A hover-capable insect-inspired flying robot that can remain long in the air has shown its potential use for both confined indoor and outdoor applications to complete assigned tasks. In this letter, we report improvements in the flight endurance of our 15.8 g robot, named KUBeetle-S, using a low-voltage power source. The robot is equipped with a simple but effective control mechanism that can modulate the stroke plane for attitude stabilization and control. Due to the demand for extended flight, we performed a series of experiments on the lift generation and power requirement of the robot with different stroke amplitudes and wing areas. We show that a larger wing with less inboard wing area improves the lift-to-power ratio and produces a peak lift-to-weight ratio of 1.34 at 3.7 V application. Flight tests show that the robot employing the selected wing could hover for 8.8 minutes. Moreover, the robot could perform maneuvers in any direction, fly outdoors, and carry payload, demonstrating its ability to enter the next phase of autonomous flight.

The paper focuses on the design of a robust H-infinity attitude controller for an unmanned small-scale helicopter. To take into account the salient nonlinearities, a model with six-degrees-of-freedom nonlinear dynamics and some linear approximation of the aerodynamic parts are used when extracting a linear model and performing simulations to check the performance of the designed controller. To design a robust H-infinity controller, an augmented plant is constructed by adjusting several weighting functions. Then, a robust controller is synthesized utilizing the augmented system with the weighting functions and H-infinity control methodology. Using computer simulation it is shown that the H-infinity controller works well when applied to the nonlinear model even though it is designed using a linear model approximation. Through frequency response analysis, it is shown that the proposed controller can overcome more than half of the uncertainty variations around a nominal point at the input side. The ti...

In this study, the stable proportional–derivative (PD) controller gains for pitch control (longitudinal control) are obtained using the linearized and non-coupled longitudinal-mode flight dynamics model of the tailless, hover-capable, flapping wing robot named KUBeetle. To acquire a more realistic longitudinal model of KUBeetle, we incorporated the dynamics of the sensors, filters, and servo. Then, the range of PD controller gains that yield stable and sufficient stability robustness are determined using the Routh–Hurwitz, root locus, and H_∞ norm stability analyses. We observed that the stability of the closed loop controller is affected significantly by the dynamics that are incorporated. The PD controller gain with good robustness is selected based on the stability analysis. However, the low frequency gain of the PD controller was too small to attain the setpoint, although the stability margin was sufficiently high. A loop shaping compensator is designed and added to the control loop to improve the low frequency gain while sustaining the stability margin. The frequency and time domain analyses reveal that the proposed control loop can be used for stabilizing KUBeetle. To test the performance experimentally, we implemented the control loop in an onboard control system, which includes a microprocessor and MEMS sensors. The experimental results closely matched the simulation results, demonstrating that the proposed controller could maintain stability in a real system with high flapping noises.

In this work, we report on the structural design of a 5-m-long composite blade intended for use in a horizontal-axis tidal turbine. The blade geometry is constructed through an optimization process to obtain the maximum power coefficient at the desired tip speed ratio of 4.5 by applying the blade element-momentum theory (BEMT). The blade is primarily designed using a NACA 63-424 hydrofoil. The blade structure is designed by using the BEMT to compute the loading conditions at various inflow velocities. Two parallel spars were chosen to produce the blade structure grid, and the preliminary lay-up structure of the composite blade was determined according to the thickness distribution identified using the twisted beam theory under the assumption that the two spars plus the upper and lower skins mostly contribute to the flap-wise bending stiffness while withstanding an external load. Then, high-strength unidirectional and double-bias fiber glass/epoxy materials were chosen to fabricate the blade. The final blade structure was then analyzed in ANSYS Workbench using the finite element method. The results show that the blade structure can withstand the applied load with failure indices <0.4.