Design and Evaluation of a Fixed-Pitch Multirotor UAV with a Nonlinear Control Strategy

The use and practical applications of small UAV systems has continually grown in the past several years in both the public and private sectors. These UAV systems are used for not only defensive purposes, but for commercial applications such as exterior bridge and home inspections, wildlife/wildfire management and observation, conservation exercises, law-enforcement, radio-repeating operations, and a wide variety of other uses that may not warrant the use, expense, space constraints, or risk of a manned aircraft. This thesis focuses on the design of a fixed pitch multirotor UAV system for use in furthering research projects and facilitating payload data collection from a flying platform without the expense or risk of testing with available larger UAV systems.

The design of a multirotor UAV system with a flight control scheme, communication architecture and hardware, electrical architecture and hardware, and mechanical design is presented. An Extended Kalman Filter (EKF) strategy is implemented aboard a developed Inertial Measurement Unit (IMU) to estimate vehicle state. Experiments then validated the estimates from the EKF through a comparative approach between the developed unit and a commercial unit. A nonlinear flight control system is implemented based on an Integral-Backstepping control strategy. The flight control strategy was then fully simulated and exhaustively tested under a variety of external disturbances and initial conditions from a fully dynamic modeled environment. Parameters about the vehicle were experimentally determined to increase the accuracy of the model which would increase the chances of successful flight operations.

Flight demonstrations were conducted to evaluate the abilities and performance of the control system, along with testing the interface abilities and reliability between a universal ground control station (UGCS) and the aircraft. Lastly, the model was revisited with the input data from the flight control experiment and the output captured was evaluated against the output of the model system to evaluate effectiveness, reliability, and accuracy of the model. The results of the comparison showed that the computer simulation was accurate in predicting attitude and altitude of the vehicle to that of the realized system.