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

25 Hydromea Vertex AUV | Dossier While the Vertex is rated to 300 m, the thrusters can be used on vehicles that go much deeper: Hydromea quotes a depth rating of 6000 m. “A lot of development went into the thrusters, which the company makes from basic materials such as copper, magnets and plastic. We make them in-house at the moment, but we have plans to outsource their manufacture eventually,” Schill says. Control of the electronics stack The electronics stack was another major in-house development, according to Bahr, who summarises its key functions as controlling the vehicle and turning things on and off to manage power demand. “It has a navigation engine interfaced with a payload interfaced with the thrusters. That is of course our circuitry.” As well as designing the PCBs and getting them made, Schill emphasises that they wrote all the software too. “For miniaturisation and also because we want to build a swarm system, it is important that we have full access to the software stack,” he says. If you buy an off-the-shelf subsystem, it might contain information that other parts of the system need, but the manufacturer might not allow access to it. As he explains, “If you have access to everything, you can often exploit synergies so that you measure a parameter once and then share it among all the other units.” Full control of the electronics and the software also makes it easier to make changes if, for example, a smarter way of doing something is found that requires changes to the physical electronics, the signal and the software. It also helps to save space, says Bahr, as custom-designed boards minimise the number of modules that have to be interconnected. “What you need is on your board, and what you don’t is not.” Doing things this way also minimises the amount of cabling required. Apart from one, ten-wire ribbon cable there is no wiring loom as such in the vehicle, and nothing that has to be soldered. The amount of overhead this approach can save is significant. Schill says, “If you buy things that come in housings and have connectors, that makes everything quite big. If you want to miniaturise them you’ve got to get several functions onto the same PCB, or maybe use very densely coupled modules that are closely plugged together.” It also affects power consumption he says, enabling the designers to minimise the ‘hotel load’, which is the power required to run basic vehicle systems excluding propulsion. “Without the motors, but with the sensors on, the hotel load is about 2 W, which is much less than on many other vehicles,” he says. Battery issues The cylindrical battery pack uses readily available 14.4 V lithium-ion batteries with a total capacity of 160 Wh that provide a maximum endurance of between six and eight hours and a top speed of 1.5 m/s. However, because of the air transport restrictions placed on lithium-ion batteries, Hydromea offers a drop-in replacement that uses nickel metal hydride batteries, to which no such restrictions apply but which halves the endurance. Comms and localisation Vertex’s underwater comms and localisation functions depend on a general-purpose acoustic transceiver system also developed by Hydromea. They designed it from scratch including the electronics, the software, the mechanical integration with the transducers and mouldings for its housing. “For the initial prototypes and the first production units it’s all in-house, and again we are looking for manufacturers who can make them in larger numbers,” Schill says. The system draws on bodies of theory to which Bahr and Schill’s PhD work has made a contribution, Bahr in localisation and Schill in comms. The idea is that vehicles in a group that know roughly where they are individually in the water can improve the accuracy of that knowledge if they share the information with other members of the group. “That is basically the underlying Unmanned Systems Technology | October/November 2017 Each Disc Drive Thruster is hubless and driven from the rim by its own integral electric motor and motor controller (Courtesy of Hydromea)