Gearbox Demo (Solid Core Compound Planetary)

Another demo of the [Solid Compound Planetary Gearbox](https://www.thingiverse.com/thing:3511382) with updated source, tidying up and refining the geometry. SCAD is still an unreadable mess, but a slightly improved. Incorporating clamping jaws and knob options.

Print in place, fully assembled, no supports. Just be sure to have your tolerances dialed in and your slicer preserves the one-layer gap in the outer ring gears. After printing, separate ring gears with something sharp like a spatula or razor blade.