Issue 39 Unmanned Systems Technology August/September 2021 Maritime Robotics Mariner l Simulation tools focus l MRS MR-10 and MR-20 l UAVs insight l HFE International GenPod l Exotec Skypod l Autopilots focus l Aquaai Mazu

96 operation at Kvaroy each had a tether connected to a topside box for data and power. The end-user had wanted a real- time video feed to constantly monitor fish behaviour, and the team decided at the time that using a tether as a persistent power source was better than using a battery. “However, one thing neither we nor Kvaroy Fiskeoppdrett accounted for at the time was that Arctic storms cause farms to temporarily lose power – their back-up generators take a few minutes to kick in,” Thompson notes. “The first round of robots we built for them had no back-up batteries – no-one thought we’d need them – but during a blackout they’d lose their power source, fall to the bottom of the cage and get stuck in the net. So the Mazu has battery packs to ensure back-up power for recovery during blackouts, as well as upgraded power management systems for a larger sensor payload and more efficient energy consumption.” Given these gains in energy efficiency, redundancy and payload capacity, the Nammu UUVs at Kvaroy island have now been pulled, and at the time of writing the companies were in the process of deploying the more advanced Mazus in their place. The battery pack specifications can vary between missions, although Aquaai generally aims for 250-300 Wh and, whenever possible, slow-charge packs to maximise their lifespan and minimise environmental impact. “If we max out all the devices in the robot – computers, thrusters, servos, lights and so on – immediately after deploying, we’ll exhaust the battery in about an hour,” Pinto adds. “That scenario is not sustainable; we need to use the available energy efficiently and cleverly to maximise the robot’s operating time. On average, our robot can navigate for about 3 hours without needing to recharge. “If you want to extend the work time to its feasible limit, maximising power and energy efficiency, the robot can run for about 8 hours.” The company is also developing a number of underwater charging stations that can be connected to the different kinds of power supplies that might be installed at different job sites. The charging system is expected to be inductive, with a clipping mechanism to ensure that the robot stays in a position where it can be recharged, even in rough weather. A beacon is one of the most probable solutions for docking guidance. Data gathering The sensors on the Mazu can be divided into two groups: navigation and survey. The former of these uses a Doppler velocity log for velocity relative to the seafloor, an altimeter for distance above the seafloor, a GNSS receiver and antenna for position updates when surfacing, a MEMS IMU and a depth sensor. “All this information is fused using extended Kalman filters, and the output is a good estimation for the localisation of the UUV,” says Pinto. “Up to three cameras can be integrated and used for navigation as well as surveys, for example to avoid obstacles such as ropes or wires or to inspect the nets and the movements of fish in farms. “We generally opt for wide-FoV cameras to gather broader sets of information, and because of the murky waters we operate in, it is beneficial to acquire as much information as possible, both for navigation and survey systems. Using cameras designed for low-light August/September 2021 | Unmanned Systems Technology Cameras installed on the front of the Mazu allow for visual inspections and navigation-aiding, and Aquaai is developing computer vision and SLAM to enhance these capabilities Computer vision is great for things like spotting holes in fishing nets, which can allow fish to escape into the wild, or measuring coral biodiversity