Control Laws for Autonomous Landing on Pitching Decks
This thesis addresses the problem of landing a quadcopter onto the pitching deck of a ship, as a partial simulation of a shipboard landing during high seas. The deck is modeled to pitch with a sinusoidal motion. While shipboard landing consists of many stages, only the final landing is simulated in this research. Other ship motions, such as roll and heave, are likewise not considered. The goal is to land the quadcopter in the center of the deck with minimal position and pitch error, where position error measures how far fore or aft of the center of the landing pad the quadcopter lands, and pitch error measures the difference between the pitch of the quadcopter and the pitch of the deck at touchdown. Multiple landing strategies are tested in numerical simulations using Proportional Derivative (PD) and Zero Effort Miss/Zero Effort Velocity (ZEM/ZEV) control techniques. The PD controller is designed to match the pitch of the quadcopter with the pitch of the deck just before landing. The PD controller is shown to be able to reduce the pitch error significantly, but at the cost of position error. The ZEM/ZEV controller is designed to target landing on the ship when the pitch of the deck crosses zero. The ZEM/ZEV controller is shown to be able to land with high accuracy in position and pitch as long as the timing of when the deck would be horizontal was known. A mixture of ZEM/ZEV and PD control is able to land the quadcopter with low pitch and position error even during the presence of timing errors. The simulation results serve to define test conditions for a future experimental validation of the control laws in the FIT ORION Lab.