For this workshop I gave Transition Year students at Science Gallery a few basic components - batteries, wires, motors, propellers, LEDs - and a range of recycled and low cost materials - tinfoil, cardboard, pipe cleaners etc - and challenged them to design robots. They had to be functional in some way, be it moving, lighting up, or something else.
My favourite group used a speaker they had made in a soldering workshop we did the previous day, and created 'Hazel the robot', a robot head with light up eyes and a permanently surprised expression thanks to her mouth being a speaker.