There is no better way to learn electronics and design than 3D printing and building your own gadgets. If you love astronomy, you may want to give the PiKon Telescope a shot. It is a project that shows you how to build a 3D printed Raspberry Pi powered astronomy camera. The eye-piece of a reflector telescope was replaced with a Pi camera. The telescope mirror takes care of focusing.
The PiKon is built using 3D printing parts, Pi 2, and a bunch of other simple components. You can get the parts for this project here.