A small device shaped like Pac-Man can move on the surface of water and around obstacles without a motor. It could lead to the development of small robots for environmental monitoring of lakes and rivers.
at Brown University in Rhode Island and his colleagues built little devices made of plastic and rubber that can be moved in a controllable way by ripples in water.
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The researchers first looked at how five-pointed stars, between 0.6 and 1.1 centimetres in size, move when floating in a tank of water. Ripples produced at the surface by a separate oscillating device caused the stars to simply spin about their centres. But the researchers noticed they could change the direction of this spinning by changing the frequency of the vertical oscillations.
Harris says that this observation made them think that if they changed the objects鈥� shape they could steer them on the rippling surface. They tested this by making a 0.8-centimetre-wide device shaped like Pac-Man, i.e., a disc with a wedge cut-out. Because it had only one opening that the ripples could ricochet within, it moved in arcs instead of spinning.
As the researchers suspected, they could tailor its trajectory by tuning the oscillation frequency. They enabled them to steer the object around posts set up in the tank as a sort of simple obstacle course.
at Columbia University in New York says the approach could be used to make very simple autonomous robots. They could be used to carry sensors or deliver chemicals while taking advantage of naturally occurring ripples on rivers or lakes, he says.
Harris and his colleagues have already tested small 鈥溾�� that include a vibrating part for making ripples by themselves, but they could only move in a straight line. The new Pac-Man shape may be able to change that, he says.
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