WHAT’S THE CHARGE?
Whenever you have something that needs to survive away from the
electrical grid for an extended period of time, batteries are inevitably
the limiting factor, and roboticists from the NIMBUS Lab at the
University of Nebraska-Lincoln have solved the problem with a
quadrotor that can fly around and wirelessly charge up electronics for
you. The type of wireless power that these quadrotors are beaming out
is based on what's called "strongly coupled magnetic resonances."
Basically, you've got two coils of wire: one on the quadrotor, and one on
whatever you want to power or charge (we'll call this the receiver). The
quadrotor drives a current in its coil which generates an oscillating
magnetic field. When the quadrotor gets close enough to the receiver,
the receiver's coil starts to resonate with the magnetic field transmitted
by the quadrotor. That resonance induces a voltage in the coil which the
receiver can use to power its electronics or charge its battery.
Exactly how much power gets from the quadrotor to the receiver
(and how efficient the transmission is) depends largely on how well the
quadrotor can keep close to the optimum transmission distance, which
is about 20 centimeters away from the receiver coil. When everything
works perfectly, the quadrotor can wirelessly transfer about 5. 5 watts of
power with an efficiency of 35 percent — which is easily enough to
power a light. This does, of course, decrease the flight time of the
quadrotor, but the whole point is that it can just fly back to base and
recharge itself. Stationary electronics don't have that option.
As far as applications go, the researchers suggest that this kind of
system would be great for "highway messaging systems, ecological
sensors located in forests, or sensors shallowly embedded underground
or in concrete." UAVs would act as mobile power stations, zipping
around and delivering power to sensors when necessary. Rumor has it
that CyPhy Works (the stealthy startup run by iRobot co-founder Helen
Greiner) is developing UAVs for infrastructure inspection, and it seems like some wireless sensor charging capability would fit
right in with that sort of thing. The researchers are staying busy teaching their quadrotor to autonomously keep a stable hover
at an optimum distance to transfer power to a receiver, which will involve either using something like a camera or feedback
from the power transmission itself. They're also hoping to be able to boost the amount of power the quadrotor can transfer,
and maybe toss in some super capacitors.
Transmitter and receiver coils.
UAV wirelessly transferring power to light a LED.
GETTING INTO THE SWING OF THINGS
One of the ways in which robots are starting to get really useful is
with hauling aerial cargo. Last year, the optionally-manned KMAX made its
first autonomous cargo delivery in Afghanistan, and since it can fly as many
missions as you have fuel to keep it going, it's definitely a safer and more
efficient way to get supplies to troops — especially in dangerous areas.
To move cargo around, helicopters (autonomous or otherwise) often
carry stuff slung beneath them on long ropes. As you can probably imagine,
said cargo often ends up doing all sorts of swinging about, especially if the
helicopter that's carrying it has to maneuver. Researchers from the
University of New Mexico have been developing algorithms that allow
robots to compensate for motion-induced swinging of suspended loads, and are testing them out on real live quadrotors.
Essentially, what the quadrotor is doing here is dynamically adjusting its trajectory to damp out the swinging motion of its
cargo. It's sort of like an upside-down version of pendulum balancing, with maybe a little bit of hinged stick balancing thrown in
for good measure. Next, the researchers plan to see if they can get their algorithms to work on platforms that are less
balanced (and more realistic) which (they say) should be "an important step towards developing the next generation of
autonomous aerial vehicles."
26 SERVO 08.2012