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In the future, it's possible that some unmanned aerial vehicles,
or UAVs, might sport wings that flap like a bird or a butterfly.
The Army Research Lab, or ARL, is testing that concept at the
Spesutie Island Robotics Research Facility on Chesapeake Bay.
John W. Gerdes III, mechanical engineer at the Vehicle
Technology Directorate, has been testing such a UAV, known as Robo-Raven.
He designed the vehicle in collaboration with the University of
Maryland.
During an open house Nov. 3, 2015 Gerdes took Robo-Raven
for three test flights. He held it aloft in his hand, sort of like a
falconer might do. With the other hand, he switched on the
transmitter - the sort found in hobby shops for drones and toy
vehicles.
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John W. Gerdes III, mechanical engineer at the Vehicle Technology Directorate, prepares to fly Robo-Raven at Aberdeen Proving Ground's Spesutie Island Robotics Research Facility on Chesapeake Bay, Md., November 3, 2015. (U.S. Army photo by Todd Lopez)
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The wings started flapping immediately as soon as he
threw it aloft. Up and away it went, flapping around in a
light breeze more like a butterfly than a bird. A gust blew
it backward, but Robo-Raven made course corrections on its
own so that Gerdes continued to maintain nearly full control
of its flight.
After a minute or two, a curious
raptor, possibly a hawk, circled
Robo-Raven from above. At this point, Gerdes decided to land
his mechanical bird. He raised his arm, and Robo-Raven
obediently landed on his outstretched hand.
Raptors,
if given the chance, will destroy Robo-Raven, he said. Once
in the past, he said he flew his bird up to about 300 feet
and a falcon dive bombed it, destroying its gossamer wings.
Once the falcon disappeared, Gerdes launched a second
flight. This time, a flock of seagulls circled it. Gerdes
noted that non-birds of prey will come over to investigate,
but will not attack Robo-Raven - at least not yet.
Unfortunately, Gerdes' landing didn't go as smoothly as the
first and it crashed into the grass nearby. Fortunately, his
half-pound bird sustained no damage. Observers wore hard
hats and goggles, just to be safe.
Had his Robo-Raven
been destroyed in a crash or by a raptor, Gerdes had two
backups, each of which looked similar, but were slightly
different in shape and size for testing.
The third
flight went well and landed back in Gerdes' hand.
WHY DESIGN A FLAPPY BIRD?
"Ultimately, what we're trying to go after is a vehicle
which, at least in part, duplicates some of the great things
animals can do," he said. "The benefit of the flapping air
vehicle is obvious when you look at nature."
Flying creatures are so good at what they
do because of how well in harmony all their subsystems work,
he said. "Everything is perfectly matched to itself so they
are able to perform at the highest possible level, given
their size and weight. We're curious to discover the tricks
they're using."
The challenge is to engineer a
system, which can duplicate that behavior, he added.
Gerdes provided another illustration.
A quad-copter
is great for flying at slow speeds, hovering, maneuvering
and avoiding obstacles, he said. On the other hand, an
airplane is great at flying high, far and fast.
"When
you take either of those platforms out of their intended
mission space they do very poorly," he said. "Animals, on
the other hand, can do all these things quite well." The
reason why is they can reconfigure their wings and orient
themselves to take advantage of the airflow. "All these
different details we're trying to learn about here."
Animals that fly are able to do so because of an enormous
number of muscles and nerves that control their flexible
wing and body, he said. The slightest alteration of a wing
can send a bird soaring hundreds of feet into the air on an
updraft.
"It's extraordinarily difficult to unravel
all of the pieces of that problem," where there are flexible
wings, sensors and controls distributed everywhere, he said.
"It's just too difficult to engineer at this point. But, we
can approach that solution at least."
On the other
hand, Robo-Raven has some advantages over real birds.
For instance, Robo-Raven doesn't need to eat or
reproduce. "Animals make sacrifices that are different that
don't make sense from a robotics standpoint, so it gives me
hope that one day we can do better than an animal," he said.
RAVEN'S DESIGN
Robo-Raven's design is a terrible approach from an
efficiency standpoint, Gerdes said.
For one thing, it
has two motors that independently control each wing. There
are commercial flappy-bird designs that work more
efficiently using just one motor to control both wings. For
example, "you wouldn't drive a car with a different motor on
each wheel. You'd be carrying unnecessary extra weight," he
said.
But from a scientific
standpoint, this approach lets one learn a lot more about
the platform and explore interesting spaces of the design,
which wouldn't be possible with a traditional flapping wing
single-motor design, he said. With a single motor, one can
only speed the wings up and slow them down, which doesn't do
much to inform learning of the system.
So, the goal
is not to build the best flapping wing possible. "It's our
goal to build the most amount of knowledge about
flapping-wing air vehicles as possible."
Robo-Raven's
wings were designed with the help of ARL's 3-D printer.
Gerdes programmed a commercial-off-the-shelf Arduino
micro-controller, which controls the flapping motion.
A hobby shop transmitter and receiver is used to send
and receive commands to Robo-Raven. It can fly for 10 to 15
minutes before the motors overheat.
LOOKING AHEAD
Inside Gerdes' lab is a breadboard with wires connected
to sensors. In about a month, he said he hopes to have a
more robust Robo-Raven that can carry this full suite of
sensors, which will measure altitude, air speed, wing
position, flapping speed, power draw, battery charge,
acceleration, roll and so on.
These sensors will
provide a huge body of data, he said, to begin to get at the
"diabolically hard problem to solve" of flight similar to
birds.
Down the road, he said ARL might come up with
an innovative flexible material that would boost the chance
of bird-like flight. He said the various labs across the
Army collaborate very well on projects like this and others
are aware of what he's doing.
Ultimately in the
future, Gerdes said he wants Soldiers to have a single
platform that's safer, quieter, stealthier, more versatile,
that can do a wide range of missions.
"It's an
exciting project, full of possibilities, but unfortunately
right now, it's not the finished product we're after," he
said. That will be years from now. At that point, the U.S.
Army Aviation and Missile Research, Development and
Engineering Center might work on it.
By U.S. Army David Vergun
Army News Service
Copyright 2015
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