Drones in the Daffodils
By Wyss Institute
TAKING THEIR CUES FROM THE BIOLOGY of a bee, researchers at the The Wyss Institute for Biologically Inspired Engineering at Harvard University, Boston, are developing RoboBees, man-made systems that they say could perform myriad roles in agriculture or disaster relief. A RoboBee measures about half the size of a paper clip, weighs less that one-tenth of a gram, and flies using “artificial muscles” created with materials that contract when a voltage is applied.
The masterminding of the RoboBee was motivated by the need for autonomous micro-aerial vehicles capable of self-contained, self-directed flight, and of achieving coordinated behavior in large groups. To that end, the RoboBee is primarily assembled from three main components: Body, Brain, and Colony.
Body development requires constructing robotic insects able to fly on their own with the help of a compact and seamlessly integrated power source; brain development employs “smart” sensors and control electronics that mimic the eyes and antennae of a bee, and can sense and dynamically respond to the environment; the Colony’s focus is about coordinating the behavior of many independent robots so they act as an effective unit.
To construct RoboBees, researchers at the Wyss Institute have come up with many innovative manufacturing methods, so-called Pop-Up microelectromechanical (MEM) technologies that are claimed to have already greatly expanded the boundaries of current robotics design and engineering.
In the very early hours of the morning, in a Harvard robotics laboratory last summer, an insect took flight. Half the size of a paperclip, weighing less than a tenth of a gram, it leapt a few inches, hovered for a moment on fragile, flapping wings, and then sped along a preset route through the air.
Like a proud parent watching a child take its first steps, graduate student Pakpong Chirarattananon immediately captured a video of the fledgling and emailed it to his adviser and colleagues at three a.m.—subject line, “Flight of the RoboBee.”
Inspired by the biology of a fly, with submillimeter-scale anatomy and two wafer-thin wings that flap at 120 times per second, these RoboBees are capable of vertical takeoff, hovering, and steering. The tiny robots flap their wings using piezoelectric actuators—strips of ceramic that expand and contract when an electric field is applied. Thin hinges of plastic embedded within a carbon fiber body frame serve as joints, and a delicately balanced control system commands the rotational motions in the flapping-wing robot, with each wing controlled independently in real-time.
Applications of RoboBees, according to the makers, include distributed environmental monitoring, search-and-rescue operations, and assistance with crop pollination. “I was so excited, I couldn’t sleep,” recalls Chirarattananon, co-lead author of a paper about the robots published recently in “Science.”
The demonstration of the first controlled flight of one of these insect-sized robot is the culmination of more than a decade’s work, led by researchers at the Harvard School of Engineering and Applied Sciences (SEAS) and the Wyss Institute.
“This is what I have been trying to do for literally the last twelve years,” says Robert J. Wood, Charles River Professor of Engineering and Applied Sciences at SEAS, Wyss Core Faculty Member, and principal investigator of the National Science Foundation-supported RoboBee project. “It’s really only because of this lab’s recent breakthroughs in manufacturing, materials, and design that we have even been able to try this. And it just worked, spectacularly well.”
The tiny device is said to not only represent the “absolute cutting edge” of micromanufacturing and control systems, it is an aspiration that has impelled innovation in these fields by dozens of researchers across Harvard for years. “We had to develop solutions from scratch, for everything,” explains Wood. “We would get one component working, but when we moved onto the next, five new problems would arise. It was a moving target.”
Flight muscles, for instance, don’t come prepackaged for robots the size of a fingertip.
“Large robots can run on electromagnetic motors, but at this small scale you have to come up with an alternative, and there wasn’t one,” says Kevin Y. Ma, a graduate student at SEAS.
At tiny scales, small changes in airflow can have an outsized effect on flight dynamics, and the control system has to react that much faster to remain stable.
The robotic insects also take advantage of an innovative manufacturing technique that was developed by Wood’s team in 2011. Sheets of various laser-cut materials are layered and sandwiched together into a thin, flat plate that folds up like a child’s pop-up book into the complete electromechanical structure.
The quick, step-by-step process replaces what used to be a painstaking manual task and permits Wood’s team to use more robust materials in new combinations, while improving the overall precision of each device.
“We can now very rapidly build reliable prototypes, which allows us to be more aggressive in how we test them,” says Ma, adding that the team has gone through twenty prototypes in just the past six months.
The materials, fabrication techniques, and components that emerge along the way might prove to be even more significant. For example, the pop-up manufacturing process could enable a new class of complex medical devices, points out the developers. Harvard’s Office of Technology Development, in collaboration with Harvard SEAS and the Wyss Institute, is already in the process of commercializing some of the underlying technologies.
[Left, autonomous swarms of aerial, small robots could be used to search for and rescue survivors following natural disasters or perform other dangerous tasks. Photo courtesy of Wyss Institute.]
“Harnessing biology to solve real-world problems is what the Wyss Institute is all about,” says Wyss Founding Director Don Ingber. “This work is a beautiful example of how bringing together scientists and engineers from multiple disciplines to carry out research inspired by nature and focused on translation can lead to major technical breakthroughs.”
On a Long Leash
“Now that we’ve got this unique platform, there are dozens of tests that we’re starting to do, including more aggressive control maneuvers and landing,” says Wood.
After that, the next steps will involve integrating the parallel work of many different research teams who are working on the brain, the colony coordination behavior, the power source, and so on, until the robotic insects are fully autonomous and wireless.
The prototypes are still tethered by a very thin power cable because there are no off-the-shelf solutions for energy storage that are small enough to be mounted on the robot’s body. High energy-density fuel cells must be developed before the RoboBees will be able to fly with much independence.
Control, too, is still wired in from a separate computer, though a team led by SEAS faculty Gu-Yeon Wei and David Brooks is working on a computationally efficient brain that can be mounted on the robot’s frame.
“Flies perform some of the most amazing aerobatics in nature using only tiny brains,” notes Sawyer B. Fuller, a postdoctoral researcher on Wood’s team who essentially studies how fruit flies cope with windy days. “Their capabilities exceed what we can do with our robot, so we would like to understand their biology better and apply it to our own work.”
The goal of this first controlled flight represents, for Wood, a validation of the power of his ambitious dreams—set when he was in graduate school. “This project provides a common motivation for scientists and engineers across the university to build smaller batteries, to design more efficient control systems, and to create stronger, more lightweight materials,” says Wood. “You might not expect all of these people to work together: vision experts, biologists, materials scientists, electrical engineers. What do they have in common? Well, they all enjoy solving really hard problems.”
“I want to create something the world has never seen before,” adds Ma. “It’s about the excitement of pushing the limits of what we think we can do, the limits of human ingenuity.”
Harvard roboticists have also demonstrated that their flying microrobots can now perch during flight to save energy—like bats, birds, or butterflies.
“Many applications for small drones require them to stay in the air for extended periods,” said Moritz Graule, a student researcher at the Wyss Institute at the time the study was conducted. “Unfortunately, smaller drones run out of energy quickly. We want to keep them aloft longer without requiring too much additional energy.”
The team found inspiration in nature and simple science.
“A lot of different animals use perching to conserve energy,” said Ma. “But the methods they use to perch, like sticky adhesives or latching with talons, are inappropriate for a paper-clip-size microrobot, as they either require intricate systems with moving parts or high forces for detachment.”
Instead, the team turned to electrostatic adhesion—the same basic science that causes a static-charged sock to cling to a pant leg, or a balloon to stick to a wall.
When you rub a balloon on a wool sweater, the balloon becomes negatively charged. If the charged balloon is brought close to a wall, its negative charge forces some of the wall’s electrons away, leaving the surface positively charged. The attraction between opposite charges then causes the balloon to stick to the wall.
“In the case of the balloon, however, the charges dissipate over time, and the balloon will eventually fall down,” said Graule. “In our system, a small amount of energy is constantly supplied to maintain the attraction.”
The RoboBee has now been upgraded to include an electrode patch and a foam mount that absorbs shock. The new perching components weigh 13.4 mg, bringing the total weight of the robot to about 100 mg—similar to the weight of a real bee. The robot takes off and flies normally. When the electrode patch is supplied with a charge, it can stick to almost any surface, from glass to wood to a leaf. To detach, the power supply is simply switched off.
“One of the biggest advantages of this system is that it doesn’t cause destabilizing forces during disengagement, which is crucial for a robot as small and delicate as ours,” said Graule.
The patch requires about one thousand times less power to perch than it does to hover, dramatically extending the operational life of the robot. Reducing the robot’s power requirements is critical for the researchers, as they work to integrate onboard batteries on untethered RoboBees.
“The use of adhesives that are controllable without complex physical mechanisms, are low power, and can adhere to a large array of surfaces is perfect for robots that are agile yet have limited payload—like the RoboBee,” added Wood. “When making robots the size of insects, simplicity and low power are always key constraints.”
Right now, the RoboBee can only perch under overhangs and on ceilings because the electrostatic patch is attached to the top of the vehicle. Next, the team hopes to change the mechanical design so that the robot can perch on any surface.
“There are more challenges to making a robust, robotic landing system but this experimental result demonstrates a very versatile solution to the problem of keeping flying microrobots operating longer without quickly draining power,” said Ma.
The Wyss Institute emulates Nature’s design principles to engineer new bio-inspired materials and devices with high-impact applications in healthcare, manufacturing, robotics, energy, and sustainable architecture. The Institute works as an alliance among Harvard’s Schools of Medicine, Engineering, and Arts & Sciences, and with other leading clinical and academic institutions in the Boston area.
Pakpong Chirarattananon, Sawyer B. Fuller, Noah Jafferis, Matthew Spenko, and Roy Kornbluh of the Wyss Institute contributed to this article. The research was partly funded by the National Science Foundation and the Wyss Institute.