Unmanned Systems Technology 033 l SubSeaSail Gen6 USSV l Servo actuators focus l UAVs insight l Farnborough 2020 update l Transforma XDBOT l Strange Development REVolution l Radio telemetry focus

78 In operation | Seafloor Systems custom HydroCat-150 Lidar was integrated in order for the water department to measure obstacles and potential sources of debris hanging over the water’s surface. As well as selecting an echosounder with the appropriate swathe, Seafloor built a customised version of its HydroCat-150 USV. This version of the catamaran has a dry weight of about 1200 lb (544 kg), measures 4.5 m long and 2.5 m wide, and extends just 0.2 m above the water’s surface. The tallest structure on the vehicle is a mast for mounting the GNSS antennas and the Lidar, giving enough space between them so that they can operate without obstructing or interfering with each other. “The width was considerable, relative to our usual architectures, for reasons of stability,” Tamplin explains. “A little wind is all it takes to make the water’s surface very choppy, so keeping the pontoons about 2.5 m wide apart helps a lot to ensure the echosounder’s coverage can continue uninterrupted without being too affected by splashes or swells. “Also, if the vehicle were to lose power while on the aqueduct, and hurtle towards one of the gates or water- lifting stations, it could both suffer and impart some real damage across the infrastructure,” Tamplin adds. “So we installed redundant motors, generators, batteries, GNSS receivers, everything.” The generators are a unique feature among Seafloor’s USV designs. Having two Honda EU1000i gas inverter- generators ensures a dedicated and redundant power supply to the sensors without drawing power from the battery. As a final precaution, a construct with a series of fabric cords is installed atop the USV, so that in the unlikely event of total loss of control or power, its handlers can either shoot a line across or reach over with a bargepole to catch the vehicle before anything can go awry. Survey preparations Customising a USV to suit the aqueduct project was the biggest challenge for Seafloor. It required input from its specialists in mechanical, marine and robotics engineering to come up with designs – several of which were rejected along the way – and incorporated lessons from previous trials. In preparing for the operation proper, however, Seafloor had to be certain that the USV’s design was based on correct assessments of the aqueduct. Initially, the company requested – and was given – the department’s own blueprints of the aqueduct and its sections, many of which were drawn up in the 1950s and ’60s. Seeing a need for fresh data, Seafloor made two trips to the aqueduct to conduct its own survey. Taking a DJI Mavic Air UAV fitted with an EO camera, it mapped and measured the aqueduct to gauge and validate key points of its geography. “Our investigations showed that there were some parts of the aqueduct where that 20 cm we’ve got above the water would be the absolute limit of how far the USV could safely protrude,” Tamplin says. “If we build a future version, we might look into shaving off one or two more centimetres to be on the safe side.” Furthermore, Seafloor ran SolidWorks simulations of water flows on the USV’s hull, as well as the mechanical stresses, power loads and a range of other mission variables before running the first proving trial. After confirming that the mission could go ahead safely, Seafloor transported the customised HydroCat to the Central Valley of California for the pilot project, a task made easy by the fact that the catamaran had been built to fit directly onto a standard trailer. This set-up also ensured that the USV did not have to be dismantled and reassembled between each survey run. Before the launch, Seafloor was unsure how to safely deploy the USV, as the aqueduct had a concrete liner sloping about 15 m down into the water. However, the water department’s maintenance division provided a boom truck with a crane (typically used for repairs), which has since been used to pick up the HydroCat, lowering it into and hoisting it out of the water. Sailing down the aqueduct The pilot project took in one of the long sections of the aqueduct to prove its performance and viability before official surveys began. Over 12 miles and 6 hours, the obstacles overhead never hung closer than 1 m to the surface, ensuring that the USV’s 0.2 m height was more than enough clearance for safe sailing. “As well as microfractures in the aqueduct walls, we found shifts in the concrete plates at the bottom, and August/September 2020 | Unmanned Systems Technology While sonar was used to inspect infrastructure beneath the water’s surface, Lidar was used to capture structures and potential points of risk above the water (Courtesy of Seafloor Systems)