Dynamics and Control of Flexible Quadrotor Aircraft
Open Access
- Author:
- Smith, Christopher
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 18, 2023
- Committee Members:
- Robert Kunz, Professor in Charge/Director of Graduate Studies
Alok Sinha, Chair & Dissertation Advisor
John Cimbala, Major Field Member
Simon Miller, Outside Unit & Field Member
Alfred Lewis, Major Field Member - Keywords:
- Quadrotor
Flexible Structure
Optimal Sliding Gaussian
Flight Control
Flight Simulation - Abstract:
- Quadrotor UAV configurations have been used with great success throughout industry and show potential for scaling to larger sizes suitable for high payload capacities, including passengers. As the size increases, the flexible properties of the structure can influence the flight dynamics of the system. Contained in this work is a detailed derivation of the equations of motion for a notional quadrotor with a flexible structure. The beams connecting the motors to the central control unit are flexible in three degrees of freedom: vertical bending, horizontal bending and torsion. Natural frequencies of simplified systems have been computed, and a simple proportional-derivative (PD) controller is designed and simulated assuming a rigid frame. This baseline controller is exercised in the flexible system, and results in poor flight performance. A robust Optimal Sliding Gaussian (OSG) control scheme is designed using a rigid linear model to be robust to the unmodeled flexible dynamics. The OSG controller is demonstrated in a six-degree-of-freedom flight simulation which includes non-linear aerodynamics due to dynamic stall of the rotor blades during forward flight. The OSG controller is able to achieve stable, controlled, flight where the baseline PD controller failed. Additionally, exploitation of the torsional flexibility of the connecting beams to increase the available control authority in the horizontal plane is explored. An OSG control scheme is designed and tested in a linear rigid simulation and a nonlinear flight simulation to demonstrate the utility of the new control authority. The linear and nonlinear flight simulations show that horizontal motion without the use of overall vehicle tilt is possible by twisting of the quadrotor frame members.