jamius.com

Whats a good gear configuration which can convert big speed into big torque, in a compact manner?

My only idea is to use an epicyclic gear, but I have trouble making an annulus.

I can't use a worm gear because I want to convert torque to speed, not the other way around.

Can you make some planetary gears? ...or does it need to be more compact?

This is a good way to get what you want.
http://www.youtube.com/watch?v=cnJCWX2nr4M

I don't know what you have the ability to make, but with the hypocycloidal gear reduction you can dial in a ton of reduction without adding extra length do to gearing down in stages like a lot of gear reductions would need you to do. It also has the benefit of being nearly backlash free.