This project is an ongoing effort, and you can help. The design files for many different prototypes are available here for anyone to use and improve on.
The aluminum prototypes require machine shop tools to build, such as a shear, brake, and drill press. The plastic prototypes use a laser cutter. You may be able to access these tools at a local hackerspace, a facility such as TechShop, or by using an online or local machine shop.
Cardboard is all you need to begin experimenting, though. This was the very first prototype: