An electromagnet-operated descent weight mechanism designed for a hovering AUV

The National Institute for Undersea Science and Technology (NIUST) operates a hovering AUV, Mola Mola. This vehicle is a SeaBED class AUV initially designed at Woods Hole Oceanographic Institution with hardware and software refinements performed in-house at the NIUST AUV Lab. The primary function of Mola Mola is to perform photo surveys at an altitude of 3 meters from the seafloor. Dives performed at depths less than 400 meters have been made with little positional drift using the vehicle's vertical thruster for descent propulsion. Deeper dives in the vicinity of 600 meters have suffered much greater navigational error due to descent time and positional drift due to currents. A descent weight mechanism was designed for the vehicle to reduce the time and energy expended during the the dive and transit to the survey area. An electromagnet was used to retain the weight so that it would be released in the case of a power failure. The system was field tested in April of 2012 during engineering trials in the Gulf of Mexico.