Mini stepper driven clock

This is a small stepper driven clock mechanism, there is no clock face. The files include some very basic hands, but better to add your own.

I originally tried [this clock](https://www.thingiverse.com/thing:2555644), but wanted to see if I could make something much smaller. This design is 7cm X 6.5cm X 5cm (including the stepper motor.

It uses brass tubing for bearings - sizes from 2mm to 5mm.

In the end I wrote some python code that uses solidpython and scad gears 5.1 to do the heavy work. The base plate is setup for a 28BYJ-48 stepper motor which I converted to bipolar and drive from a Raspberry Pi using a smart drive chip (TMC5130). The stepper drives an intermediate stage bewteen the second hand and the minute hand, so flat out the clock can almost go at 4 hours per minute. At normal speed the stepper gives a slight tick to the movement of the second hand.

[python gearbox code](https://github.com/pootle/gearbox)