56 Digest | Bedrock Ocean AUV Main computer Standard microprocessors serve as the AUV’s low-level control system, while an nVidia Jetson TX2 runs the algorithms for perception and intelligent behaviour, as well as real-time processing of live survey data, and provides significant space for future expansion of data-driven autonomy. “We chose the TX2 as the primary GPU solution that could fit at the time, balancing power, supply chains and a Covid pandemic. We wanted to do high-rate data-processing onboard, because shipping data around has been the biggest challenge in virtually every survey we’ve seen,” Chiau explains. “Moving terabytes of hard drives around the world in FedEx boxes, which get lost, is fundamentally unsound. We knew we had to compute at the edge and do everything we could onboard, which is also how we can get the AUV making intelligent decisions. That feeds into the tailorable behaviours I mentioned earlier: we can get the AUV to track the quality of incoming data to notice and maintain a minimum data spec to quality control the data collected. “Surfacing to beam the raw data via Starlink to a cloud-based processing server isn’t realistic either, and we can’t wait six months to process; we need it in real-time to respond to it in realtime, and that’s what the compute architecture was designed to achieve, at least an order of magnitude faster. Time, data volume and energy are our main constraints to overcome, not the AUV.” One 2 TB SSD is installed on each AUV. Chiau reports that this is more than is necessary per survey, but to maximise value from each morning launch, Bedrock typically carries out multiple mission types per survey day, thus filling up and making better use of the hard-drive space before recovery at day’s end. “We have active onboard data monitoring and can view selected survey lines of data transmitted during surface intervals for GNSS fix to ensure mission success near real time,” he adds. Driven by research While Chiau had previously built battery packs around cylindrical, pouch and prismatic cells, using dry, flooded and oil-filled housings, the pack in its AUV today is made from 18650-type cylindrical, lithium-ion cells (with total energy of 3 kWh) for simplicity’s sake. “We needed something that was reliable enough, and could be bought in batch and flown. We packed them together, used our normal QC and testing processes, as informed by UN 38.3 guidelines, and built a compact and reliable battery pack with multiple redundancies,” Chiau says. “We’re always researching new cells and battery management solutions, but since the pack is made in-house we can change it and scale it at will out of necessity. We never wanted to build batteries, cast antennas or make interconnect systems, but now we can make anything and be fairly self-sufficient – and supply-chain resilient – in critical core technologies.” The pack is split into four independent and hence redundant strings onboard, with a power-management system that routes power from different batteries as needed across the (also redundant) power bus, and several configurations of redundant detection across charging and discharge systems. This ensures tolerance for faults or failures of individual batteries or bus connections to ensure return to surface, and basic mission flythrough in some controlled instances. While Bedrock is satisfied enough with its battery for now, Chiau conversely describes AUV powertrains as “an r&d black hole. You basically choose propellers, brushless electric motors and a motor controller that match the output you’re looking for against the power system and mission requirements. Ours isn’t very different from anyone else’s, the dual-thruster configuration aside. It is fascinating engineering, but it’s a trap, with countless PhD papers on this. It just needs to move enough for the economics.” He concedes that some work went into choosing a motor controller that could output detailed telemetry – around 2000 different operational parameters are recorded onboard, including exact torques of servo shafts, exact motor rpms and currents. Such data is critical for driving Bedrock’s fault detection, isolation and recovery system (FDIR) of logic, maintenance and behaviour algorithms. August/September 2024 | Uncrewed Systems Technology A dorsal fin on the AUV houses a PCB of antennas for GNSS, Iridium, long-range radio and wi-fi
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