Source: Wyss Institute

By Leah Burrows, SEAS Communications

In a recent article in Science, Harvard roboticists demonstrate that their flying microrobots, nicknamed the RoboBees, 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, first author of the paper, who was a student researcher at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering at Harvard University 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 co-author Kevin Ma, Ph.D., a Postdoctoral Researcher at SEAS and the Wyss Institute. “But the methods they use to perch, like sticky adhesives or latching with talons, are inappropriate for a paperclip-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, initially pioneered at the Harvard Microrobotics Lab, has now been updated 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 100mg — 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 1000 times less power to perch than it does to hover, offering to dramatically extend 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 Robert Wood, Ph.D., Charles River Professor of Engineering and Applied Sciences at SEAS and a Core Faculty member at the Wyss Institute, and senior author of the study. “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, as 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.

References:

The paper was coauthored by Pakpong Chirarattananon, Sawyer B. Fuller, Noah Jafferis, Matthew Spenko and Roy Kornbluh. The research was funded by the National Science Foundation, the Wyss Institute for Biologically Inspired Engineering, and the Swiss Study Foundation.

Source: Wyss Institute at Harvard University

In the Disruptive Podcast series, Terrence McNally speaks directly with Wyss Institute researchers, exploring what motivates them and how they envision our future as might be impacted by their disruptive technologies. In part 2 of the Disruptive: Bioinspired Robotics episode, Wyss Founding Core Faculty Member Robert Wood discusses new manufacturing techniques that are enabling popup and soft robots.

Wood is developing biologically inspired aerial and terrestrial microrobots, soft-bodied robots, and “printable” robots. His current research interests include new micro- and meso-scale manufacturing techniques, fluid mechanics of low Reynolds number flapping wings, control of sensor-limited and computation-limited systems, active soft materials, and morphable soft-bodied robots. He leads a team of over 40 researchers on the National Science Foundation (NSF) “RoboBees” project to develop coordinated colonies of autonomous robotic bees.

His group is also building agile ambulatory robots that are inspired by insects and centipedes. The long-term goal is to create a swarm of robotic insects capable of performing important tasks, such as search and rescue, hazardous environmental explorations, and pollination. Wood is collaborating with a diverse set of researchers at the Wyss who are exploring soft-bodied autonomous robots and soft devices for human-robot interaction and rehabilitation. One of these projects, called “Second Skin,” is a system in which sensing, actuation, and control mechanisms are embedded in soft devices that can be worn by patients with neuromuscular disorders to help them regain function. Wood is also working on novel manufacturing processes for “printable robots” with the goal of automating robot development and creating new methods for rapid prototyping complex electromechanical devices.

By Leah Burrows | SEAS Communications

Engineers have been trying to design functional aerial-aquatic vehicles for decades with little success. The biggest challenge is conflicting design requirements: aerial vehicles require large airfoils like wings or sails to generate lift while underwater vehicles need to minimize surface area to reduce drag.

To solve this, engineers at the Harvard John A. Paulson School of Engineering and Applied Science (SEAS) and the Wyss Institute for Biologically Inspired Engineering at Harvard University took a clue from puffins. The birds with flamboyant-colored beaks are one of nature’s most adept hybrid locomotors, employing similar flapping motions to propel themselves through air as well as through water to dive for fish.

“Through various theoretical, computational and experimental studies, we found that the mechanics of flapping propulsion are actually very similar in air and in water,” said Kevin Chen, a graduate student in the Harvard Microrobotics Lab at SEAS. “In both cases, the wing is moving back and forth. The only difference is the speed at which the wing flaps.”

RoboBee: From Aerial to Aquatic from Wyss Institute on Vimeo.

Applying this in the lab, the team of researchers at SEAS and Wyss have demonstrated the first flying, swimming, insect-like robot — paving the way for future duel aerial aquatic robotic vehicles. The aerial-aquatic robot is an adaptation of the previously developed “RoboBee”, a microrobot smaller than a paperclip that flies and hovers like an insect, flapping its tiny, nearly invisible wings 120 times per second.

The new research was presented recently in a paper at the International Conference on Intelligent Robots and Systems in Germany, where first author Chen accepted the award for best student paper. The paper was co-authored by SEAS/Wyss graduate student Farrell Helbling, SEAS/Wyss postdoctoral fellows Nick Gravish and Kevin Ma, and Robert J. Wood, who is the founder of the Harvard Microrobotics Lab, the Charles River Professor of Engineering and Applied Sciences at SEAS, and a Core Faculty Member at the Wyss Institute.

In order to make the transition from air to water, the team first had to solve the problem of surface tension. The RoboBee, designed in Wood’s lab, is so small and lightweight that it cannot break the surface tension of the water. To overcome this hurdle, the RoboBee hovers over the water at an angle, momentarily switches off its wings, and crashes unceremoniously into the water in order to sink.

Next, the team had to account for water’s increased density. “Water is almost 1,000 times denser than air and would snap the wing off the RoboBee if we didn’t adjust its flapping speed,” said Helbling, the paper’s second author.

The team lowered the wing speed from 120 flaps per second to nine but kept the flapping mechanisms and hinge design the same. A swimming RoboBee changes its direction by adjusting the stroke angle of the wings, the same way it does in air. Like a flying version, it is still tethered to a power source. The team prevented the RoboBee from shorting by using deionized water and coating the electrical connections with glue.

While this RoboBee can move seamlessly from air to water, it cannot yet transition from water to air. Solving that design challenge is the next phase of the research, according to Chen.

“What is really exciting about this research is that our analysis of flapping-wing locomotion is not limited to insect-scaled vehicles,” said Chen. “From millimeter-scaled insects to meter-scaled fishes and birds, flapping locomotion spans a range of sizes. This strategy has the potential to be adapted to larger aerial-aquatic robotic designs.”

“Bioinspired robots, such as the RoboBee, are invaluable tools for a host of interesting experiments — in this case on the fluid mechanics of flapping foils in different fluids,” said Wood. “This is all enabled by the ability to construct complex devices that faithfully recreate some of the features of organisms of interest.”

This research was funded by the National Science Foundation and the Wyss Institute for Biologically Inspired Engineering.