Light-weight and flying robots the size of microscopic insects might have very useful real-world uses, for instance helping search & rescue operations, inspections of dangerous places, and perhaps space exploration. Despite its promise, the reality of these robots has so far been challenging, notably owing to technological challenges faced while attempting to steady their flight and mechanically imitate the intrinsic hovering characteristics of insects.
Researchers at the University of Washington have recently created a flight control and wind sensing system that might assist to handle this hard robotics challenge, eventually allowing the steady flying of robots even as tiny as a gnat. This approach, presented in Science Robotics, is based on the use of accelerometers, a sensor that can detect the acceleration of any moving equipment, object or human.
“For over 40 years, roboticists and microfabrication specialists have been fantasising of producing ‘gnat-sized’ robots only a few milligrammes in weight—first envisioned by Anita Flynn at Berkeley,” Sawyer Fuller, one of the researchers who carried out the work, told TechXplore.
“She and Rodney Brooks subsequently produced the amusing study, ‘Fast, cheap, and out of control: a robot invasion of the solar system,’ that suggested sending small robots out to investigate the solar system, also known as ‘smart dust.’ Such robots would be far smaller than the 100-mg, bumblebee-sized robot dubbed the UW Robofly, which students in my lab have constructed so far.”
In recent years, numerous roboticists worldwide have been striving to design actuation systems for insect-sized robots weighing 10 mg or less and several succeeded, including researchers at Berkeley University and the Army Research Labs. Reliably stabilising and regulating the flight of these exceedingly tiny robots, however, has thus far proven to be troublesome.
“As a general, tiny flapping-wing robots and drones are unstable without feedback control,” Fuller stated. “If you turn on the wings or rotors, they swiftly drop out of the sky. Flies are supposed to compensate by utilising gyroscopic halteres as feedback. So, a simple solution would be to incorporate a gyroscope to the robot design.”
While the inclusion of gyroscopes might potentially assist to overcome technical challenges related with the flight of tiny flying robots, the gyroscopes available today are nowhere near as light or efficient as they would need to be to fly on such light machines. The lightest gyroscope built to date weights 15mg, which is 5mg more than the weight of a complete gnat-sized robot.
“Our suggested answer to this challenge stemmed from my Ph.D. dissertation, where I observed that flies employ a sensation of wind from their feather-shaped antennae to guide their flying,” Fuller stated. “We proved in this work that you can accomplish what flies do, detect airspeed, using a different form of sensor, an accelerometer. The primary advantage is that accelerometers are intrinsically considerably smaller and more efficient than gyroscopes. They are accessible off-the-shelf in a packet weighing only 2 mg.”
In addition to being significantly lighter than gyroscopes, when coupled with excellent models of robot dynamics, accelerometers may also aid to predict the in-flight tilt angle of robots. In their invention, Fuller and his colleagues also integrated an equally light optic flow sensor, and a small computer, to help determine a robot’s altitude and the intensity of the wind.
“When we compared a simulated reaction of our system to a gust of wind with how fruit flies reacted to the same gust, we discovered that the two systems responded pretty similarly,” Fuller said. “So now we have an intriguing idea regarding insect flight control to test. Namely, that flying insects that do not have gyroscopes, like bees and moths, could be able to regulate their unstable flight dynamics by detecting wind with their antennae. “
Fuller and his colleagues evaluated their system in both simulations and real-world trials using a 30-gram robot and discovered that it could effectively stabilise its flight, enabling it to emulate the flight dynamics of fruit flies. In the future, they anticipate that it will be implemented and tested on many different flying robots, including lighter robots weighing 10 mg or less.
“We were able to design a stabilising flight control system based on off-the-shelf hardware that is tiny enough for a gnat-sized robot,” Fuller noted. “Our method might potentially be modified for bigger robots, such as the 100 mg UW Robofly, enabling more cargo to be allocated to a larger battery or additional sensors. In our future investigations, we intend to show it flying on the UW Robofly.”
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