Design, Development and Flight-Testing of a Robotic Hummingbird

This paper details the design, development and flight testing of a 62-gram hummingbird-inspired flapping wing micro air vehicle with hovering capability. The key barriers in the development of this vehicle included optimizing the wing design at high flap frequencies by utilizing aeroelastic tailoring to produce the required lift for hover, designing insect-based wing kinematic modulation mechanisms for control and stabilization, utilizing a kinematic autopilot for attitude sensing and vehicle control, and system integration. To achieve the required large flap-stroke amplitudes necessary to generate lift for hover at moderate flap frequencies (∼25Hz), a novel mechanical linkage system called a "modified 5-bar" mechanism was developed, which amplifies the output of a standard 4-bar crank-rocker mechanism. Systematic experimental studies were utilized to design lightweight (∼0.8 grams) flexible wings and to optimize their performance for a specific operational frequency range. Additionally, a fabrication technique was developed, which ensured the wings could be reproduced with consistency. Control of the vehicle is achieved through the use of wing kinematic modulations, which change two key kinematic parameters: the tilt of the flapping planes relative to the vehicle, and the flapping amplitude. This effectively alters the magnitude and direction of the lift vector of each wing to achieve motion or trim equilibrium in a particular direction. Innovative mechanisms were developed to implement this modulation technique, and these mechanisms are controlled via a kinematic autopilot, which senses the vehicle attitude and, using an on-board closed-loop proportional-derivative controller, transmits corrective signals to the servos to stabilize the vehicle. A systematic approach to tuning the vehicle trim and controller gain values has been implemented, leading to several stable controlled flight experiments. One such flight test lasted ∼5.0 seconds in which the vehicle ascended and sustained an altitude of ∼1 meter with minimal drift. The final vehicle weighs 62 grams and flaps at about 22Hz during hover.