Linear Actuator Equipped Vessel OutperformsFrom October 16 to October 20 of 2014 a team of students and faculty advisors from Florida Atlantic University and Villanova University, called Team WORX, competed in the inaugural Maritime RobotX Challenge held by AUVSI and the ONR. The competitors hailed from five different Pacific Rim nations, and only three teams from each nation represented were selected to compete. There have been multiple publications as a direct result of work on the system, as well as continued research on a graduate level.
The goal of the competition was to build an autonomous surface vessel that is capable of navigating through a complex obstacle course based solely on the integration of computer programming and electronic sensors with a mechanical platform.
The competition itself was comprised of 5 different objectives: navigating through two sets of color coded buoys as quickly as possible, detection of an underwater acoustic pinger, docking in one of three designated slips, detection of a light sequence, and navigation through a buoy field. These obstacles are all created to replicate real life situations that an autonomous vessel should be able to accomplish.
There are several features that allow for the vessel to accomplish its desired mission. The vessel utilizes one of two separate control schemes, depending on its current task. The primary scheme for movement throughout the course is differential thrust; selected for its high degree of maneuverability. The team also decided to incorporate a station keeping controller to better accomplish several of the objectives. This system allows for the vehicle to remain in a fixed position with a fixed heading while floating, as if it were attached to an anchor. This system was mechanically accomplished by attaching two 6 inch Firgelli high speed linear actuators to a clamp on each of the thruster shafts, giving the thrusters the ability to pivot on an axis. This system was show to have a margin of error of <1.5 meters in the x and y axis as well as <2 degrees of heading error. Team Worx was the only team at the competition to utilize an actuated control system, helping them to take 1st place static judging portion of the event.
In keeping true to having maneuverability as a core value for the system, the team decided to have a deployable hydrophone array to execute the acoustics portion of the competition. The array was built in an upside down “T” pattern and utilized ultra-short baseline technology, or “USBL.” The USBL system is capable of determining both location of an acoustic source as well as the depth of that source with a <2 degree margin of error and a range of up to 2000 meters. The hydrophone array was attached to a carbon fiber boom that would deploy when the vehicle determined it was actually necessary. This system was accomplished by a 9 inch FIrgelli linear actuator. The arm of the actuator was placed on the top end of the boom, fitting into a custom built mount. When the actuator was extended, the boom was raised, and when the actuator was retracted, the boom was lowered. This system acquired Team WORX the most points out of any of the vessels systems during competition.
The differential thrust controller, station keeping controller, and USBL system were all designed, built, and tested in house at Florida Atlantic University, as well as other key features of the system.
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