Hummingbird robots were all the rage a couple of years ago, and now it looks like the little fruit bat will get its turn in the spotlight. This week not one but two research institutions, the Virginia Institute of Technology and Brown University, have announced progress on studies of fruit bat flight patterns that could lead to a new generation of highly maneuverable, energy efficient flying robots.
Just what the world needs, right? If you’re already freaked out about drones and bats, then a drone that looks like a bat will really make your head explode.
What Good Is A Fruit Bat Robot?
Well, you can relax for now. At both institutions, the research is still in its initial stages.
Also consider that the famous “hummingbird robot” introduced by DARPA (the Defense Advanced Research Projects Agency) back in 2011 really does look just like a cute little toy hummingbird, which comes in handy for daytime disguise. Since bats only come out at night, if there are any fruit bat robots lurking around most likely you will not have to look at them, at least not very often.
But seriously, the camouflage factor is a big one when it comes to mobile surveillance robots, and if the Defense Department can’t use them, there are endless possibilities for environmental monitoring and research.
For the record, the fruit bat concept comes under the category of MAVs (micro air vehicles with flapping wings), which are also taking shape in the form of butterfly robots and really-really micro “mosquito” robots.
The Virginia Tech Fruit Bat Robot
The fruit bat is of particular interest in aerial robotics because its flight patterns are unique among flying creatures, as explained by Virginia Tech’s Danesh Tafti:
Bats have different wing shapes and sizes, depending on their evolutionary function. Typically, bats are very agile and can change their flight path very quickly — showing high maneuverability for midflight prey capture, so it’s of interest to know how they do this.
Virginia Tech’s contribution to the field is a study of the physics of fruit bat flight, just published in the journal Physics of Fluids.
The research subject, Cynopterus brachyotis, provided the body model for the straight-line flapping motion that forms the core of the study.
The two-step research involved taking real flight measurements, then running that data through a computer to gauge the relationship between the motion of the wings and the airflow around the wing.
One key finding is that fruit bats have extremely precise control and timing when it comes to adjusting the motion of their wings to maximize the effect of the air flow, changing the shape and size of its wing practically on a flap-by-flap basis.
Time history of coherent vortex formation around the bat wing. Bottom plot shows lift and thrust coefficient variation for a flapping cycle over normalized time.
The Brown University Fruit Bat
The Brown University fruit bat robot is quite a bit more roboty at this point. The research team has engineered an actual robotic bat wing with seven movable joints, which mimics the motion of the Cynopterus brachyotis.
Now might be a good time to point out that this bat falls into the category of short-nosed fruit bats, also known as dog-faced fruit bats, so if you are scared of dogs, bats, and drones, you better start prepping now.
The robotic wing is hooked up to a force transducer in a wind tunnel, which monitors and records the aerodynamic forces that the wing generates.
Those measurements are then stacked up against a record of the power output of the motors controlling the joints in the wings, and the result is an evaluation of the energy required to perform each wing movement.
Do Androids Dream Of Electric Bats?
Philip K. Dick, who famously used global warming as the backdrop for his 1965 novel The Three Stigmata of Palmer Eldritch, also conjured up a world of biomimicry robotic wildlife back in 1968, with Do Androids Dream of Electric Sheep?
We’re still waiting for the answer to that question (not solved in the 1982 movie version, Blade Runner), but in the mean time the Brown team is asking their robot some questions, and getting answers, according to research team leader and graduate student Joseph Bahlman:
We can answer questions like, ‘Does increasing wing beat frequency improve lift and what’s the energetic cost of doing that?’
Preliminary results indicate that the backwards folding motion of the wing on the upstroke helps to save energy, and more detail is expected from forthcoming studies.
The Brown research, btw, is funded by the US Air Force Office of Scientific Research along with the National Science Foundation.
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