DRONES are getting ever smaller. The latest is the first insect-sized robot to take to the air without a tether delivering its power.

To get their device aloft, Sawyer Fuller of the University of Washington, in Seattle, and his colleagues, who will be presenting their work at the International Conference on Robotics and Automation in Brisbane later this month, had to overcome three obstacles. One is that the propellers and rotors used to lift conventional aircraft are not effective at small scales, where the viscosity of air is a problem. A second is that making circuitry and motors light enough for a robot to get airborne is hard. The third is that even the best existing batteries are too heavy to power such devices. Nature’s portable power supply, fat, packs some 20 times more energy per gram than a battery can.

In 2013 Dr Fuller, then at Harvard, was part of a team which overcame the first of these hurdles, making a robotic insect that weighed just 80mg. The team copied nature by equipping their device with a pair of wings which flapped 120 times a second (close to the frequency of a fly’s wing beat). They partly overcame the second hurdle by doing away with conventional motors and driving the wings using a piezoelectric ceramic that flexes in response to electrical currents. The third, however, stumped them. Their drone was powered by means of a thin cable—and this cable also served to send control signals from equipment too heavy to be installed on the drone.

Dr Fuller and his new colleagues have now—almost—cracked the remaining problems. They have made the electronics which flap the wings lighter, by cutting the circuitry from copper foil using a laser, rather than printing the pattern onto a base. They have also added an 8mg solar cell to their device. Focusing a laser on this cell lets them power the robot without wires. They have dubbed their gizmo “RoboFly”.

The caveat is that, because they have not yet developed a way to make the power laser track the drone, as soon as it flies out of the beam it drops unceremoniously to the bench top. Solving this should not, however, be too hard—and once it is done they hope RoboFly will be flapping happily around their laboratory.

After that, it is a question of adding sensors and a communications capability to permit their tiny automaton to be controlled remotely, so that it can actually be used for something. The result, the team think, will be sure to make a buzz.