LEO carves out a new type of locomotion somewhere between walking and flying
Researchers at Caltech have built a bipedal robot that
combines walking with flying to create a new type of locomotion, making it
exceptionally nimble and capable of complex movements.
Part walking robot, part flying drone, the newly
developed LEONARDO (short for LEgs ONboARD drOne, or LEO for short) can walk a
slackline, hop, and even ride a skateboard. Developed by a team at Caltech’s Center for Autonomous
Systems and Technologies (CAST), LEO is
the first robot that uses multi-joint legs and propeller-based thrusters to
achieve a fine degree of control over its balance.
A paper about the LEO robot was published online on
October 6 and was featured on the October 2021 cover of Science
Robotics.
“We drew inspiration from nature. Think about the way
birds are able to flap and hop to navigate telephone lines,” says Soon-Jo Chung, corresponding author and Bren Professor of Aerospace and Control and
Dynamical Systems. “A complex yet intriguing behavior happens as birds move
between walking and flying. We wanted to understand and learn from that.”
“There is a similarity between how a human wearing a
jet suit controls their legs and feet when landing or taking off and how LEO
uses synchronized control of distributed propeller-based thrusters and leg
joints,” Chung adds. “We wanted to study the interface of walking and flying
from the dynamics and control standpoint.”
Bipedal robots are able to tackle complex real-world
terrains by using the same sort of movements that humans use, like jumping or
running or even climbing stairs, but they are stymied by rough terrain. Flying
robots easily navigate tough terrain by simply avoiding the ground, but they
face their own set of limitations: high energy consumption during flight and
limited payload capacity. “Robots with a multimodal locomotion ability are able
to move through challenging environments more efficiently than traditional
robots by appropriately switching between their available means of
movement. In particular, LEO aims to bridge the gap between the two
disparate domains of aerial and bipedal locomotion that are not typically
intertwined in existing robotic systems,” says Kyunam Kim, postdoctoral
researcher at Caltech and co-lead author of the Science Robotics paper.
By using a hybrid movement that is somewhere between
walking and flying, the researchers get the best of both worlds in terms of
locomotion. LEO’s lightweight legs take stress off of its thrusters by supporting
the bulk of the weight, but because the thrusters are controlled synchronously
with leg joints, LEO has uncanny balance.
“Based on the types of obstacles it needs to traverse,
LEO can choose to use either walking or flying, or blend the two as needed. In
addition, LEO is capable of performing unusual locomotion maneuvers that even
in humans require a mastery of balance, like walking on a slackline and
skateboarding,” says Patrick Spieler, co-lead author of the Science
Robotics paper and a former member of Chung’s group who is
currently with the Jet Propulsion Laboratory, which is managed by Caltech for
NASA.
LEO stands 2.5 feet tall and is equipped with two legs
that have three actuated joints, along with four propeller thrusters mounted at
an angle at the robot’s shoulders. When a person walks, they adjust the
position and orientation of their legs to cause their center of mass to move
forward while the body’s balance is maintained. LEO walks in this way as well:
the propellers ensure that the robot is upright as it walks, and the leg
actuators change the position of the legs to move the robot’s center of mass
forward through the use of a synchronized walking and flying controller. In
flight, the robot uses its propellers alone and flies like a drone.
“Because of its propellers, you can poke or prod LEO
with a lot of force without actually knocking the robot over,” says
Elena-Sorina Lupu (MS ’21), graduate student at Caltech and co-author of the Science
Robotics paper. The LEO project was started in the summer of
2019 with the authors of the Science Robotics paper and
three Caltech undergraduates who participated in the project through the
Institute’s Summer Undergraduate Research Fellowship (SURF) program.
Next, the team plans to improve the performance of LEO
by creating a more rigid leg design that is capable of supporting more of the
robot’s weight and increasing the thrust force of the propellers. In addition,
they hope to make LEO more autonomous so that the robot can understand how much
of its weight is supported by legs and how much needs to be supported by
propellers when walking on uneven terrain.
The researchers also plan to equip LEO with a newly
developed drone landing control
algorithm that utilizes deep neural networks.
With a better understanding of the environment, LEO could make its own
decisions about the best combination of walking, flying, or hybrid motion that
it should use to move from one place to another based on what is safest and
what uses the least amount of energy.
“Right now, LEO uses propellers to balance during
walking, which means it uses energy fairly inefficiently. We are planning to
improve the leg design to make LEO walk and balance with minimal aid of
propellers,” says Lupu, who will continue working on LEO throughout her PhD
program.
In the real world, the technology designed for LEO
could foster the development of adaptive landing gear systems composed of
controlled leg joints for aerial robots and other types of flying vehicles. The
team envisions that future Mars rotorcraft could be equipped with legged
landing gear so that the body balance of these aerial robots can be maintained
as they land on sloped or uneven terrains, thereby reducing the risk of failure
under challenging landing conditions.
The paper is titled “A bipedal walking
robot that can fly, slackline, and skateboard.” Coauthors also include Alireza Ramezani, former Caltech postdoctoral
scholar and currently an assistant professor at Northeastern
University. This research was supported by the Caltech Gary Clinard
Innovation Fund and Caltech’s Center for Autonomous Systems and Technologies.
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