Researchers at Northwestern University, Illinois, USA, have created what could be called the world's smallest remote-controlled walking robot. These tiny, crab-shaped robots, which are only half a millimetre in size, can walk, crawl, turn and even bounce without using any electrical or hydraulic components.
What enables these tiny robots to move is a shape memory alloy. Heating such alloys causes them to return to their original shape, having previously been bent or deformed in any way. The role of the spring that deforms the cold alloy is a thin layer of special elastic glass on top.
The heat, which causes the alloy to heat up, is supplied by a beam of laser light. Since the robots are very small, the heat propagates quite quickly through their "body", enabling a high contraction rate, which can reach up to 10 cycles per second. The focus point of the laser beam determines the direction of movement, while more complex movements of the laser beam cause the robot to perform complex movements, including on-the-spot turns, jumps, etc. By reducing or increasing the intensity, by adjusting the modulation of the laser light, it is possible to control the speed of movement and movement, which at its maximum is half the length of the robot's body per second.
The process of manufacturing such tiny mechanisms is done in several stages. First, the entire robot structure is formed flat, which corresponds to the initial shape that the robot will tend to take when heated. This flat structure is placed on a rubber base evenly stretched in all directions, the contraction of which causes the legs to deform and bend, corresponding to a deformed "cold" state. A glass layer is then applied to the surface, which will act as a spring once it has hardened.
Of course, one such tiny robot is unlikely to be able to do any meaningful amount of useful work, and controlling a large group of such robots is a very difficult task because each robot requires a separate laser with individual control. Nevertheless, "the combinations of materials and assembly techniques we have developed will make walking robots of all shapes and sizes possible," the researchers write, "and it is possible that next generations of robots will already be able to do some useful work.