Unmanned Systems Technology 018 | CES show report | ASV Global C-Cat 3 USV | Test centres | UUVs insight | Limbach L 275 EF | Lidar systems | Heliceo DroneBox | Composites

34 Dossier | ASV Global C-Cat 3 USV on an Intel x86 processor that runs the vessel’s control software. All the intelligence is on the vessel itself, but the planning can be done remotely at the user interface and transmitted to the vessel. Customers typically plan survey work using their own software and then download the mission and run it from the ASView interface. The operator can choose between direct control with joysticks for close- in manoeuvres when they can see the vessel, or use the onboard camera to move in close to something. The above- mentioned oil pier inspection job might be an example where manual control would be used, the operator relying on the camera feed and the other sensors to thread it around the obstacles. Manual control can also be used for collision avoidance, but there are other options for this, such as pre- planned actions. “You can put it into a heading-hold mode or on to a track-hold mode so that it will go down a line in a direction you want without crabbing into the tide, and then resume the mission,” Daltry says. The C-Cat 3 also has a very basic automatic collision avoidance system thanks to its Automatic Identification System (AIS) receiver, which allows it to work out whether it might be coming into conflict with any other AIS-equipped vessels. If necessary, it will stop to let the other vessel pass before continuing its mission. Daltry emphasises however that this does not comply with maritime COLREG collision avoidance rules, although the company is building on its autonomous navigation capabilities in its larger vessels, which feature other sensors such as Lidar and vision systems. Communications The standard comms system is 802.11 wi-fi using an off-the-shelf modem optimised for maritime use. Wi-fi was chosen because it is a cost-effective way of providing useful bandwidth over relatively short ranges. Daltry cautions that care has to be taken here to avoid interference, although the modem has the ability to scan the available channels and choose the best one. As an option, customers can specify digital radios with coded orthogonal frequency division multiplexing (COFDM) capabilities to deal with multi-path reflections off the water surface or nearby structures. The pier inspection job would again be an example of where COFDM would come into its own, given its ability to assemble reflected radio signals into a strong comms signal. These radios, Daltry says, provide a major step up in range at the cost of some bandwidth, although they do maintain their bandwidth out to the maximum range. Another option is to integrate an Iridium satcom link, as the company routinely does on its larger USVs to serve as a back-up transponder. It also provides the ability to control the vessel by sending manoeuvre commands to the autopilot in the form of short-burst data messages. Safe methods of dealing with a loss of comms is a crucial part of any unmanned systems company’s safety case. In the C-Cat 3’s case, the options are to stop, to go into station-keeping mode by circling a chosen waypoint, to run a back-up mission plan or pre-program it to head for a known safe space. ASV is also considering a mode that takes it back to where it last had a signal. Navigation In terms of navigation accuracy, ASV works to a cross-check error of 2 m or less, although the autopilot often easily beats that, Daltry says. Customers work to a much greater accuracy though, and typically fit survey- grade GNSS receivers with real-time kinematic (RTK) correction capabilities that bring the error down to a centimetre, or 5-10 cm if they are using a satellite- augmented system. While the vessel’s navigation system can take a feed from such a receiver, ASV’s engineers have integrated a GNSS receiver into an embedded processor aboard the vessel and in the land-side control station to implement a simple RTK solution. “So long as we can get a fix on the land, it can work as an RTK base February/March 2018 | Unmanned Systems Technology The mission control station in ASV’s Portsmouth HQ can run multiple vehicles anywhere in the world via the cloud (Author’s image)