Date

2021-9-06

Author

Özdoğan, Gökhan

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We propose an unconventional heavy lifting aerial vehicle (HLAV), present the design and its control allocation analysis, and prove the concept by demonstration of the experimental test prototype in the outdoor environment. We aimed for a mechanically robust and simple vehicle design that efficiently performs heavy lifting compared to other common aerial vehicles under certain width constraints, without using a complex swashplate mechanism. The HLAV performs the task of carrying the main load with two large propellers that are efficient thanks to the greater disk area, and includes two small tilting propellers for controllability. This system has a ``PPNN'' (P: Clockwise, N: Counterclockwise) propeller arrangement to compensate for the reaction torques of equally sized propeller pairs placed on opposite sides. However, conventional quadcopters with the ``PPNN'' propeller arrangement lose their controllability upon hovering. Therefore, to ensure controllability, servo motors are integrated into the small propellers giving them the ability to tilt. The nonlinear dynamic model of the HLAV is built by the Newton-Euler approach, and the system is linearized around the hover equilibrium point, for controllability analysis. A control allocation strategy based on quadratic programming is developed to utilize HLAV capacity at maximum performance with optimal power. Model parameters are estimated using closed-loop system identification tools. High-level controllers are designed with the ``loop shaping'' method. Precise positioning of servo motors that are used in tilt mechanism, is a crucial parameter for reducing vibrations in the HLAV and improve overall flight performance. Due to size and weight limitations, the motor is required to be small but torque density is desired to be high. In high torque and inexpensive PMSM and BLDC motors, cogging torque and friction are usually the main challenging disturbance sources. Cogging torque and friction can be identified using position sensors that already exist in the tilt mechanism, so the cost of the system is not increased. We attack this problem by developing feedforward algorithms and show that with cogging torque compensation alone, 30-65% of the positional error can be removed in a feedback control system. The proposed system, HLAV is experimentally tested and verified with a newly designed prototype. Sufficient trajectory tracking performance is achieved in a stable manner and the flight test results are presented.

Subject Keywords

aerial robotics, design optimization, dynamic modeling, control allocation, tilt-rotor, cogging-torque, disturbance rejection

URI

https://hdl.handle.net/11511/93277

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Graduate School of Natural and Applied Sciences, Thesis