It may eat flies and stink to high heaven, but if this robot works, it
will be an important step towards making robots fully autonomous.
To survive without human help, a robot needs to be able to generate its
own energy. So Chris Melhuish and his team of robotics experts at the
University of the West of England in Bristol are developing a robot that
catches flies and digests them in a special reactor cell that generates
electricity.
Microbial fuel cells digest flies to generate electricity
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Microbial fuel cells digest flies to generate electricity
So what is the downside? The robot will most likely have to attract the
hapless flies by using a stinking lure concocted from human excrement.
Called EcoBot II, the robot is part of a drive to make "release and
forget" robots that can be sent into dangerous or inhospitable areas to
carry out remote industrial or military monitoring of, say, temperature
or toxic gas concentrations. Sensors on the robot feed a data logger
that periodically radios the results back to a base station.
*Exoskeleton electricity*
The robot's energy source is the sugar in the polysaccharide called
chitin that makes up a fly's exoskeleton. EcoBot II digests the flies in
an array of eight microbial fuel cells (MFCs), which use bacteria from
sewage to break down the sugars, releasing electrons that drive an
electric current (see graphic).
In its present form, EcoBot II still has to be manually fed fistfuls of
dead bluebottles, but the ultimate aim of the UWE robotics team is to
make the droid predatory, using sewage as a bait to catch the flies.
"One of the great things about flies is that you can get them to come to
you," says Melhuish. The team has yet to tackle this, but speculates
that it would involve using a bottleneck-style flytrap with some form of
pump to suck the flies into the digestion chambers.
With a top speed of 10 centimetres per hour, EcoBot II's roving prowess
is still modest to say the least. "Every 12 minutes it gets enough
energy to take a step forwards two centimetres and send a transmission
back," says Melhuish.
But it does not need to catch too many flies to do so, says team member
Ioannis Ieropoulos. In tests, EcoBot II travelled for five days on just
eight fat flies - one in each MFC.
*Donated sewage*
So how do flies get turned into electricity? Each MFC comprises an
anaerobic chamber filled with raw sewage slurry - donated by UWE's local
utility, Wessex Water. The flies become food for the bacteria that
thrive in the slurry.
Enzymes produced by the bacteria break down the chitin to release sugar
molecules. These are then absorbed and metabolised by the bacteria. In
the process, the bacteria release electrons that are harnessed to create
an electric current.
Previous efforts to use carnivorous MFCs to drive a robot included an
abortive UWE effort: the Slugbot. This was designed to hunt slugs on
farms by using imaging systems to spot and grab the pests, and then
deliver them to a digester that produces methane to power a fuel cell.
The electricity generated would have been used to charge the Slugbot
when it arrived at a docking station. But the methane-based system took
too long to produce power, and the team realised that MFCs offered far
more promise.
Elsewhere, researchers in Florida created a train-like robot dubbed Chew
Chew (*New Scientist* print edition, 22 July 2000) that used MFCs to
charge a battery, but the bacteria had to be fed on sugar cubes.
For an autonomous robot to survive in the wild, relying on such refined
foodstuffs is not an option, says Melhuish. EcoBot II, on the other
hand, is the first robot to use unrefined fuel. Just do not stand downwind.