Tech Briefs Magazine - August 2023 - 27

Training a Quadrotor Drone to Cope with Collisions
Such drones could be used not only for search and rescue but also monitoring forest fires,
aiding military reconnaissance, and even exploring the surface of other planets.
Arizona State University, Tempe, AZ
A
dvanced technology plays a vital role in search and rescue
operations after natural disasters such as earthquakes. Thermal
imaging equipment and sensitive listening devices are deployed
to seek out signs of life. Small aerial drones could also
survey otherwise inaccessible spaces, but the inherent fragility of
current designs have limited their use.
" We see drones used to assess damage from high in the sky,
but they can't really navigate through collapsed buildings, " said
Wenlong Zhang, an Associate Professor in the Ira A. Fulton
Schools of Engineering at Arizona State University. " Their rigid
frames compromise resilience to collision, so bumping into
posts, beams, pipes, or cables in a wrecked structure is often
catastrophic. They don't recover; they crash. "
Zhang said aerial drones need to endure knocks and jolts to
achieve their potential for search and rescue operations. Toward
that end, he and his lab team have designed and tested a first-ofits-kind
quadrotor drone with an inflatable frame. Uniquely, it's
stiffness is tunable or adjustable to absorb and recover from unexpected
taps and thumps.
" We need to change our focus on avoiding environmental
contact. Drones need to physically interact with their surroundings
to accomplish a range of tasks, " Zhang said. " A soft body
not only absorbs impact forces to provide collision resilience; it
also offers the material compliance necessary for dynamic maneuvers
such as perching. "
Perching is an example of controlled collision. Birds technically
collide with tree branches or other structures as they land
and perch. Their compliant joints and soft tissues absorb the impact
force, and a passive locking mechanism in their feet enables
them to grasp onto irregular surfaces without using muscular
energy to hold them in place.
Zhang and his team drew inspiration from this avian model
to design a hybrid fabric-based bistable grasper for their new
aerial drone. Bistable means it has two unpowered resting
states: open and closed. It simply reacts to the impact of landing
by snapping closed and securely gripping onto objects of
various shapes and sizes.
" It can perch on pretty much anything. Also, the bistable material
means it doesn't need an actuator to provide power to hold its
perch. It just closes and stays like that without consuming any energy, "
Zhang said. " Then when needed, the gripper can be pneumatically
retracted and the drone can just take off. "
This kind of contact-reactive, unpowered perching is important
for sustained operations in the field. Drones can position themselves
wherever required, and then turn off their rotors to conserve
battery power.
According to Zhang, such dynamic environmental interaction
can enhance the use of drones in search and rescue operations,
but also for other purposes such as monitoring forest
fires, aiding military reconnaissance and even exploring the
surface of other planets.
" There are so many functionalities possible with conformable,
reconfigurable soft aerial robots, so we hope our work here leads
to even more novel, bio-inspired designs, " Zhang said.
For more information, contact Gary Werner at gary.werner@
asu.edu; 480-727-5622.
Arizona State University Associate Professor Wenlong Zhang and his team
have developed a first-of-its kind quadrotor drone with both an inflatable
frame to enable resilience to collisions and an innovative gripper than
enables the device to securely perch on almost any surface. (Image: Arizona
State University)
Tech Briefs, August 2023
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