Methods for stabilizing the longitudinal dynamics of a biomimetic robotic hummingbird in hovering flight

Hummingbirds and many flying biological organisms use a method known as wing kinematics modulation (WKM) for flight control and stability. This technique involves actively varying the wing flapping kinematics during flight to generate control forces and moments in response to desired trajectories, external perturbations, and natural instabilities. Recently, we designed, developed, and free-flight tested a biomimetic robotic hummingbird which uses these methods for flight control. For longitudinal control, two methods were implemented: (1) flap plane tilting which generates a coupled pitching moment and horizontal force, and (2) wing stroke mean shifting, which moves the longitudinal position of the aerodynamic center relative to the center of gravity, generating a pure pitching moment. The robot was flight tested in hover using each of these control methods. The first method resulted in higher translational velocities, larger attitude angles, and higher pitch rates, as well as off-axis roll and yaw rates. The second method resulted in significantly less movement. These results suggest that the plane tilting method is best for introducing larger changes in states, while the mean shifting method is best for more precise hovering. This is the first experimental study to quantify the effects of biological flight control strategies on the hovering flight of a two-winged, free-flying robotic hummingbird. These results could be used to inform roboticist on the best methods to use for controlling the longitudinal dynamics of flapping wing robots, as well as derive control schemes that leverage the two methods for quick and efficient execution of flight maneuvers.