Fig. D: AC power from tether wires makes a piezo
actuator push and pull the base of a flexible
transmission, flapping wings attached at the top.
half-cycle, making the actuator many times more
efficient. The actuator delivered more than 400
watts per kilogram — about five times the energy of
a real bug’s muscle, and enough to get the project
literally off the ground. Using this technique, Wood
succeeded with a flying robot one year after moving
into his current lab at Harvard.
The way to answer the question of flex, as well as
curvature, proportion, and a dozen other variables,
is simply trial and error. “We’re going to just start
popping wings on and off to correlate design factors
with real lift and drag forces,” he says, proudly showing off a small black velvet stage with an expensive,
high-speed videocamera capable of 10,000 frames
per second. This setup will record highly accurate
positions of the wings as they move in space.
Underneath the platform is a handmade and very
sensitive force sensor to measure the tiny lift and
drag forces from the wings, moment by moment.
The terabytes of data from this equipment will
help Wood construct his next fly, one that will hover
unassisted or use some rudimentary onboard control to maneuver. But right now, with dozens of new
wings to flap on the little black velvet stage, Wood’s
next test subject is getting ready for its close-up.
“The monkey’s off our backs,” he says, describing
the tremendous pressure to show the world that
his bug could fly, and the relief afterward. Now he’s
more clearly. There’s no computer software that can
conduct simulations for this scale. No one has modeled this world adequately, despite the experiments
from biologists in the last decade.
One major unknown is the question of flex. The
large fruit fly model used at Berkeley had stiff wings
because the researchers wanted to limit their variables. But houseflies flap nearly horizontally to gain
lift, flexing a little on the upstroke. (Wood demonstrates with the flat of his hand.) His housefly flexed
its wings during each stroke, using hinge joints in
the wings. Joint stops prevented overtwisting.
Robot fly videos at makezine.com/19/robotflies
Illustrations by Brandon Eum; photograph by J.P. Whitney
Bob Parks ( xbobparksx.com) is a frequent contributor to
MAKE and Wired. He and his son have modeled many flying
machines, but so far nothing smaller than an Estes rocket.
60 Make: Volume 19