Researchers at Northwestern University have created a robotic fish that can move from swimming forward and backward to swimming vertically almost instantaneously by using a sophisticated, ribbon-like fin. The research team, led by Malcolm MacIver, associate professor of mechanical and biomedical engineering at Northwestern’s McCormick School of Engineering and Applied Science, based their robot on a species of fish called the black ghost knifefish. Planning for the robot, called GhostBot, began when graduate student Oscar Curet observed a knifefish suddenly moving vertically in a tank in MacIver’s lab. “We had only tracked it horizontally before, we wondered how could it be doing this,” said Maclver. Further observations revealed that while the fish only uses one traveling wave along the fin during horizontal motion (forward or backward depending on the direction on the wave), while moving vertically it uses two waves. One of these moves from head to tail, and the other moves tail to head. The two waves collide and stop at the center of the fin. The team then created a computer simulation that showed that when these ‘inward counterpropagating waves’ are generated by the fin, horizontal thrust is canceled and the fluid motion generated by the two waves is funneled into a downward jet from the center of the fin, pushing the body up. The flow structure looks like a mushroom cloud with an inverted jet. The group then hired Kinea Design and worked closely with its co-founder Michael Peshkin to make a forearm-length waterproof robot with 32 motors giving independent control of the 32 artificial fin rays of the lycra-covered artificial fin. (That means the robot has 32 degrees of freedom. In comparison, industrial robot arms typically have less than 10.) Seven months and $200,000 later, the GhostBot came to life. For more information please visit: http://www.northwestern.edu/newscenter/stories/2011/01/robotic-ghost-knifefish.html
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