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

80 a grand total of 13 cars that had been dumped or driven into the waterway over the years,” Tamplin notes. “Also, the projected power curves and other data we’d gathered from our CAD simulations matched up almost perfectly with what happened in the pilot project. Going in, I was sceptical about how much – or, more precisely, how little – power the operation would need, but the amount of battery power worked out surprisingly well.” With no incidents and around 1 Tbyte of survey data gathered, the pilot was deemed a success, and the department took the USV to begin carrying out similar surveys on the remaining sections of the aqueduct. It carried out the bulk of operations, with Seafloor providing a few technicians for on- site consulting during the earlier legs. Because the current in the aqueduct varies depending on the flow of water, there is a risk that the speed and handling of the USV could vary, which could have reduced the accuracy of the surveys. To help stabilise this load – and by extension the point cloud data from the echosounder and Lidar – the department typically closes nearby water gates upstream, which reduces the current to between 1 and 2 knots. “To provide even further stability for gathering data in that current, we designed this USV with skid-steer functionality,” Tamplin says. “Essentially we’ve put in two fixed thrusters, which are used in a differential steering mode that keeps the vehicle in the centreline down the aqueduct, and moving at about 2-3 knots.” In addition, the T50 operates at a beam width of 0.5 x 0.5 º , with 1024 beams across the swathe. This is to enable imaging of very small cracks, as well as compensating for the strong reverberations coming from the aqueduct’s concrete walls. And as the standard swathe of the sonar reaches much farther than the boundaries of the aqueduct, in actual operations the survey team can reduce the T50’s power consumption. By how much varies between different sections, but in general the 400 W sonar (200 W per head) is operated at an average of 350 W. “The survey team can also turn down the power on the IMU and other systems through a PC interface to save on main battery power,” Tamplin adds. “That said, we installed almost 880,000 mAh of battery capacity on the catamaran, because we were worried about endurance. But because it’s travelling downstream at such a gentle speed, the vehicle pretty much always has quite a lot of leftover endurance at the end of each survey leg.” Further to this, the water department wanted not only to survey for cracks and debris beneath the water but for structures, walkways and other potential sources of debris falling onto the surface. “That’s why we installed that Carlson Merlin Lidar in the vehicle, to simultaneously map below and above the water,” Tamplin says. “We’d already picked the echosounder and the IMU, and we chose this unit because all the other high-end Lidars we were using already came with their own internal IMUs. “We didn’t need one of those though, because the Applanix POS MV IMU that came installed on the echosounder was more than good enough for navigation and geo-tagging all the incoming point August/September 2020 | Unmanned Systems Technology GNSS-IMU: Applanix Corporation Wi-fi datalink: MikroTik Generators: Honda Sonar: Teledyne Reson Lidar: Carlson Electric motors: Torqeedo Batteries: Torqeedo Some key suppliers The water department provides a crane truck for lowering the USV into the water and recovering it between sections of the aqueduct (Courtesy of Seafloor Systems)