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

95 Pieterkosky says. “And each printed part is encased in either an epoxy liner for added strength or a buoyancy material.” Before settling on Neoprene, Aquaai had also tested silicone and some other plastics to identify how best to achieve the environmental ruggedness and ‘exoskeleton-swimming’ capability it sought. Pieterkosky notes here his background in animatronics, as a key part of engineering realistic robotic creatures was close simulation of the vertebrae to be emulated. “Traditional plastics will break if they hit a rock or tree branch, but if we create a mechanical frame that can bend inwards flexibly – as fish vertebrae do – we protect not just the robot’s mechanisms but the outer Neoprene skin too,” he says. “Flexibility is key to absorbing and spreading the force of impacts rather than keeping them concentrated at a single, brittle point like on regular UUV hulls.” The pH levels of operating environments must also be considered. In a chlorinated pool, Neoprene will last about 3 months; in saltwater, far longer. For example, the Nammu has been tested in saltwater over 2 years without its skin breaking. As a final point, Neoprene is 80% recyclable. Power and locomotion Flexibility is also key to the Mazu’s motion; it uses servo actuators (‘clothed’ in the Neoprene) to produce a flapping motion along the body to propel the system forwards. Two of the actuators are at the back (in the tail), which work in sync as a primary forward thruster and to help the vehicle bend as needed for propulsion and impact mitigation. Much like the work of Animal Dynamics (see UST 34, October/ November 2020), Pieterkosky spent four years researching the advantages of different fish swimming patterns before assembling the first prototype. “For example, clownfish are sluggish when they move, but they can absorb impacts against coral really well, while tuna can swim in long stretches while using very little energy,” he says. “We’ve designed the Mazu to drift more than swim. We’ve emulated the way salmon and carp move in rivers, or clownfish around coral, to successfully drift with currents using the water to stabilise us, and not take damage from underwater ‘gusts’ or impacts. “Fitting the system architecture into the right displacement is critical to getting that drift right. We can accommodate somewhere between 60 and 100 kg of sensors on board: the bottleneck isn’t so much their weight or power but their volume, and how much we can move our electronics around to get the right hull size and shape.” Lead robotics engineer Filipe Cerveira Pinto says, “It’s much more power- efficient to move that way. Not only do we avoid using relatively power-inefficient conventional thrusters, we also use the kinetic energy of the streams from rivers or schools of fish to provide some of the Mazu’s propulsion in place of our own battery energy. “It really helps us operate for hours at a time between recoveries and recharges. With small adjustments in the angle of the tail, we are able to navigate over long distances without expending much energy. That allows a significant increase in how long the robot can operate before it has to recharge. Pieterkosky adds, “Conventional, torpedo-shaped AUVs have a huge turning radius, consuming a lot of energy to change direction, but the Mazu and its past iterations can turn on a dime. We could do close-up camera inspections of canal walls less than 2 m wide, for example. “Also, we swim as slowly as possible to capture really accurate data. Surveying isn’t racing, and speed leads to poor visual, acoustic and environmental data, but if we wanted to, we could reach 5 knots at maximum thrust.” Further servos are used along the length of the robot to achieve the desired flexibility and motion. Aquaai declines to explain the full actuation architecture, to protect its IP, but notes that the total number must be tempered to reduce manufacturing cost and potential points of failure. Energy management The power architecture has evolved over the robot’s iterations to suit customer needs and environments. While the first prototype was battery- powered, the Nammu UUVs in Unmanned Systems Technology | August/September 2021 The Mazu’s sonde can incorporate up to 12 environmental sensors for tracking water parameters such as pH, salinity and levels of oxygen or chlorophyll