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NewScientist.com



*Self-sustaining killer robot creates a stink*


15:13 09 September 04

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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 
<javascript:displayWindow('/misc/popup_ns.jsp?id=ns99996366F1',271+40,969+40)> 
	
        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.



Duncan Graham-Rowe



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