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futurity_sci_tech 00817.txt

#ouble-play motion keeps critters stable and agile Animals that push forward and back at the same time aren t wasting effort. They are maximizing both stability and maneuverability simultaneously a new study shows. The finding while it could lead to more agile robots serves primarily to shed light on a question that has baffled biologists: why do animals exert force in ways that don t move them toward their destination? A robot designer would likely avoid the side-to-side sashaying of a running lizard or cockroach movements that seem inefficient. So why do the animals behave this way? A research team led by Johns hopkins university engineers says that the extra exertion isn t necessarily wasteful after all. It allows at least some animals to accomplish a double-play often described as impossible in engineering textbooks. ne of the things they teach you in engineering is that you can't have both stability and maneuverability at the same timesays Noah Cowan the associate professor of mechanical engineering who supervised the research. he Wright Brothers figured this out when they built their early airplanes. They made their planes a little unstable to get the maneuverability they needed. hen an animal or vehicle is stable it resists unwanted changes in direction. On the other hand if it is maneuverable it has the ability to quickly change course when desired. Generally engineers have assumed that a system can rely on one property or the other but not both. Not so. nimals are a lot more clever with their mechanics than we often realizecowan says. y using just a little extra energy to control the opposing forces they create during those small shifts in direction animals seem to increase both stability and maneuverability when they swim run or fly. owan says this discovery reported in the Proceedings of the National Academy of Sciences could help engineers simplify and enhance small robots that fly swim or move on mechanical legs. The scientists used slow-motion video to study the fin movements of the tiny glass knifefish. These shy fish each about 3 inches prefer to hide in tubes and other shelters where they avoid being eaten by predators in their Amazon basin habitat. In a lab the team filmed the fish at 100 frames per second to study how they used their fins to stay in one place in these tubes even when facing a steady flow of water. hat is immediately obvious in the slow-motion videos is that the fish constantly move their fins to produce opposing forces. One region of their fin pushes water forward while the other region pushes the water backwardsays Eric Fortune a professor of biological sciences at the New jersey Institute of technology who was a co-author of the paper. his arrangement is rather counter-intuitive like two propellers fighting against each other. f the fish wants to move forward or backward instead of hovering it can adjust the proportion of fin pushing in either direction. The research team developed a mathematical model that suggested that this odd arrangement enables the animal to improve both stability and maneuverability. The team then tested that model with a robot that mimicked the fish s fin movements. This biomimetic robot was developed in the lab of Malcolm Maciver associate professor of mechanical and biomedical engineering at Northwestern University and a co-author. e are far from duplicating the agility of animals with our most advanced robotsmaciver says. ne exciting implication of this work is that we might be held back in making more agile machines by our assumption that it s wasteful or useless to have forces in directions other than the one we are trying to move in. It turns out to be improved key to agility and stability. he mutually opposing forces that help the knifefish become both stable and maneuverable can also be found in the hovering behavior of hummingbirds and bees says senior author Cowan who directs the Locomotion in Mechanical and Biological Systems Lab at Johns Hopkins Whiting School of engineering. s an engineer I think about animals as incredible living robotssays lead author Shahin Sefati a doctoral student advised by Cowan. t has taken several years of exciting multidisciplinary research during my Phd studies to understand these robots better. he National Science Foundation and Office of Naval Research funded the study d

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