Unmanned Systems Technology 016 | Hydromea Vertex AUV | Power management systems | Unmanned Space Vehicles | Continental CD-155 turbodiesel | Swift 020 UAV | ECUs | DSEI 2017 Show report

October/November 2017 | Unmanned Systems Technology 22 Dossier | Hydromea Vertex AUV That is changing, however, as more and more highly integrated solutions come onto the market, he says, citing very small multi-parameter sondes with small sensor units, such as the modified EXO 2 that Hydromea chose for the Vertex. “We really designed the vehicle around the EXO 2, and if in a few years sensors get even smaller then potentially we could miniaturise it further,” he says. Another reason to develop so much of the vehicle in-house, Schill explains, was cost control. “If you buy commercial off-the-shelf units for everything – for your navigation solution, thrusters, pressure hull and so on – they are often way too big for what we want them to do, and also way too expensive if we want to scale up production. “Now we control the whole ecosystem, the whole vehicle stack, and if we want to ramp up the numbers to make 20, 50 or 100 vehicles then we can see some economies of scale.” Structure Physically, the heart of the vehicle is a cylindrical pressure hull consisting of a tube with end caps, all made of an undisclosed monolithic plastic. This contains the battery pack, which occupies almost two-thirds of its volume; the electronics stack consisting of multiple circular printed circuit boards (PCBs), which Hydromea designed and populated with electronic components; and the ‘dry’ end of the payload, principally its data logging functionality. The battery pack and PCBs are all bolted through a supporting frame to one of the end caps so that, once the first end cap has been removed, the cylinder can be pulled off to expose everything for maintenance or modification. With a modest operating depth and a small internal volume, the pressure hull is not highly stressed, which permits construction from a relatively inexpensive material. All the subsystems require waterproof access through the pressure hull for connectors, which are in the end caps. All the connectors required for the basic vehicle systems are grouped on the rear end cap, leaving the front cap for connectors and mounting points dedicated to the payload. With the moderate water pressures encountered at 300 m, there was no need to minimise the number of access points, which would be a big issue at greater depths to ensure structural integrity. However, Hydromea powers and controls the Vertex’s five electric thrusters through one connector, the signal cabling being minimised by connecting the thrusters to the vehicle’s CAN bus. Enveloping the dry pressure hull is the wet outer hull, which is made from moulded and painted syntactic foam. This is a shell that supports the motor/thruster modules at the rear and the sides, the acoustic transducers, the comms antennas plus the connection for an optional data tether, and also houses the wet end of the sensor payload at the front. The outer hull structure has been simplified as the design has evolved. “It’s a work in progress, something where we are iterating,” Bahr says. “The important thing is that we need extra buoyancy from the hull, otherwise we could either not keep it this small or we would have to sacrifice battery The operational concept for the Vertex involves groups of ten or 20 vehicles, communicating and localising through onboard sensors (Courtesy of Hydromea) The Vertex carries its water-sampling sensors in the nose, their wet ends protected by a 3D-printed polymer guard (Photo by the author)