21.7 Sunday, Jan. 4 15:00 Passive wing morphing as a consequence of centrifugal acceleration in flapping wings STOWERS, AK*; LENTINK, D; Stanford University; Stanford University email@example.com
Birds, bats and insects are able to maneuver in cluttered environments that are practically impossible for flying robots to navigate. In these situations, animals are able to morph their wings in complex manners to avoid collision or damage. From dynamic analysis and robotic experiments, we predict that the combination of flapping wings and a wrist joint may aid in the wing’s recovery from obstacle impact. During flapping flight, centrifugal accelerations drive wings to unfold to their full wingspan without requiring use of muscles and tendons. This enables wingspan recovery using minimal effort. We demonstrate this effect in a 40 cm wingspan robot flapping in the range of 5-17 Hz. The robot has two flapping wings and is constructed with an unactuated joint at the wrist allowing the wings to passively adjust sweep angle in response to disturbances. Experiments show that following impacts, or after release from being held shut, the flapping wing will passively unfold within one to two flaps. A model based off the inertial properties of the wing during flapping predicts this unfolding is caused by centrifugal acceleration of the hand wing. For the wing amplitudes and fold ratios of bird, bat and insect wings, our model predicts that their wings can recover passively from impact in approximately one half to one full wingbeat.