This is really a simple design. The only complication was the hinge: we had to come up with an idea which is easy to print, easy to assemble and still reliable. We tried several ideas, and in the end, this five part version was the best. You can read more about it on our website. It has been written in JavaSCAD, so you need a bit of a Java knowledge to modify the parameters. I uploaded a simple example for those who want to see the result before download the source code.