Robotic fish can be a valuable tool in the fight against one of the world’s most problematic invasive species, the mosquitofish, researchers report.
Invasive species control is notoriously challenging, especially in lakes and rivers where native fish and other wildlife have limited options for escape.
Soaring mosquitofish populations in freshwater lakes and rivers worldwide have decimated native fish and amphibian populations, and attempts to control the species through toxicants or trapping often fail or cause harm to local wildlife.
A robot fish that mimics a predator largemouth bass may be a valuable tool in the fight against one of the world’s most problematic invasive species, the mosquitofish. (Credit: NYU)
Stress as a weapon against invasive species
Researchers have published the first experiments to gauge the ability of a biologically inspired robotic fish to induce fear-related changes in mosquitofish. Their findings indicate that even brief exposure to a robotic replica of the mosquitofish’s primary predator—the largemouth bass—can provoke meaningful stress responses in mosquitofish, triggering avoidance behaviors and physiological changes associated with the loss of energy reserves, potentially translating into lower rates of reproduction.
“To the best of our knowledge, this is the first study using robots to evoke fear responses in this invasive species,” says Maurizio Porfiri, professor at the Tandon School of Engineering at New York University. “The results show that a robotic fish that closely replicates the swimming patterns and visual appearance of the largemouth bass has a powerful, lasting impact on mosquitofish in the lab setting.”
The team exposed groups of mosquitofish to a robotic largemouth bass for one 15-minute session per week for six consecutive weeks. The robot’s behavior varied between trials, spanning several degrees of biomimicry. Notably, in some trials, the researchers programmed the robot to incorporate real-time feedback based on interactions with live mosquitofish and to exhibit “attacks” typical of predatory behavior—a rapid increase in swimming speed.
Researchers tracked interactions between the live fish and the replica in real time and analyzed them to reveal correlations between the degree of biomimicry in the robot and the level of stress response the live fish exhibited. Fear-related behaviors in mosquitofish include freezing (not swimming), hesitancy in exploring open spaces that are unfamiliar, and potentially dangerous, and erratic swimming patterns.
Freaked out fish
The researchers also measured physiologic parameters of stress response, anesthetizing the fish weekly to measure their weight and length. Decreases in weight indicate a stronger anti-predator response and result in lower energy reserves. Fish with lower reserves are less likely to survive long and devote energy toward future reproduction—factors with strong implications for population management in the wild.
Fish exposed to robotic predators that most closely mimicked the aggressive, attack-oriented swimming patterns of real-life predators displayed the highest levels of behavioral and physiological stress responses.
“Further studies are needed to determine if these effects translate to wild populations, but this is a concrete demonstration of the potential of robotics to solve the mosquitofish problem,” says lead author Giovanni Polverino, a fellow in the biological sciences department at the University of Western Australia. “We have a lot more work going on between our schools to establish new, effective tools to combat the spread of invasive species.”
Porfiri’s Dynamical Systems Laboratory is known for previous work using biomimetic robots alongside live fish to tease out the mechanisms of many collective animal behaviors, including leadership, mating preferences, and even the impact of alcohol on social behaviors. In addition to developing robots that offer fully controllable stimuli for studying animal behavior, the biomimetic robots minimize use of experimental animals.
Additional researchers came from NYU and the University of Western Australia. The National Science Foundation and the Forrest Research Foundation supported the research.
The way birds can successfully perch on the Teflon and other materials is teaching researchers how they might create flying robots that land like a bird.
Under the watchful eyes of five high-speed cameras, a small, pale-blue bird named Gary waits for the signal to fly. Diana Chin, a graduate student at Stanford University and Gary’s trainer, points her finger to a perch about 20 inches away. The catch here is that the perch is covered in Teflon, making it seemingly impossible to stably grasp.
Gary’s successful touchdown could help researcher build better flying robots.
“Modern aerial robots usually need either a runway or a flat surface for easy takeoff and landing. For a bird, almost everywhere is a potential landing spot, even in cities,” says Chin, part of the lab of David Lentink, assistant professor of mechanical engineering. “We really wanted to understand how they accomplish that and the dynamics and forces that are involved.”
Stick the landing
Even the most advanced robots come nowhere near the grasping ability of animals when dealing with objects of varying shapes, sizes, and textures. So, the researchers gathered data about how Gary and two other birds land on different kinds of surfaces, including a variety of natural perches and artificial perches covered in foam, sandpaper, and Teflon.
“This is not unlike asking an Olympic gymnast to land on Teflon-covered high bars without chalking their hands,” says Lentink, senior author of the paper in eLife. Yet, the parrotlets made what seems almost impossible for a human look effortless.
The findings also include detailed studies of how the birds’ claws and feet produce friction. From this work, the researchers found that the secret to the parrotlet’s perching versatility is in the grip.
“When we look at a person running, a squirrel jumping, or a bird flying, it is clear that we have a long way to go before our technology can reach the complex potential of these animals, both in terms of efficiency and controlled athleticism,” says William Roderick, a graduate student in mechanical engineering in the Lentink lab and in the lab of Mark Cutkosky, chair in the School of Engineering.
“Through studying natural systems that have evolved over millions of years, we can make tremendous strides toward constructing systems with unprecedented capabilities.”
It’s all in the grip
The perches researchers used in the study aren’t your average pet store stock. The researchers split them in two, lengthwise, at the point that approximately aligned with the center of a parrotlet’s foot. As far as the bird was concerned, the perches felt like a single branch but each half sat atop its own 6-axis force/torque sensor.
This meant the researchers could capture the total forces the bird put on the perch in many directions and how those forces differed between the halves—which indicated how hard the birds were squeezing.
After the birds flapped to all nine force-sensing perches of assorted size, softness, and slipperiness, the group began analyzing the first stages of landing. Comparing different perch surfaces, they expected to see differences in how the birds approached the perch and the force with which they landed, but that’s not what they found.
“When we first processed all of our data on approach speed and the forces when the bird was landing, we didn’t see any obvious differences,” Chin says. “But then we started to look into kinematics of the feet and claws—the details of how they moved those—and discovered they adapt them to stick the landing.”
The extent to which the birds wrapped their toes and curled their claws varied depending on what they encountered upon landing. On rough or squishy surfaces—such as the medium-size foam, sandpaper, and rough wood perches—their feet could generate high squeeze forces with little help from their claws.
On perches that were hardest to grasp—the floss-silk wood, Teflon, and large birch—the birds curled their claws more, dragging them along the perch surface until they had secure footing.
This variable grip suggests that, when building robots to land on a variety of surfaces, researchers could separate the control of approaching landing from the actions required for a successful touchdown.
Their measurements also showed that the birds can reposition their claws from one graspable bump or pit to another in a mere 1 to 2 milliseconds. (For comparison, it takes a human about 100 to 400 milliseconds to blink.)
Flying robots taking off
The researchers have already begun characterizing how parrotlets take off from the different surfaces. Combined with their previous work exploring how parrotlets navigate their environment, the group hopes the findings can lead to more nimble flying robots.
“If we can apply all that we learn, we can develop bimodal robots that can transition to and from the air in a wide range of different environments and increase the versatility of aerial robots that we have today,” Chin says.
Toward that end, Roderick is working on designing the mechanisms that would mimic the birds’ gripping form and physics.
“One application of this work that I’m interested in is having perching robots that can act as a team of tiny little scientists that make recordings, autonomously, for field research in forests or jungles,” he says.
“I really enjoy drawing from the fundamentals of engineering and applying them to new fields to push the limits of what has been previously achieved and what is known.”
The National Science Foundation, the Air Force Office of Scientific Research, the Department of Mechanical Engineering at Stanford, and the Department of Defense funded the work.
Researchers are working to make sure a seeing, hearing, door-opening robot called “ANYmal” can also function in extreme conditions—a mission that takes them to the labyrinth of drains and tunnels below Zurich.
Their aim is to determine whether ANYmal—a robot that ANYbotics, an ETH Zurich spin-off company, jointly developed with Robotic Systems Lab—could one day be useful in sewer systems. It might, for instance, help city of Zurich employees who regularly have to walk or crawl through the some 62 miles of accessible shafts and drains underneath the city and whose job it is to check the walls and floors for damage.
ANYmal on its first tour of inspection in Zurich’s sewer system (Credit: Daniel Winkler/ETH Zurich)
This work not only poses a health risk, but is also potentially lethal, given that the drains can fill up with water very quickly without warning. Another advantage of robots in such an environment is that they could operate in narrow sewers that are not accessible with current technology.
Going down
The researchers place the robot upright at the bottom of the shaft. It is about 19.5 inches tall and has four articulated legs as well as something resembling a head that consists of a camera and various sensors.
Peter Fankhauser, cofounder of ANYbotics, radios his colleagues on the surface, who are responsible for coordinating the test and sending commands to the robot. Fankhauser then twiddles with a joystick and the robot plods forward. As this is the first test in unknown terrain, he takes partial control of the robot even though it is capable of moving autonomously.
“It’s a precautionary measure,” says Fankhauser, “Just because something works in the lab doesn’t always mean it will in the real world.”
(Credit: Daniel Winkler/ETH Zurich)
After all, the conditions underground are not what the robot is used to: the chamber is wet and slippery, with lower temperatures and higher humidity than in the lab. What’s more, it’s very, very dark.
“It’s hard to distinguish much down here,” says Fankhauser, almost with a hint of resignation in his voice, as the robot moves at a slow pace through the roughly 10-foot by 16-foot tunnel.
The robot emits a uniform electromechanical sound—a kind of rhythmic whirring—that blends with the sound of rushing water emanating from the main sewer nearby. Given that the robot is on its maiden test run 13 feet below ground level, the researchers have taken the precaution of avoiding large volumes of water.
In the dark
The goal of the three-year research project, called THING (sub-Terranean Haptic InvestiGator), is to design robots that can move about on their own and are better able to identify their surroundings.
Robots generally use 3D cameras and laser sensors for orientation. But such devices can malfunction in adverse conditions—such as when the ground surface is wet or the air full of dust. That’s why the researchers consider enhanced haptic perception—orientation by touch—to be a possible solution.
Researchers at other institutions are also working with and testing ANYmal. In addition to the tests in the sewerage system, next year researchers will deploy the robot in a Polish copper mine. That will determine whether it can function in an entirely different microclimate, one characterized by hot, dusty air and gravel surfaces.
(Credit: Daniel Winkler/ETH Zurich)
One of the key questions on this first day of testing is whether the robot can find its way around at all in the darkness of the sewerage system. Initially, two helpers with big LED lamps illuminate the surroundings so that the researchers can clearly see what’s going on.
Then, Fankhauser asks the helpers to turn off the lamps and radios his colleagues on the surface to tell the robot to use its own lights. The robot’s sense of touch isn’t the only thing that helps it find its way in the dark, as Marco Hutter, who has been conducting research into legged robots for many years at ETH Zurich, explains: “The robot uses laser sensors and cameras to scan its surroundings. By identifying irregularities in the surface of the concrete, it can determine where it is at any given moment.”
All that the researchers can see in the darkness now are the small round LEDs in the robot’s “head.” The atmosphere is other-worldly: the darkness, the sound of rushing water, the electromechanical whirring, the robot’s LED eyes. Then someone breaks the eerie silence with a droll comment: “Its eyes are a bit like a Rottweiler.”
ANYmal’s future missions
Researchers completed the first ANYmal prototype was completed in 2015. They carry out on-site tests two or three times a month. For instance, Fankhauser and some members of his team recently headed to an offshore platform in the middle of the North Sea. The hope is that robots could one day perform inspections on such platforms. On its pilot run at least, ANYmal autonomously completed several inspection routes with flying colors.
After almost ten years of research, there’s a lot ANYmal can do. It can not only walk autonomously, but also boasts the sensory capabilities of sight, hearing, and touch. These enable it, for instance, to read the air pressure display on a machine, identify sounds, and recognize objects—for example to determine whether or not a fire extinguisher is in the right place. The robot can even perform certain manual tasks on its own.
Equipped with an additional gripping arm, it can open doors, dispose of refuse, or press a lift button. It also delivers data that is more precise than our own eyes, ears, and noses can perceive. It can identify the ambient temperature and detect the presence of gases in the air. Its latest trick is recognizing the composition of the ground beneath it. “Some of its powers are superhuman,” says Fankhauser.
Despite the lack of light in the sewer, the robot seems to be finding its way quite well, plodding through the shallow channel at a leisurely pace. When the high-tech machine reaches a 20-centimeter-high ledge (just under 8 inches) in a dry side arm of the sewer, Fankhauser brings it to a halt with a flick of the joystick. Initially, he is reluctant to give the robot the command to climb over the ledge. Although it has easily mastered this maneuver in laboratory conditions, down here it is a risky undertaking.
“It’s an expensive machine,” says Fankhauser. But he gives it a try anyway. ANYmal doesn’t manage it at its first attempt. It stops at the ledge like a horse balking at a jump. “Default, start again,” radios Fankhauser. Now the robot elegantly places one leg after another over the ledge.
Watching from the surface
Sitting on a bench under a white canopy on the surface, two assistants have their eyes firmly fixed on a laptop. A generator is buzzing and a router is blinking—and many a cyclist passes by along the main road looking on in bemusement at the hubbub around the open manhole at the side of the road.
Looking over the researchers’ shoulders, you can see an almost constant stream of data flickering across the screen. And thanks to state-of-the-art 3D and laser technologies, live images the robot constantly transmits from underground are visible on a separate monitor.
When Fankhauser radios from below that he wants the robot to touch the wall of the sewer with one of its legs, the two assistants have their work cut out for them. The researchers haven’t programmed software they are using hasn’t been programmed for this. They respond quickly, however, taking an algorithm originally programmed to teach ANYmal to shake hands. But to make sure the robot doesn’t hit the wall with force, the researchers have to adapt the parameters.
In this case, the problem is the angle at which the robot is to raise its leg. One of the assistants types in 100 and then gradually ratchets up the number. At 180 the perfect level is reached and the robot’s maneuver is successful.
“The robot was in nonstop operation and collected a lot of data,” says Fankhauser as he undoes his high rubber boots and removes his protective clothing.
Hutter is satisfied, too: “All the teams will be taking home a huge volume of data to incorporate in their research.”
They are now one step closer to their goal of delivering a robot that can function properly in challenging conditions underground. But their work is far from finished. The robot recorded 500,000 measurements per second over the course of the day. “That’s enough data to keep us busy for six months,” says Fankhauser with a laugh.
Hutter received support from ETH soon after embarking on this research in the form of an ESOP scholarship and a Pioneer fellowship.
