Flying robots can safely run into obstacles without greatly inhibiting flight
If you have ever swatted a mosquito away from your face, only to have it return again, you know that insects can be remarkably acrobatic and resilient in flight. With all of its wind gusts, obstacles, and general uncertainty, those traits help them navigate the aerial world. Such traits are also hard to build into flying robots, but Kevin Yufeng Chen, Assistant Professor at MIT has built a system that approaches insects’ agility.
Chen, a member of the Department of Electrical Engineering and Computer Science and the Research Laboratory of Electronics, has developed insect-sized drones with unprecedented dexterity and resilience. The flying robots, also known as aerial robots are powered by a new class of soft actuator, allowing them to withstand the physical travails of real-world flight. The flying robots could one day aid humans by pollinating crops or performing machinery inspections in cramped spaces, Chen hopes.
In the Journal IEEE Transactions on Robotics, Chen’s work has appeared in this month. Zhijian Ren, PhD student at MIT, Siyi Xu, PhD student at MIT and Pakpong Chirarattananon, Roboticist at City University of Hong Kong.
Drones are neither nimble enough to navigate confined spaces nor robust enough to withstand collisions in a crowd, so they require wide open spaces. “If we look at most drones today, they’re usually quite big,” says Chen. “Most of their applications involve flying outdoors. The question is: Can you create insect-scale flying robots that can move around in very complex, cluttered spaces?”
As per Chen, “The challenge of building small flying robots is immense.” A fundamentally different construction is required for pint-sized drones from larger ones. Large drones are usually powered by motors, but motors lose efficiency as you shrink them. So, Chen says, for insect-like flying robots “you need to look for alternatives”.
Built from piezoelectric ceramic materials, the principal alternative until now has been employing a small, rigid actuator. While piezoelectric ceramics allowed the first generation of tiny flying robots to take flight, they are quite fragile. And when you’re building a robot to mimic an insect, that’s the problem, foraging bumblebees endure a collision about once every second.
Instead of hard, fragile ones, Chen designed a more resilient tiny drone using soft actuators. Made of thin rubber cylinders, the soft actuators are coated in carbon nanotubes. An electrostatic force is produced when voltage is applied to the carbon nanotubes. This force squeezes and elongates the rubber cylinder. The drone’s wings beat fast with repeated elongation and contraction.
Giving the drone insect-like resilience, Chen’s actuators can flap nearly 500 times per second. “You can hit it when it’s flying, and it can recover,” says Chen. “It can also do aggressive maneuvers like somersaults in the air”. Approximately the mass of a large bumble bee, it weighs in at just 0.6 grams. Though Chen is working on a new prototype shaped like a dragonfly, the drone looks a bit like a tiny cassette tape with wings.
Farrell Helbling, an assistant professor of electrical and computer engineering at Cornell University, who was not involved in the research, said, “Achieving flight with a centimetre-scale robot is always an impressive feat”. “Because of the soft actuators’ inherent compliance, the flying robots can safely run into obstacles without greatly inhibiting flight. This feature is well-suited for flight in cluttered, dynamic environments and could be very useful for any number of real-world applications”.
Helbling adds that a key step toward those applications will be untethering the flying robots from a wired power source, which is currently required by the actuators’ high operating voltage. “I’m excited to see how the authors will reduce operating voltage so that they may one day be able to achieve untethered flight in real-world environments”.
A window into the biology and physics of insect flight, a longstanding avenue of inquiry for researchers, can be provided by building insect-like flying robots. Through a kind of reverse engineering, Chen’s work addresses these questions. “If you want to learn how insects fly, it is very instructive to build a scale robot model,” he says. “You can perturb a few things and see how it affects the kinematics or how the fluid forces change. That will help you understand how those things fly.” As Chen’s drones can also be useful in industry and agriculture, he aims to do more than add to entomology textbooks.