Aerial robots have been widely used in remote sensing, search and rescue. However, their inability to land on a branch as easily and steadily as a bird has become a constraint on their further use.
The act of a bird landing on a branch is not simple: each branch is actually different in shape, material, texture, etc. Therefore, landing requires a lot of agility and coordination.
Stanford University engineers Mark Cutkosky and David Lentink have developed a bionic robot based on how birds land: it can perch on complex surfaces and catch irregular objects thrown by humans.
"Airplanes, helicopters, flying cars and aerial robots can only land at special airports and helipads. Birds can land anywhere, and we want to develop a take-off and landing device that can do that." David Lentink told the Paper (www.thepaper.cn).
David Lentink says the robots could be used in the future for fire warning systems, weather pattern monitoring, wildlife behavior research and more. "With the ability to perch in the air, the quadcopter can make longer ecological observations in the forest without running out of battery in flight. This greatly increases the amount of time available for scientific recording."
The study was recently published as a cover paper in Science Robotics, a prestigious academic journal. The title is "Bird-inspired Dynamic grasping and Perching in Arboreal Environments".
For centuries, scientists have studied how birds fly. But only recently have scientists begun to study the mechanisms and behavior of bird habitats.
Previously, researchers studied the flight of parrotlets, small parrots, using five high-speed cameras to record their flight between roosts of a variety of materials. These perches carry sensors that record the mechanical forces associated with landing, perching and taking off.
The study found that birds lift their bodies and stretch their legs before reaching their perch. After making contact with the surface of the perch, the bird controls the strength of its toes to wrap and squeeze the perch and grip on to tiny rough spots on the surface so it doesn't slip. Finally, the birds balance on the perch and adjust their footing as necessary.
"We were surprised that no matter what surface they landed on, they performed the same aerial maneuvers," said Roderick, lead author of the paper. "They handle the variability and complexity of the surface texture with their feet."
In this study, researchers have developed stereotyped nature-inspired Aerial Grasper (SNAG for short) for aerial robots based on the research of bird flight. Similar to birds, SNAG uses stereotyping, passive and active control behaviors to land across a variety of habitats.
SNAG incorporated bird-inspired mechanisms into its two legs to work together and grab a perch when landing. During landing, SNAG balances to stabilize itself and take off safely.
The "bones" of SNAG's "legs" are a 3D-printed structure that has been iterated 20 times, while the "muscles" and "tendons" are motors and fishing lines, respectively. Motors are in each leg to control movement and handle grips. The robot's legs also have a mechanism similar to the tendons near birds' ankles that absorb landing impact energy and passively convert it into grip force.
The robot has a powerful and fast clutch that can trigger a shutdown in 20 milliseconds. Once wrapped around a branch, SNAG's ankle locks, and the accelerometer on its right foot reports it has landed, triggering a balancing algorithm to stabilize it.
During the COVID-19 pandemic, Roderick moved equipment such as 3D printers from Stanford university's Lentink lab to a basement lab in rural Oregon. He fired SNAG robots at specific speeds and directions at different surfaces to test their performance in various scenarios.
The robot can also catch objects thrown by humans, such as models of prey and tennis balls.
Finally, Roderick also ventures into a nearby forest to put SNAG through some real-world testing. Overall, SNAG has done well.
The researchers say one of the most exciting applications of this research is environmental research. Roderick attached a temperature and humidity sensor to the robot to record Oregon's microclimate.
Because the robot can inhabit, it can save energy. Equipped with renewable energy such as solar power, it can perch in a tree to recharge and monitor it for longer periods of time.
The robots could also be used in the future for fire warning systems, weather pattern monitoring, wildlife behavior research and even physical sample collection.
The research could also help with avian biology, such as better understanding of what makes birds so successful.
The researchers designed two robots with different toe arrangements. Anisodactyl has three front toes and one back, like the peregrine falcon, which is the most common foot arrangement; Zygodactyl has two front toes and two back toes, like a parrot. However, they found little difference in performance between the two, suggesting that both arrangements are effective for perching on branches.
As for the next steps, the researchers said they will improve its flight control and situational awareness, as well as its robustness against harsh conditions, such as rain or snow, to enable the robot to perform better in natural environments.
Lentink said it will develop a version of the robot that can participate in the XPRIZE Rainforest challenge, which monitors biodiversity and climate change.
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