Issue 37 Unmanned Systems Technology April/May 2021 Einride next-gen Pod l Battery technology l Dive Technologies AUV-Kit l UGVs insight l Vanguard EFI/ETC vee twins l Icarus Swarms l Transponders l Sonobot 5 l IDEX 2021 report

87 tools and the use of manned boats,” Tietz says. “To that end, the Sonobots 2 through 5 have been designed for streamlined surveys of rivers, lakes and other shallow waters.” Dr Ilja Lange, head of underwater robotics development, adds, “We had many targets we wanted to achieve with the Sonobot 5, but after initial examinations and discussions we found we really had to take a lot of its key design aspects back to a blank sheet. “For example, our thrust was limited by the diameter of the jet channel in the propulsion system and the susceptibility of its inlets to seaweed blockages, and we also wanted to replace our connectors to reduce vulnerabilities to salt water during disassembly. “We wanted to reduce the number of parts and institute a few other changes as well, which is why we had to rethink our architecture from the ground up.” These development targets and the engineering performed to achieve them have resulted in a foldable USV with no external connectors, weighing a maximum of 27 kg, with a length of 1300 mm, a width of 920 mm, a height of 805 mm and a draft of 120 mm – just large enough for high-end professional mission requirements yet small enough to be handled by a single operator. “We also completely redesigned the internal electronics, including a new PC architecture to replace the COTS system we’d used previously, which had often presented issues with interfacing, power management and so on,” Dr Lange says. “So we designed our own system on a high-power, scalable four-core PC in a compact ‘brick’ form factor. “As well as having an eight-channel power board for carefully monitoring and controlling the power consumption throughout the Sonobot, this allows us to add the latest systems through interfaces such as serial, Ethernet, I 2 C and others, as is necessary for any kind of payload users will need in the future.” The flexibility and intelligent diagnostics allowed with this new PC form part of future-proofing the Sonobot 5’s subsystems. Each aspect of its technology has reached a level of maturity and modularity that is consistent with the company’s move towards serial production of the USV. Propulsion The Sonobot’s power comes from a purpose-built battery, assembled in- house and consisting of two 529 Wh modules, each with seven lithium-ion cells connected in series. That gives an endurance of 9-10 hours at survey speeds, although the company notes that users can achieve up to 15 hours at 1 m/s if there are no disturbances, with battery swaps taking less than a minute. The modules are fitted in the USV’s floats on either side of the central body to keep the centre of mass low and enable easy heat dissipation to the water. A COTS BMS monitors temperature, voltage, current and a few other parameters. Its propulsion system runs on two motor-propeller drives installed in the two floats. As Dr Lange says, “We have used jet thrusters since the Sonobot 3, inlaying them in carbon tube hulls to avoid the problems many USVs experience from having open propellers. “We wouldn’t get clogging from debris or vegetation, we didn’t need to worry about propeller blades breaking off as a result of impacts with rocks, and we avoided the large draft requirements that boats with outboard motors need, making it easier for the Sonobot to survey shallow waters.” He also notes that hydrographic surveyors are occasionally prone to treating their USVs and ancillary equipment a bit roughly – it is not uncommon for them to throw the vehicles into the water or in the backs of trucks – so designing a robust propulsion system without easily broken parts was key. “Our main issue with the Sonobot 3’s thruster arrangement however was the small diameter of the jet channel, which limited its power output and cost it efficiency at higher speeds,” he says. “There were also a few other, smaller problems; for example, the grille on the jets’ inlets was prone to becoming blocked by seaweed. “We knew that propellers would gain efficiency with larger blade diameters, but we didn’t want to integrate props EvoLogics Sonobot 5 | Digest Unmanned Systems Technology | April/May 2021 The Sonobot 5’s batteries are stored in its floats, for a low centre of mass and easy heat dissipation