58 “But we’ve not had time to optimise the powertrain until now. Short of winding our own stators, we just bought COTS units that did 80% of what we wanted,” Chiau says. “Now we’re at a place where we want higher reliability and much higher performance. We want to spin bigger props, more torque, lower rpm, but also speed to unlock harsher environmental operating envelopes. You can’t just equip some new motor controller to get all that; you have to match a propeller to a motor to a motor controller, and then that will drive the battery design to match the loads and interfaces across the architecture. It will mean holistic transformation of the propulsion section while still retaining high-level parameters and lessons for smooth operation and buoyancy.” Wireless connectivity Most AUVs today feature a dorsal pod or mast with antennas for comms and GNSS when surfaced, and significant customisation went into Bedrock’s model as it could not find a COTS solution with the right antenna count, depth rating and form factor. The latter point was important, as many off-the-shelf submersible antenna masts would have made the 60 kg AUV cumbersomely bulky. “Instead, we made ours resemble a fin atop the AUV. Inside that are all of our antennas etched on a PCB,” Chiau says. “Custom patch elements covering GNSS, iridium, long-range radio and wi-fi, while also carrying NAV lights, status indicators and emergency strobes, both visible and IR. The individual radio and GNSS chips are standard COTS parts, including a u-blox GNSS receiver, which we can PPP (Precise Point Positioning) process for added accuracy post-mission.” Additionally, an acoustic modem integrates with the USBL system as a recovery assistance and communication device. Integrating its own GPS receiver and antenna, it can pull inertial data from the dry compute section to ping out a packet of location data for end-users to recover. The power-management system prioritises its power distribution such that this pinger remains active even if most other systems fail – it actually “fails on”, as Chiau puts it. SLA-printed hull Bedrock assembles its pressure housings in-house from two aluminium endcaps bonded either side of composite tubes. Aluminium heat sinking is built-in throughout the design (in the end-caps and elsewhere) to compensate for the composite’s lower thermal conductivity, and take advantage of the water heat-sink flooding elsewhere in the vehicle body. The AUV’s internal structure is aluminium, while the outer fairings are printed via large additive manufacturing (AM) via stereolithography (SLA), with syntactic foam placements at the midsection for flotation. AM appealed to Bedrock for its rapidity and how it enables easy adjustment of the vehicle body, compared with fibreglass manufacturing. “There was a lot of early hydrodynamics testing, and we frequently wanted to change fins, control surfaces, and just the whole outer shape,” Chiau notes. “That was for improving internal packaging space, aesthetics and impact tolerance. On that latter point, you’ll see a structural ring in the front of the vehicle, always farthest ahead, because that is the first thing we want to weather an impact, and it’s mechanically linked to the robust, aluminium skeleton, which can handle hard bumps easily. It also provides the primary load path for launch and recovery latching.” In SLA, a bath of resin is fused into solid layers of printed structural patterns by UV lasers, which cause the resin’s monomers and oligomers to cross-link and form polymers, higher and higher over time until the uploaded CAD structure is complete. While prized for the intricate detail it can achieve, SLA’s specific appeal to Bedrock came more from an undisclosed material it enabled them to use, which matched ABS (acrylonitrile butadiene styrene) for impact resistance, acoustic transparency and other missioncritical qualities. Bedrock anticipates potentially switching to thermoplastic moulding machines or other mass-production August/September 2024 | Uncrewed Systems Technology With BVLOS operations already achieved, Bedrock will target automated BVLOS launch and recovery in its next engineering ventures
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