Sometimes when your building a robot you will need gears. Although there are plenty of ready made gearboxes on the market they will not always fit your needs. I have been looking at puting together a collection of gears, shafts and even small bearings so that you can build you own gearboxs.
I started off with the green bevel gears shown below, they have big, strong, chunky teeth that are hard to break. These allow you to have a 90° output.