Engineers create perching bird-like robot

Date:
December 1, 2021
Source:
Stanford University
Summary:
With feet and legs like a peregrine falcon, engineers have created
a robot that can perch and carry objects like a bird.



FULL STORY ==========================================================================
Like snowflakes, no two branches are alike. They can differ in size,
shape and texture; some might be wet or moss-covered or bursting with offshoots. And yet birds can land on just about any of them. This ability
was of great interest to the labs of Stanford University engineers
Mark Cutkosky and David Lentink - - now at University of Groningen in
the Netherlands -- which have both developed technologies inspired by
animal abilities.


========================================================================== "It's not easy to mimic how birds fly and perch," said William Roderick,
PhD '20, who was a graduate student in both labs. "After millions of
years of evolution, they make takeoff and landing look so easy, even
among all of the complexity and variability of the tree branches you
would find in a forest." Years of study on animal-inspired robots in
the Cutkosky Lab and on bird- inspired aerial robots in the Lentink Lab
enabled the researchers to build their own perching robot, detailed
in a paper published Dec. 1 in Science Robotics. When attached to a
quadcopter drone, their "stereotyped nature- inspired aerial grasper,"
or SNAG, forms a robot that can fly around, catch and carry objects and
perch on various surfaces. Showing the potential versatility of this
work, the researchers used it to compare different types of bird toe arrangements and to measure microclimates in a remote Oregon forest.

A bird bot in the forest In the researchers' previous studies of
parrotlets -- the second smallest parrot species -- the diminutive birds
flew back and forth between special perches while being recorded by five high-speed cameras. The perches - - representing a variety of sizes and materials, including wood, foam, sandpaper and Teflon -- also contained
sensors that captured the physical forces associated with the birds'
landings, perching and takeoff.

"What surprised us was that they did the same aerial maneuvers, no matter
what surfaces they were landing on," said Roderick, who is lead author
of the paper.

"They let the feet handle the variability and complexity of the surface
texture itself." This formulaic behavior seen in every bird landing is
why the "S" in SNAG stands for "stereotyped." Just like the parrotlets,
SNAG approaches every landing in the same way. But, in order to account
for the size of the quadcopter, SNAG is based on the legs of a peregrine falcon. In place of bones, it has a 3D-printed structure - - which took
20 iterations to perfect -- and motors and fishing line stand-in for
muscles and tendons.



==========================================================================
Each leg has its own motor for moving back and forth and another to
handle grasping. Inspired by the way tendons route around the ankle in
birds, a similar mechanism in the robot's leg absorbs landing impact
energy and passively converts it into grasping force. The result is
that the robot has an especially strong and high-speed clutch that can
be triggered to close in 20 milliseconds. Once wrapped around a branch,
SNAG's ankles lock and an accelerometer on the right foot reports that
the robot has landed and triggers a balancing algorithm to stabilize it.

During COVID-19, Roderick moved equipment, including a 3D printer, from Lentink's lab at Stanford to rural Oregon where he set up a basement
lab for controlled testing. There, he sent SNAG along a rail system
that launched the robot at different surfaces, at predefined speeds and orientations, to see how it performed in various scenarios. With SNAG
held in place, Roderick also confirmed the robot's ability to catch
objects thrown by hand, including a prey dummy, a corn hole bean bag
and a tennis ball. Lastly, Roderick and SNAG ventured into the nearby
forest for some trial runs in the real world.

Overall, SNAG performed so well that next steps in development would
likely focus on what happens before landing, such as improving the
robot's situational awareness and flight control.

Back to nature There are countless possible applications for this
robot, including search and rescue and wildfire monitoring; it can
also be attached to technologies other than drones. SNAG's proximity to
birds also allows for unique insights into avian biology. For example,
the researchers ran the robot with two different toe arrangements -- anisodactyl, which has three toes in front and one in back, like a
peregrine falcon, and zygodactyl, which has two toes in front and two
in back, like a parrotlet. They found, to their surprise, that there
was very little performance difference between the two.



==========================================================================
For Roderick, whose parents are both biologists, one of the most exciting possible applications for SNAG is in environmental research. To that end,
the researchers also attached a temperature and humidity sensor to the
robot, which Roderick used to record the microclimate in Oregon.

"Part of the underlying motivation of this work was to create tools that
we can use to study the natural world," said Roderick. "If we could
have a robot that could act like a bird, that could unlock completely
new ways of studying the environment." Lentink, who is senior author
of the paper, commended Roderick's persistence in what proved to be a years-long project. "It was really Will talking with several ecologists
at Berkeley six years ago and then writing his NSF Fellowship on
perching aerial robots for environmental monitoring that launched this research," Lentink said. "Will's research has proven to be timely because
there now is a 10 million dollar XPRIZE for this challenge to monitor biodiversity in rainforests." Mark Cutkosky, co-author on this paper,
is the Fletcher Jones Professor in the School of Engineering and a member
of Stanford Bio-X and the Wu Tsai Neurosciences Institute. David Lentink
is co-chair of the Biomimetics group and associate professor of science
and engineering at the University of Groningen in the Netherlands.

This research was funded by the Air Force Office of Scientific Research
and the National Science Foundation.

========================================================================== Story Source: Materials provided by Stanford_University. Original written
by Taylor Kubota.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. W. R. T. Roderick, M. R. Cutkosky, D. Lentink. Bird-inspired dynamic
grasping and perching in arboreal environments. Science Robotics,
2021; 6 (61) DOI: 10.1126/scirobotics.abj7562 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211201145322.htm

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