Researchers build flying robotic 'tree helicopter'
A natural samara is positioned next to the
smallest and lightest robotic samara constructed to date. The wing of
the vehicle is similar in size to a natural samara wing. Image credit:
Ulrich, et al.
(PhysOrg.com) -- Many trees disperse their seeds by
releasing "helicopters," those single-winged seeds that are also called
"samaras." As these seeds fall to the ground, their wing causes them to
swirl and spin in a process called autorotation, similar to man-made
helicopters. In a new study, researchers have designed and built a
mechanical samara whose dynamics are very similar to those of nature’s
samaras. After testing the mechanical samara, the researchers then built
a variety of remote-controlled robotic samaras with onboard power
sources.
The researchers, Evan Ulrich, Darryll Pines, and Sean Humbert from
the University of Maryland, have published their study on the robotic
samaras in a recent issue of Bioinspiration & Biomimetics.
The idea for building a flying robotic device based on samaras
originated several years ago, after researchers attempted to scale down
full-size helicopters.
“Full-scale helicopters have a high aerodynamic efficiency,” Ulrich, a PhD candidate, told PhysOrg.com.
“But the aerodynamic efficiency is disproportionate, so a scaled-down
helicopter has stability issues and is unfeasible. Dr. Pines, my
advisor, realized that the simplest system in nature that achieves
vertical flight and can autorotate like a helicopter is the samara,
which is a naturally stable system.”
After further investigating the samara in order to better understand
its flight dynamics, the researchers found that the winged seed is also
one of nature’s most efficient fliers. The samara is a monocopter,
meaning it has a single wing. For this reason, the samara has no
stationary frame of reference, unlike a two-winged helicopter, and
appears to fall in a complex way. However, through free-fall testing,
the researchers could quantitatively measure the samara’s flight
dynamics and use this information to control the samara’s autorotation
and flight path.
After designing and building a mechanical samara, the researchers measured its
flight dynamics in free-fall by dropping it from a height of 12 meters. Then the
scientists used this data to develop three different designs of powered
robotic samaras, ranging in size from 7.5 cm to 0.5 m. In flight tests,
they demonstrated that the carbon fiber-based robotic samaras could be
remotely steered to a desired location by altering the wing pitch, which
changes the radius at which the vehicles turn. The robotic samaras
could also hover, climb, and translate.
The samara-inspired autorotation process has
several advantages compared to other small-scale aircraft that perform
vertical take-off and landing. For instance, the robotic samaras are
extremely damage-tolerant. If they lose power while flying, they can
autorotate down and land without sustaining any damage due to their
flexible structure that deflects upon impact. The robotic samaras are
also passively stable, inexpensive, mechanically simple, and have a high
payload capacity. Flight time is around 30 minutes, but depends on the
battery size.
In the future, Ulrich plans to start a company to license and develop
the technology for commercialization. In addition to developing the
robotic samara into a toy, he said that the device could also have
applications in satellite communications and 3D mapping.
Various designs of robotic samaras. Image credit: Ulrich, et al.
“We
want to take advantage of the autorotation mode since it doesn’t
require power for flight,” he said. “If we can find a vertical column of
air, it can stay aloft indefinitely. One possibility is using it as an
autorotating communications platform to carry small components for
satellites, without the requirement of a huge launch cost.”
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