Flying robots are among the most challenging domains of robotics, but the achievement of Massachusetts Institute of Technology (MIT) assistant professor Kevin Yufeng Chen and team is exciting news. The researchers have built a new generation of tiny, agile drones, allowing them to operate in cramped spaces and withstand collisions. 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 aerial robots are powered by a new class of soft actuator, which allows them to withstand the physical travails of real-world flight. Chen hopes the robots could one day aid humans by pollinating crops or performing machinery inspections in cramped spaces.
Chen’s work has appeared this month in the journal IEEE Transactions on Robotics. His co-authors include MIT PhD student Zhijian Ren, Harvard University PhD student Siyi Xu, and City University of Hong Kong roboticist Pakpong Chirarattananon. As it is generally known, drones require wide open spaces as they are neither nimble enough to navigate confined spaces nor robust enough to withstand collisions in a crowd. “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 robots that can move around in very complex, cluttered spaces?”
According to Chen, “The challenge of building small aerial robots is immense.” Pint-sized drones require a fundamentally different construction from larger ones. Large drones are usually powered by motors, but motors lose efficiency as you shrink them. So, Chen says, for insect-like robots “you need to look for alternatives.” The principal alternative until now has been employing a small, rigid actuator built from piezoelectric ceramic materials. While piezoelectric ceramics allowed the first generation of tiny robots to take flight, they’re quite fragile. And that is a problem when building a robot to mimic an insect, considering that foraging bumblebees endure a collision about once every second.
Chen has designed a more resilient tiny drone using soft actuators, made of thin rubber cylinders coated in carbon nanotubes. When voltage is applied to the carbon nanotubes, they produce an electrostatic force that squeezes and elongates the rubber cylinder. Repeated elongation and contraction causes the drone’s wings to beat fast. Chen’s actuators can flap nearly 500 times per second, giving the drone insect-like resilience. “You can hit it when it’s flying, and it can recover,” says Chen. “It can also do challenging moves like somersaults in the air.” The drone weighs in at just 0.6gm, approximately the mass of a large bumble bee. Chen is working on a new prototype shaped like a dragonfly.
Building insect-like robots can provide a window into the biology and physics of insect flight, a longstanding avenue of inquiry for researchers. Chen’s work addresses these questions through a kind of reverse engineering. “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.” But Chen aims to do more. His drones can also be useful in industry and agriculture.
Chen says his mini-aerialists could navigate complex machinery to ensure safety and functionality. For example, a drone can move around a turbine engine with a small camera to check for cracks on the turbine plates. Other potential applications include artificial pollination of crops or completing search-and-rescue missions following a disaster. What was science fiction once is now becoming a reality.
