Robotic Hummingbird versus Quadrotor: a Flight Dynamics and Gust Response Comparison

The paper discusses an experimental effort aimed at quantifying and comparing the relative flight dynamics and gust response of a two-winged, biomimetic, hover-capable robotic hummingbird (RH) with wing kinematic modulation methods for flight control, against those of a quadrotor (QR) with the same mass, inertias, and motor and battery mass fractions as the robotic hummingbird. Comparing the linear flight dynamics models, the RH model had 2-3x greater translational aerodynamic coefficients along the longitudinal and lateral axes, and rotational aerodynamic coefficients of similar magnitude but opposite sign about these axes. The pitching moment response to longitudinal velocity was similar in the two, while the rolling moment response to lateral velocity was 3.5 x greater in the RH model. Control authority in the longitudinal dynamics was found to be greater in the QR, though this was attributed to mechanism limitations in the RH. The lateral and direction control authority was 1.3 and 4.3 x larger respectively in the RH model. Both vehicles were subjected to a gust in the laboratory. Although the average total movement of the RH was greater than the QR, when the gust speed was non-dimentionalized by the tip speed, the RH had a lesser response. Further, the pitching response was similar between the two, but the rolling response was ? 2 x greater in the RH. Finally, the error between the measured and modeled vehicle responses as a function of wind gust velocity was quantified, which generally increased, especially so for speeds > 5 ft/s. The rotational acceleration equations contained the greatest errors. These results suggest that the linear flight dynamics models are not valid for relatively moderate excursions from hovering flight.