Robotics
| By building a robotic bat wing, Brown researchers have uncovered flight secrets of real bats: the function of ligaments, the elasticity of skin, the structural support of musculature, skeletal flexibility, upstroke, downstroke. These discoveries could impact future designs of small aircraft and other applications. |
The robot, which mimics the wing shape and motion of the lesser dog-faced fruit bat, is designed to flap while attached to a force transducer in a wind tunnel. As the lifelike wing flaps, the force transducer records the aerodynamic forces generated by the moving wing.
By measuring the power output of the three servo motors that control the robot’s seven movable joints, researchers can evaluate the energy required to execute wing movements.
The research showed the robot can match the basic flight parameters of bats, producing enough thrust to overcome drag and enough lift to carry the weight of the animals.
A paper describing the robot and presenting results from preliminary experiments is published in the journal Bioinspiration and Biomimetics. The research was conducted in labs of Brown professors Kenneth Breuer and Sharon Swartz, who are the senior authors on the paper. Breuer, an engineer, and Swartz, a biologist, have studied bat flight and anatomy for years.
The robotic flapper generates data that could never be collected directly from live animals, said Joseph Bahlman, a graduate student at Brown who led the project. Bats can’t fly when connected to instruments that record aerodynamic forces directly, so the researchers had to find another way to capture the animal's flight data.
“We can’t ask a bat to flap at a frequency of eight hertz then raise it to nine hertz so we can see what difference that makes,” Bahlman said. “They don’t really cooperate that way.”
But the model does exactly what the researchers want it to do. They can control each of its movement capabilities — kinematic parameters — individually. That way they can adjust one parameter while keeping the rest constant to isolate the effects.
“We can answer questions like, ‘Does increasing wing beat frequency improve lift and what’s the energetic cost of doing that?’” Bahlman said. “We can directly measure the relationship between these kinematic parameters, aerodynamic forces, and energetics.”
One experiment looked at the aerodynamic effects of wing folding. Bats and some birds fold their wings back during the upstroke. Previous research from Brown had found that folding helped the bats save energy, but how folding affected aerodynamic forces was not clear. Testing with the robot wing shows that folding is all about lift.
In a flapping animal, positive lift is generated by the downstroke, but some of that lift is undone by the subsequent upstroke, which generates negative lift. By running trials with and without wing folding, the robot showed that folding the wing on the upstroke dramatically decreases that negative lift, increasing net lift by 50 percent.
Data like that will not only give new insights into the mechanics of bat flight, it could aid the design of small flapping drone aircraft.
SOURCE Brown University
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