In recent years, various fields have shown increasing amounts of interest in the use of UAVs due to their versatile characteristics and wide range of application possibilities. To increase flight time and battery payload capacity, but still maintain compact size and high maneuverability, there have been efforts to increase the size of the propellers and placing them closer together. This leads to flow interference force between rotors and consequently a loss in exerted thrust.
This thesis simplifies the general UAV system into a linear 1D problem and focuses on one propeller, where a force sensor is placed between the load and the rotor. The force sensor measurement differs from the actual exerted motor thrust by a constant unknown bias force. A state space model is constructed of this system to analyse the dynamics of the propeller. A study on the observability of the system is done to find a minimum set of measurements that results in full reconstruction of the state. By including the unknown bias force and applied rotor force into the state, these values can also be estimated by designing an observer.
After verifying the observer through simulations, an additional goal is to enable the load to follow a desired trajectory. The actual states are unknown, therefore estimated states are used for a state feedback controller to ensure system stability. Besides, feedforward control is implemented to make the load able to follow non-constant reference trajectories. The performance of both controllers could be shown through simulations with step and sinusoidal reference signals.