Overshadowed by their intellectual Arduino superiors are the BEAM robots. These plucky bots are governed by three laws – to extract power from radiation, to recycle and to be simple. Their form derives from their function and circuitry is strictly analogue. They are [probably] the simplest robots about.
British-born robotics physicist Mark Tilden is the brain behind them, designing the first in 1988 after being inspired by a talk by Rodney Brooks about robotic intelligence. It was known as The Solaroller. The clever design incorporated a solar panel, a capacitor and a motor. To save on weight no chassis or PCB was used, instead wire twisted around each other and components bent into appropriate positions.
A solar panel alone is unable to generate enough power for the motor in a design like this, so Mark added a capacitor; a component similar to a battery. The solar panel charges the capacitor and after a few seconds the capacitor forces a belch of electricity into the motor, propelling the whole thing forward.
Since the Solaroller BEAM robots have multiplied and evolved into a range of bizarre creatures. A notable improvement is the incorporation of sensors, letting the robots react to their surroundings. A second motor and LED’s were added to the design. Light Emitting Diodes, when inverted, change function and work similarly to Light Dependent Resistors. With some clever schematic design Mark was able to build a robot which could calculate the direction of the brightest light source and then move towards it, all without a microprocessor.
Sadly support for the bots seems to have dwindled and their parts sold for motor oil, but you can still grab yourself all sorts of BEAM kits at Solarbotics.