Drosophila robotica is my name for this amazing miniature flying robot created at the Wyss Institute for Biologically Inspired Engineering at Harvard. It's an 80-milligram, insect-scale, flapping-wing robot modeled loosely on the morphology of flies.
Simply scaling down mechanics that work for flight on larger objects wouldn't do. Scaling things down just results in too little force, or it creates a situation where surface interactions between the parts inhibit flight, as things like friction begin to dominate. Rather than taking the traditional route to get something tiny aloft—attaching it to some form of rotary engine—they returned to the fly for inspiration, making a pair of flapping wings.
On the fly, the wings work because the angle they take when moving upwards is different from the one they take when flapping down. The authors set that up so it happened passively; as the wings swept in opposite directions, the hardware at the joint where they met the robot's body forced them to rotate.
To get the wings to beat fast enough, the authors created two "muscles" made from a piezoelectric material, which changes shape when a voltage is applied. These flapped the wings at 120 beats a second. Not only is this rate similar to a fly's, but it also created a resonance in the robot's body that amplified the force of each beat. That resonant frequency was so important that the flight control system never changed it, even when it needed to change the force generated by the wing (to fly up or drop lower, for example). Instead, the force was controlled by changing how far the wing traveled with each beat.
That same approach allowed the researchers to rotate their robot while in flight. By having the left or right side do a stronger beat, the robot would turn.
(Flying robots as tiny as flies)
I'll never forget coming across the amazing Scarab flying insect robot in a 1936 issue of Astounding Stories magazine. Raymond Z. Gallun was one of the three most famous authors of the Golden Age of science fiction (or scientifiction); he's fun to read even today.
The Scarab rubbed its hind legs together, as flies will do when at rest. Then, apparently satisfied that it was in condition, it unfolded the coleoptera-like plates over its wings. With a buzz that any uninformed person would have mistaken for that of a beetle, it started out on its journey.
(Read more about the scarab flying insect robot)