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 26 Dossier | Hydromea Vertex AUV concept,” Schill adds. “They all have an estimate of where they are and how confident they are of that estimate, and they share that information. Then they use it together with acoustic range measurements to re-estimate and come up with a better solution. “If one has an external reference like a GPS then that obviously reduces the error. It also helps the rest of the swarm to reduce the error.” Bahr says, “This is what we are going to put into practice now. We worked with a lot of commercial acoustic comms equipment to get an idea of how it works and what it does, its performance and so on.” Two related issues that they have to address with acoustics are limited bandwidth and interference, as Bahr explains. “For my PhD I worked with big commercial AUVs, and the moment you have a modem, a DVL [Doppler Velocity Log] and an altimeter running, the vehicle interferes with its own transmissions. And where you want to put two, three or four vehicles into the water you are instantly saturating the acoustic bandwidth. “So that is why a lot of concepts have to be rethought as soon as you put even two vehicles into the water.” The basic navigation/localisation sensors are a GPS receiver and antenna system for use on the surface, and an INS based on solid-state inertial sensors for use under water, plus a pressure sensor to enable depth measurement. “We don’t have a DVL, a bottom log or anything like that because we have our acoustic ranging system, and that is used as the primary absolute reference for our position and then for relative position-keeping with the inertial system,” says Schill. However, one benefit of a general- purpose acoustic transceiver system like that developed for Vertex is that new functionality can be added in signal processing software without affecting the hardware. Bahr is confident that they will soon have developed an echo sounder capability, for example. “It has a fairly short range, but enough that if you get within ten, 20 or 30 metres of the bottom you can see the bottom and you won’t run into it,” Schill adds. Bahr notes that this is yet another benefit of designing the complete system in-house. While they could have bought and integrated an off-the-shelf acoustic modem for comms, it would have been limited to that function. The Vertex has no moving control surfaces; all manoeuvring is accomplished with the three horizontally mounted and two vertically mounted thrusters (Photo by the author) This illustration shows the positions of the Vertex’s subsystems, indicating the proportion of its volume occupied by the battery pack (Courtesy of Hydromea)