)
* 3 x [625ZZ bearing](https://www.aliexpress.com/w/wholesale-625zz.html)
* 2 x [PC4-M6 socket](https://www.aliexpress.com/wholesale?SearchText=pc4-m6)
* 1 x [5x11(4+7)mm(40T) gear](https://www.aliexpress.com/item/10Pcs-3D-printer-Accessories-40-Tooth-40-Teeth-Gear-Inner-Diameter-5MM-For-Makerbot-Reprap-Extruder/32819947240.html)
* 1 x [JST 3-pin connector](https://www.aliexpress.com/wholesale?SearchText=jst+xh+3+pin+male)
* 1 x [0.7x4.5x14mm spring](http://www.homedepot.com/p/Everbilt-Spring-Assortment-Kit-84-Pack-13554/203133714)
* 4 x [3.5x25mm screw](http://www.homedepot.com/p/Grip-Rite-6-x-1-in-Phil