28 Alongside the core development of hardware and software, the pair also put considerable effort into advancing their data capabilities, with a particular focus on enhancing the machine-learning algorithms. Every project undertaken enabled them to gather more data, which could then be used to refine and improve the algorithms. “One of the biggest challenges any company faces in performing underwater visual inspections is the scarcity of data; thankfully, we’ve spent much of the past five years diligently collecting underwater data,” Garcia says. System architecture Key constraints influencing the uOne’s internal arrangement and mounting of subsystems are its cylindrical watertight enclosure, EMI and heat dissipation. “Within the cylindrical body, our main CPUs [central processing units] are very close to our IMU [inertial measurement unit]. That isn’t inherently problematic, but then there’s also our powerpack to consider, and all the current running from that to our thrusters, just a couple of centimetres from our magnetometer,” Arteaga says. “We would sometimes have spikes of 150 A, a few centimetres from our navigation sensors. To mitigate that, we’ve optimised the interior architecture such that navigation sensors are at the top of the cylinder, touching the frame, and high-power cables run in the cylinder’s nadir – so the sensors and power cables are as far apart as possible. “On top of that, the high-power wires are EMI-insulated. We validated that setup in various tests and noticed those two measures were enough to ensure our navigation accuracy target,” he adds. Notably, the fourth version of uOne had a separate battery enclosure below the main electronics enclosure. This approach can be seen in some ROV designs, particularly those whose engineers like the passive stabilisation benefits of keeping the centre of gravity (CoG) low. Agile movement In the fifth and final uOne, however, which was designed not for passive stabilisation but equal freedom of movement in all directions, keeping the battery below the main housing would have constricted the AUV’s ability to pitch and roll. Hence the battery is mounted in the middle of the hull. Sacrificing passive stabilisation means the AUV can hold any position and orientation with minimal thrust, power and hence energy consumption, assuming nothing is touching or pulling it (including underwater currents). “The way uOne moves is very unusual and unexpected for any kind of underwater vehicle. Some sensors customised specifically for us just wouldn’t work, because IMUs and DVLs [doppler velocity logs] for the underwater space often have filters that omit readings of our kinds of movements as errors, even though they are precisely what we are trying to pull off – to have the agility of a UAV in an underwater drone,” Arteaga says. The final challenge of heat dissipation was the most troublesome for uOne’s tests and missions in the Mediterranean, where waters can reach 30 C in the summer and cause internal heat to build up to the point where AUV computers and sensors approach their upper temperature limits of about 80 C. Outside such conditions, heat dissipation tends not to present a fundamental problem within the two-hour mission timeframe (with the surrounding ocean otherwise functioning well as a heat sink for the AUV’s acrylic body), but to widen the uOne’s operating envelope, uWare plans to switch from the acrylic hull to an aluminium one in the near future, providing even more thermal conductivity, and hence heat dissipation from hull to water. “We plan on attaching the various computers’ heat sinks to the aluminium frame to cool those through conduction, as water will be flowing near the watertight enclosure,” Arteaga adds. Hull and payload While some commentators have told uWare that the uOne’s hull shape is not hydrodynamic, Arteaga responds: “It’s irrelevant to optimise hydrodynamics at the speeds we move and with the range of movement in different directions we have. If all we wanted was to move forwards fast, we would’ve done the same torpedo shape that almost every AUV has. That philosophy runs throughout the inside and outside of our hull: there is no one perfect solution that is going to solve every problem this AUV weathers.” Instead, the issues prioritised in the structural design include protection, stability and modularity. Protection encompasses everything needed to prevent saltwater corrosion to the February/March 2024 | Uncrewed Systems Technology The outer hull is cast acrylic, but uWare plans to switch to aluminium to enable inspections at greater depths Dossier | uOne
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