| The agility and miniature size of nature's flapping wing fliers has long baffled researchers, inspiring biological studies, aerodynamic simulations, and attempts to engineer their robotic replicas. Flapping wing flight is characterized by complex reciprocating wing kinematics, transient aerodynamic effects, and very small body lengths. These characteristics render robotic flapping wing aerial vehicles ideal for surveillance and defense applications, search and rescue missions, and environment monitoring, where their ability to hover and high maneuverability is immensely beneficial.;One of the many difficulties in creating flapping wing based miniature robotic aerial vehicles lies in generating a proper wing trajectory that would result in sufficient lift forces for hovering and maneuvering. Since design of a flapping wing system is a balance between overall weight and the number of actuated inputs, we take the approach of having minimal controlled inputs, allowing passive behavior wherever possible. Hence, we propose a completely passive wing pitch reversal design that relies on wing inertial dynamics, an elastic energy storage mechanism, and low Reynolds number aerodynamic effects. Theoretical models, compiling previous research on piezoelectric actuators, four-bar transmissions, and aerodynamics effects, are developed and used as basis for a complete numerical simulation. Limitations of the model are discussed in comparison to experimental results obtained from a working prototype of the proposed passive pitch reversal flapping wing mechanism. Given that the mechanism is under-actuated, methods to control lift force generation by actively varying system parameters are proposed, discussed, and tested experimentally.;A dual wing aerial platform is developed based on the passive pitch reversal wing concept. Design considerations are presented, favoring controllability and structural rigidity of the final platform. Finite element analysis and experimental characterization is performed on the proposed design, yielding acceptable coupling and rigidity characteristics. A working prototype is manufactured from carbon composites and characterized for its lift production capabilities. A scaling law based on momentum flow theory and design scaling arguments is developed, predicting an increase of lift-to-weight ratio of the robot with decreasing size. Per the theoretical considerations, a scaled down prototype of the robot is manufactured and experimentally characterized. System geometry and parameters were optimized based on the developed full system theoretical model to yield maximum lift force. Finally, preliminary control is attempted on the flapping platform employing a decoupled methodology for the roll and pitch direction. A simple Proportional Integral Derivative controller is implemented on the experimental prototype mounted on a motion constraining rig, yielding acceptable trajectory tracking characteristics. |
