Unmanned Systems Technology 015 | Martin UAV V-Bat | William Sachiti | Sonar Systems | USVs | Desert Aircraft DA150 EFI | SeaCat AUV/ROV | Gimbals

66 team has to close the loop on all manufacturing issues and produce final drawings that are absolutely accurate. In all, the transition from ‘toy’ to industrial product involved major redesigns of the hardware and software, according to Kalwa. To ensure safety at its rated depth of 600 m, for example, the hull was redesigned to withstand the pressure at 900 m and tested to 720 m. The method used to join the modular sections has also been modified, and is now based on that used in torpedoes, while commercial consumer-grade electronics have been replaced by components that meet industrial standards and electromagnetic compatibility (EMC) requirements. The comms system was enhanced with an ultra-short baseline transponder for docking operations and a Teledyne Benthos ELP series underwater locator beacon. On the software front, the company has adapted what it terms a “strict agile” process. That, according to the Manifesto for Agile Software Development (a set of values and principles for an iterative approach to developing software) seeks to make the process more responsive by valuing individuals and interactions over processes and tools. Attention to detail Illustrating the team’s attention to detail, it spent weeks working out how to mould the protective plastic shielding around cable connectors so that it would keep water out under high pressure while allowing the cable to bend. Each cable is pressure tested and issued with a unique serial number so that it can be tracked through the vehicle’s manufacturing process and its service life. The most difficult area of development, Marbach says, was the mechanical aspects of the hull. “That is always the most challenging, because we have pressures of up to 72 bar that we have to design for vehicle going down to 600 m. “We are qualified by the DNVGL, and we have a lot of safety margin in there as well.” He emphasises the effort that went into analysing the structure using finite element modelling (FEM). “We spent many hours on this to optimise it, because we wanted a small vehicle, and small means not wasting too much weight. So the hull needed to be as thin as possible, but also to be impermeable at 600 m.” While some vehicles rely on polymeric materials such as syntactic foams to provide buoyancy and fill voids with a material with good resistance to crushing forces, that has not been Atlas’ approach. “We have not done anything like that because to get as small as possible we needed to have a hull made out of metal, because the foam has density problems,” Marbach says. The foam has a density of around 0.5, half that of water, and that he argues makes a metal hull with air spaces a much more efficient way of creating the necessary buoyancy than foam. “Open-frame designs using foam are always bigger and therefore heavier,” he says. CNC-machined hull The hull structure starts out as a solid billet of aluminium alloy 6 m long. It is then cut into sections and CNC milled to create all the internal structure and spaces for equipment. The SeaCat’s modularity in general, and the SwapHead concept in particular, raises the issues of trim and buoyancy management, which Atlas approached by making each section August/September 2017 | Unmanned Systems Technology The SeaCat has been put through cold- soak tests to temperatures well below the freezing point of fresh water. The darker blue areas here are the coldest Normal vehicles use a lot of neoprene connectors, but they just leak EMC, so we use metal connectors to solve that