Stackable planetary gearbox

layer .2mm
nozzle .3mm
no support needed
reduction per element: 3.75:1, but it may be selected in .scad file
advice: set "seam position" to random
there are 3 clearance definitions in the .scad file:
tol - clearance between gears
dh - vertical clearance of rolls
dd - horizontal

based on http://www.thingiverse.com/thing:53451

added slightly miniaturized version with:
outer diameter of ring: 45
pressure angle: 20
helix_angle: 45

and smaller, with ratio 13:56, pitch 2.5mm
added flywheel for the smallest one (should be printed with 100% infill)


added 40mm version
nozzle .3mm, layer .15mm
clearance set to .43mm, may be lowered on better printers