Performance Evaluation of Propulsion Control Techniques for Autonomous Sailboat

Autonomous sailing is a relatively new field of research that has boomed over the recent years. There are several different strategies in literature for autonomous sailboat control, but yet no initiative to compare their performance that we know of. In this paper we propose a methodology for estimating the performance and comparing several propulsion control techniques for autonomous sailboats. Quantitative metrics are extracted from experiments in suitable scenarios to stress the control system. Three criteria are used for evaluation: time to target, energy consumption and safety, resulting in an initial performance estimate for the technique. We also propose an Improved Extremum Seeking technique that smooths the oscillatory behavior of classical Extremum Seeking. Some propulsion control techniques found in the state of the art were implemented in the open-source framework Ardupilot, and experiments in simulation allow for a first performance evaluation of the propulsion system.

I. Introduction

Research in mobile robotics is growing rapidly each year driven mainly by the miniaturization and affordability of digital equipment such as sensors and microprocessors. Whether on land, with humanoid robots or autonomous cars, in the air, with autonomous drones and planes, or by water, with submarines, boats and sailboats, the use of these technologies in field applications is already a reality. Outdoor applications, such as preventing and mitigating natural disasters, collecting environmental data and inspecting large structures, require the robot to operate in a hostile, dynamic and unstructured outdoor environment, where the robot is subject to climatic effects such as rain and wind. Research on robots that operate in aquatic environment mainly focus on two types of platforms: underwater (UAV) and surface vehicles (USV or ASV). These surface water vehicles can be motorized or non-motorized, each more suitable depending on the application [1]. Long-term missions not suited for motorized robots are possible using wind propelled autonomous sailboats. These sailboat robots basically use a sail to transform the force of the wind into their propulsion force, requiring energy only to power the internal systems necessary for autonomy, such as sensors, actuators and onboard computers. Autonomous sailboats are favored in tasks that require a higher level of persistence where energy self- sufficiency is desired, such as coastal surveillance and ocean data collection [2].