"Eggbot redrawn" modifications

I've slightly modified the drive cup and idler cup from [thing:844167](https://www.thingiverse.com/thing:844167). I'm posting this in case it's useful to someone else.

I've made the following changes: the drive cup has been modified to fit exactly the shape of the stepper motor axis, and the inner diameter of the idler cup has been increased slightly.

drive_cup.stl and idler_cup.stl are the original files from [jsc](https://www.thingiverse.com/jsc/about). My changes are parametric, you can check the OpenSCAD files or directly print *_modified.stl.