Fly-Like Micro-Scale "Gnat-Robots" Can Stabilize Their Flight with Tiny Sensors

A team of researchers has taken inspiration from nature to drop the gyroscope from flying robots, developing a combination camera and accelerometer replacement, which could scale down to robots weighing just 10mg.

"This article was motivated by recent advances by groups around the world that are creating really small ~10mg flapping-wing devices, about the mass of a grain of rice," first author Sawyer Fuller, assistant professor at the University of Washington, explains. "We wanted to know if we could design a flight controller for a robot that small. Its mass and power constraints would be much more stringent than even the 100mg UW Robofly, or the smallest drone yet to fly itself."

To do so, the team would have to ditch one of the key components of such a device: the rate gyroscope. "Conventional wisdom says that a rate gyroscope, which measures angular velocity, is an essential part of a flight control system. Our solution turns this notion on its head," Fuller explains, "eliminating the gyroscope entirely because it is too heavy and power-hungry (>15mg, >1mW). Instead we used only an accelerometer, which is commercially available in packages weighing as little as 2 mg and 20 microwatts! We combine this with a tiny optic flow camera, which can be made similarly efficient and light, to estimate and control lateral velocity and attitude, as well as estimate wind!"

The team's approach was inspired by nature — specifically the wind-vision sensory fusion fond in Drosophila melanogaster, the fruit fly. By combining data from the accelerometer, which enjoys reduced noise owing to an increased ratio of aerodynamic drag to the robot's mass, and vision input from the camera, the team was able to stabilize a tiny robot helicopter — albeit one weighing 30g, though with experimentation and simulation suggesting that the technology is compact and efficient enough for ~10mg flying vehicles too.

The idea of using nature-inspired wind-vision to ditch power-hungry and heavy hardware recently occurred to a team at the Delft University of Technology and Aix-Marseille University too: back in October, a team published a paper detailing how optical flow vision processing inspired by flies could remove the need for an accelerometer at all.

"Compared to [the] recent article in Nature by de Croon et al," Fuller notes, "we keep the optic flow camera, but add in [the] tiny 2mg accelerometer to give us the ability to also estimate wind. This is really useful for tiny robots as they navigate wind currents or map air flow patterns."

"Small flying robotic insects will revolutionize low-altitude atmospheric 'air telemetry' — remote sensing of air composition and flow — by doing so on a much more detailed and persistent basis than is possible now," Fuller claims. "They will power themselves from the sun or indoor lighting — which favors small scale. Applications include early detection of forest fires, pest onset in agriculture, buried explosives, or mapping hazardous volatiles to find leaks of greenhouse gasses or the spread of airborne diseases."

The team's work has been published under closed-access terms in the journal Science Robotics.