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Robotic Bat Wing Developed to Simulate Flight Dynamics

Flying bat and robotic wing (Brown University)

Flying bat and robotic wing (Brown University)

Biologists and engineers at Brown University in Providence created a robotic bat wing that simulates the aerodynamics of bats, but can also be applied to the design of small pilotless aircraft. The team from the labs of Brown engineer Kenneth Breuer and biologist Sharon Swartz published results from early experiments with the device in the journal Bioinspiration and Biomimetics (free registration for 30 day access required).

Biology graduate student and first author Joseph Bahlman modeled the robotic wing on the lesser dog-faced fruit bat, a species most commonly found in Asia. A bat’s wing spans almost the entire length of the animal, and are supported by two arm bones and five digits somewhat resembling fingers. Over this frame is an elastic skin that can stretch 400 percent without tearing.

The Brown robotic wing mimics the skeleton of a bat’s wing, fabricated on a three-dimensional printer to match the proportions of a real bat, and covered with an elastic polymer skin. The robotic wing has three servo motors that control the motion and position of the device’s seven movable joints (a real bat’s wing has 25 joints). Bahlman’s device operates in a wind tunnel, where instruments measure the aerodynamic forces generated by the moving wing, particularly the energy needed to execute the wing’s movements.

The researchers can individually control each of the robotic wing’s movement capabilities, known as kinematic parameters, which enables the team to test the influence of one or more factors, while keeping the other capabilities constant. “We can directly measure the relationship between these kinematic parameters, aerodynamic forces, and energetics,” says Bahlman.

The Brown robotic wing can measure flapping frequency, flapping amplitude, angle of the flap relative to the ground, amount of time used for the downstroke, and extent to which the wings can fold back. That folding motion figured into one set of experiments, where the researchers found the folding of the bat’s wing on an upstroke reduced negative lift and increased net lift of the flapping wings by 50 percent.

Other tests pointed out fragility in the membrane covering the wing’s skeleton, where the leading edge of the membrane frequently tore early on. Bahlman had to reinforce weak spots in the robot’s membrane with plastic threads, which resembled the tendons and muscles at those positions in the wings of real bats.

In the next phase of the research, Bahlman plans to test different materials with the robotic wing. “We’d like to try different wing materials,” says Bahlman, “different amounts of flexibility on the bones, looking to see if there are beneficial tradeoffs in these material properties.”

In the following video, Bahlman and Breuer tell more about and demonstrate the robotic bat wing.

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