Customizable planetary gearbox

If you want this printed, please visit this link and ask for the special Thingiverse discount:
https://www.3dhubs.com/eindhoven/hubs/cncreate/3dprint

This is a customizer to create your very own planetary gearbox. Keep these principles in mind while choosing your parameters. If you don't, your gearbox will be useless.

R = amount of teeth in the ring
P = amount of teeth in the planets
S = amount of teeth in the sun

Equations
1. ratio = incoming speed / outgoing speed = (R + S) / S => R = (ratio - 1) * S
2. P = (R - S) / 2 = whole number

Use the first equation to determine R and S, do this by fixing the ratio and find the smallest combitination of R and S that fits the second equation. Keep in mind that if R is even, S should also be even, else the second equation will never be satisfied. Another important tip is that when you set the ratio too high, the planets will become to big and the sun will be too small. Also, don't make the amount of teeth on the gears much lower