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Could the future of robotics be a toy train with a taste for flesh?

BEWARE: a hungry, flesh-eating robot called Chew Chew could have designs on you. Not that you won't hear the beast coming: Chew Chew is a 12-wheeled monster that looks more like a train. But he's also the first robot to be completely powered by food. He's called a gastrobot--and he is set to make his public debut in August, at a robotics conference in Hawaii.

Chew Chew's "stomach" is a microbial fuel cell (MFC), a device that enslaves a population of bacteria, in this case E. coli, to break down food and convert chemical energy into electricity. The ideal fuel, in terms of energy gain, is meat, says inventor Stuart Wilkinson of the University of South Florida in Tampa. "Vegetation is not nearly as nutritious," he explains. But eating meat requires you to catch it first and that, in turn, requires a lot of extra energy and complex behaviours, he says.

Early applications for gastrobots are likely to include mowing lawns--and grazing on grass clippings for fuel. The long-term idea is to develop autonomous robots that can feed themselves, says Wilkinson.

The robot consists of three wheeled wagons, each about a metre long. For convenience, says Wilkinson, Chew Chew only eats sugar cubes at the moment because these are almost entirely broken down by the microbes, producing virtually no waste.

The microbes produce enzymes that break down carbohydrates. "Every time you break a large molecule like glucose into smaller molecules you release electrons," he says. These electrons are harnessed to charge a battery by a reduction and oxidation (redox) reaction. Wilkinson says this is analogous to blood supply and respiration in a mammal--but delivering electrons instead of oxygen.

Although Chew Chew doesn't produce much in the way of waste--just carbon dioxide and water--it would produce more if it ate vegetation or meat, says Wilkinson.

"At the moment," says Wilkinson, "we have to feed it like a baby because it doesn't have any arms or legs." In fact, as robots go, Chew Chew is a bit of an underachiever. The MFC does not produce enough power to move it, so instead the electricity is used to charge its batteries. Only when the batteries are fully charged does the robot have enough power to move forward. When the batteries are drained, the cycle repeats itself.

"Turning food into electricity isn't unique," he says. "What I've done is make it small enough to fit into a robot."

Wilkinson says the gastrobot also differs from other projects, such as the slug-eating robot being developed at the University of the West of England in Bristol, because it does its digestion on-board. This makes a lot more sense in terms of energy efficiency than shuttling back and forth between your quarry and the MFC.

Chris Melhuish of the slugbot team says that the potential is there to use this sort of technology for vehicles, but it's a long way off. "The energy demands would be huge to run a train or even a small car," he says. Perhaps it would be more practical to build an underwater robot. "If a robot fish could be built then it would make more sense to build a robot which ate fish and monitored beaches for sharks." But Wilkinson doesn't think it's good to give gastrobots a taste for meat. "Otherwise they'll notice there's an awful lot of humans running around and try to eat them," he warns.

Duncan Graham-Rowe

From New Scientist magazine, 22 July 2000.

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