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

67 SeaCat AUV/ROV | Digest neutrally buoyant in its own right. That means, for example, that the thruster sections can be removed for some configurations without affecting the vehicle’s buoyancy or trim. “There is a lot of weight management, and with that there is a lot of mechanical FEM analysis involved,” says Marbach. This approach also saves time and effort on the factory floor because workers can concentrate on building vehicles rather than spending hours trimming them once they are complete, he says, adding that Atlas wants to build an off-the-shelf product, delivering the same SeaCat every time that simply works as advertised when the parts are put together. While buoyancy and trim don’t change when different modules are combined, length and mass do – factors that affect how the vehicle responds to control inputs. An important factor in achieving that is the recognition system that tells the controller which sections and SwapHeads are attached, and adapts its control scheme accordingly. The SwapHead concept uses a standard interface that includes mechanical locking devices and waterproof seals, along with Ethernet and RS-232 plugs and the ‘backseat driver’ interface that allows the payload to control the vehicle. “For example, we have a SwapHead that turns 360° with a camera mounted on the side so you can look at a wall next to you,” Marbach says. “The head has a stereo camera that sees the wall and directs itself to the wall, and at the same time it steers the vehicle to where it wants to go.” That has to be tightly integrated because the sensors need very high navigation and positioning accuracy. The most demanding, Marbach says, is a new synthetic aperture sonar (SAS) option, with the MBES coming a close second. “The multi-beam is pretty demanding. Because we fulfil the ISO S-44 standard with the vehicle we need to be very accurate,” he says. While the geomagnetic SwapHead is in its normal position at the front, the magnetometer itself is towed 3 m behind the SeaCat to ensure it is clear of the AUV’s own magnetic signature. “It has a small signature – we are amagnetic – so we are good for mine hunting, and we fulfil the Stanag 1364 mine warfare requirements,” Marbach says. Electromagnetic compatibility As an off-the-shelf product, Atlas has put a lot of effort into ensuring the SeaCat complies with key international standards, including DNV GL 1-5-3 covering unmanned submersibles, the same organisation’s BV 0430 for shock and BV 0240 for vibration, the US Mil-Std 810G for resistance to environmental effects along with Mil-Std 461 F for EMC. Marbach says meeting EMC standards was challenging and involved a lot of work on connectors and electric motors. “Normal vehicles use a lot of neoprene connectors,” he adds, “which we try to avoid because they just leak EMC. We use metal shell connectors to solve the problem.” The main EMC risk to an underwater vehicle comes when it is being prepared on the deck of a ship, and potentially exposed to powerful emitters including radars and comms radios. The SeaCat has also recently achieved compliance with the UN38.3 regulation governing the transport of dangerous goods, allowing the vehicle to be carried on aircraft, for example, without having to remove the lithium-polymer battery. Another must for an off-the-shelf, turnkey product is a comprehensive range of optional ancillary equipment, which Atlas has organised into support sets. These include a control set based on a rugged laptop, a base station for the acoustic modem, a remote control unit for surface manoeuvring and a mission data processing software suite. Future directions Future developments include the SAS mentioned above, which Atlas is developing with an undisclosed partner. Incorporating it will require the use of a new 1.2 m modular hull section that will result in the longest configuration so far for the SeaCat. Atlas also continues to refine the control software to enhance the SeaCat’s autonomous capabilities, such as on-the- fly mission re-planning to compensate for currents, so that it can continue to run a ‘lawnmower’ survey pattern and complete its mission within its energy budget. For example, if one rudder fails then the controller will try to keep it on the route and not simply decide to go home. As a hybrid AUV/ROV, the SeaCat can combine the capabilities of these two distinct vehicle categories, marking an important trend in the technology. Unmanned Systems Technology | August/September 2017 The trolley is part of a suite of support equipment developed for the SeaCat that ranges from control handsets and toolboxes to a containerised mission control station