Also, if you want a super cool robotics idea, I recommend building a prusa 3d printer (https://www.reprap.org/wiki/Prusa_Mendel).
- Plans are available online
- Components are 90% obtainable through your local hardware store
- Other 10% is the extruder and parts you need another 3d printer to print
Raspberry Pi is a typical microcontroller for Prusa 3d printers.