bots IN BRIEF
SERVO 11.2015 17
HARVARD ROBOBEE ALL THE BUZZ
For the last several years, Harvard has been developing a robot bee and they’ve done some impressive work. Their
sub-paper-clip-sized 100 milligram flapping wing micro aerial
vehicle is fully controllable down to a stable autonomous
hover. It’s still tethered for power and there’s no onboard
autonomous control, but the robot flaps its wings and flies
like an insect which is pretty darn cool.
Tiny robotic bugs have lots of potential for search and
rescue, surveillance, and exploration, but what’s been all the
rage recently is adaptive multi-modal robotics: Robots that
can creatively handle a combination of terrains, making them
much more versatile. With some exceptions, robots are
usually pretty bad at this, and with some exceptions, humans
and animals are too. There are ground robots that can handle
water and a few flying robots that aren’t totally helpless on
the ground, but so far, we haven’t seen much in the way of
flying robots that are good swimmers.
At the recent IROS (Intelligent Robots and Systems)
conference, Harvard researchers presented a paper describing
how they managed to get their robotic bee to swim, which is
not really a thing that even real bees are known for doing.
With no hardware modifications at all, Harvard’s RoboBee
can fly through the air, crash land in the water, and turn into a
little submarine.
RoboBee is small enough to sit on the tip of your finger,
and light enough that you’d barely feel it if it was. When it flies
(or swims), it’s doing so under full control. A motion capture
system tracks its position and sends trajectory commands to
the robot. This works in both air and water, and RoboBee’s
method of entry (a pitch-over, dive, crash, and sink) is
deliberate.
The key realization here is that swimming is actually a lot
like flying. In both cases, you’re trying to propel yourself
through a fluid by moving a wing (or fin) back and forth. To fly
(and particularly to hover), you need to do this very quickly,
but to swim it’s a much more relaxed motion. Fundamentally,
it’s the same motion, though, and you can achieve it with the
same basic hardware. In the case of RoboBee, to fly in air, it
flaps its wings at 120 Hz, while to swim in water, it flaps its
wings at just 9 Hz. Otherwise, the three-axis torque control is
very similar, meaning that the robot can be steered around in
the water, too.
One unique problem that RoboBee has with the water
entry is that it’s so small, the surface tension of the water is
enough to keep it from submerging. This is part of the reason
that it has to crash land in water (it also needs to have its
wings treated with a surfactant to help it sink).
A fully loaded RoboBee (with a battery on board) might
be heavy enough to avoid this problem, but at this point it’s
still an issue. Also still an issue is the whole water-air
transition, which seems like it’s significantly more difficult than
going from air to water, but we’ve been assured that the
researchers will be tackling this in future work.
Images courtesy of
Wyss Institute/
Harvard University.
