90 / 92
90
June/July 2016 |
Unmanned Systems Technology
PS
|
The Robotic Hummingbird
G
iven the current requirement
for bird-sized unmanned air
vehicles for surveillance and
similar applications, coupled
with our understanding of
aerodynamics and the latest advancements
in microelectronics and power sources,
designers are now able to miniaturise
flying craft down to a size that is feasible for
flapping wing flight (writes Stewart Mitchell).
David Colman, of the Department
of Aerospace Engineering at Texas
A&M University, has been researching
this area, and he says “Our recent
investigations have proved that biological
flapping wing flight offers superior
manoeuvrability with excellent gust
tolerance and disturbance rejection
capabilities compared with that of
conventional craft.
“Also, flapping wings use several
unsteady aerodynamic phenomena, such
as leading-edge vortices, at low Reynolds
numbers [air boundary layer flow
separation caused by turbulence], that
significantly enhance lift production over
what is seen in steady flow conditions
such as those on conventional aircraft.”
After research into the potential of a
flapping wing micro air vehicle (MAV) in
early 2015, Colman and his colleagues
at the university designed, manufactured
and tested a biologically inspired two-
winged, hover-capable autonomous MAV
which they call the Robotic Hummingbird.
It has a wingspan of 12 in and flaps
at 22 Hz to manoeuvre its 62 g weight.
Wing control is taken care of by a unique
modified five-bar crank-rocker system,
which turns the rotary motion of the
motor into a linear arc (flapping) motion.
The system is similar in principle to a
four-bar crank-rocker linkage but with
an extra shaft that enhances the flapping
amplitude and modulates the right- and
left-wing flapping speed and amplitude
independently. It also means the MAV
can provide more lift than any other
flapping wing aircraft of its size, and has
much more intricate aerial control.
Each wing is made from a lightweight
plastic material, and weighs only 0.85 g.
The wings also have flexible spars that
aid lift by using aeroelasticity, flexing so
as to increase their lift area. A modular
mechanism controls each wing’s flapping
frequency and amplitude independently to
keep it true to its orientation and direction
along a specified course or to hover.
The MAV’s control system incorporates
an autopilot, which auto-stabilises the
craft from almost any orientation using the
response from a series of high feedback-
rate gyros and sensors on board.
“The biggest challenge was to develop
a design with the strength throughout its
components to withstand the large forces
imposed during flapping,” says Colman.
To that end, the main body of the
vehicle, which functions as an anchor
point for all the mechanical subsystems
– including a 29 KV brushless dc motor,
flapping mechanism, actuators and wing
kinematic modulation device – is rapid
prototyped from ABS plastic, giving it a
weight of only 5.3 g. A 2.75 mm diameter
carbon fibre rod protrudes vertically
down from the body to support the base
of the craft on landing.
Results from flight tests on the
Hummingbird in a small enclosure show
that it has better hovering and turning
capabilities than other contemporary
MAVs, which could mean that in the
future we may see MAVs with the same
agility as nature’s own hummingbird.
Now,
here’s a
thing
“
”
The biggest
challenge was
to develop a
design with
the strength to
withstand the
large forces
during flapping