Resident AUV design and preliminary testing for autonomous docking and charging at Kilo Nalu observatory

Abstract

Near-shore environments are important to oceanographers because of their relationship to the biogeochemical and anthropogenic processes which occur on land and at sea. Two approaches to researching these environments are undersea infrastructure connected to shore (i.e., cabled observatories) and autonomous underwater vehicles (AUVs). Resident, autonomous underwater vehicles (RAUVs) are a novel way to combine the strengths of undersea infrastructure and AUVs to study the near-shore environment. RAUVs are AUVs which permanently reside at underwater locations and perform multiple missions at a given site of interest without needing physical human intervention. As AUVs, they can capture information at the finer spatial and temporal scales not captured as well by undersea infrastructure, but they can also use said infrastructure to recharge and exchange data over multiple missions. RAUVs used in this manner need to connect to an underwater docking station to charge and exchange data. New, wireless, inductive charging systems show promise for RAUVs over their wired counterparts because wireless systems are less susceptible to damage via seawater corrosion and permit successful RAUV docking after a mission under less stringent positioning tolerances. This research aims to assess the feasibility of RAUV operation in the rough, near-shore environment at Kilo Nalu Observatory (KNO), a near-shore observatory off the south coast of Honolulu, Hawai`i. To that end, I present the design of a low-cost RAUV meant to autonomously dock, charge, and exchange data using KNO’s existing undersea infrastructure. The basis of the vehicle is the BlueROV2 Heavy, an affordable, underwater robot sold by Blue Robotics. Here, I show the mechanical and electrical upgrades made to turn the BlueROV2 Heavy into an RAUV. I also present the work done to develop an internal temperature monitoring system that ensures the RAUV’s batteries do not overheat during charging. I characterize the response speed of our thermistors and verify that the temperature monitoring system works with a simple experiment. Through the work here, I develop an RAUV platform that we can use to test the wireless, inductive charging of RAUV batteries by a docking station and the management of RAUV batteries underwater. In doing so, we move towards creating a RAUV that can one day operate long-term in KNO.