Unmanned Systems Technology 036

47 example, while most AUVs are neutrally buoyant, the Flying Nodes can make themselves negatively buoyant when ‘landing’ to ensure they sit firmly on the seabed, and then return to neutral buoyancy for recovery. This capability is achieved through a passive variable-buoyancy system patented by the company, which uses a gas-filled bladder inside each Flying Node that is compressed (becoming less buoyant) as the UUV dives deeper and the ambient water pressure increases. On the upward journey, the water pressure drops, the bladder expands again so its buoyancy rises, and the Flying Node can then surface or attempt a controlled docking with its launch & recovery system (LARS). Also, its wide fuselage, as opposed to the more conventional torpedo- tube shape of many AUVs – and its box wings combined with a pair of shrouded, reversible thrusters inside the wing planform to keep them away from seaweed – enable it to move forwards like a fixed-wing aircraft or backwards in case it needs to extricate itself from anything obstructing its lift-off. Differential thrust allows it to right itself as needed to achieve the optimal trajectory for the upward journey to its LARS. The Flying Node has a wingspan of roughly 600 mm, while the fuselage is 600 mm long and 300 mm tall. It has an overall weight of 35 kg in air, and is depth-rated to 3000 m. To further enable the large number of nodes needed for deployment and placement, the company has also designed them to act in swarms. As standard, they will receive acoustically transmitted updates and high-level commands from a surface vessel while using their own inertial and depth sensors to navigate between position updates. Lengthy trials of the Flying Nodes have been conducted so far, including proving out their autonomy, their ability to land on and take off from the seabed, and their capacity to record and transmit accurate seismic data. The next anticipated steps are to trial multiple vehicles at a time, the goal being commercial operations using thousands of them per ship, stowed in containerised LARSs (similar to ROV garages) to be lowered into and out of the ocean by shipboard davits. James Hedges, CEO of Autonomous Robotics, adds, “We’re also in talks with various parties for using Flying Nodes in environmental surveys and defence monitoring operations in the future. The seismic sensor can be swapped out for any other as applications require.” Marine robotics literature is littered with examples of UUV designers having looked to nature for inspiration, particularly regarding how different aquatic creatures’ shapes and methods of movement help increase their energy efficiency. For example, we reported on EvoLogics’ Poggy and Manta Ray UUVs in UST 30 (February/March 2020), both of which were developed following studies of ray-type fish and how their wings and tails enable them to steer with precision. The company has now unveiled its latest biomimetic design, the PingGuin AUV. As its name indicates, the vehicle’s shape is based on hydrodynamic studies of a penguin, the Adelie species, following trips to the Antarctic and wind tunnel and water tank experiments. From these, it was found that ultra-low drag coefficients could be achieved in water by designing vehicles with spindle- shaped flow bodies that are reminiscent of the shapes penguins adopt when diving and swimming. That has led to the PingGuin being designed with minimal protruding parts that could interrupt the oval shape of its hull, save for four shrouded thrusters UUVs | Insight ROVs used to be the usual tool for placing geophones on the seabed, but our system will be faster and more accurate Unmanned Systems Technology | February/March 2021 The PingGuin is based on the form penguins take when diving into or swimming quickly through water (Courtesy of EvoLogics)