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80 over the VHF band, as all commercial boats in Amsterdam are required to do. That’s useful for individual and group USV path-planning, as they can avoid very busy commercial canal sections well in advance. “Also, if these boats are going to be travelling the canals, there will need to be an overarching traffic management system, controlled by the port authorities or the municipality, or any other overseeing body for ship movements in certain areas. That is possible by using wi-fi links, GNSS tracking, sensors and so on.” Autonomous docking and latching When they arrive at their pick-up destination, an effective method for docking and station-keeping multiple boats at a time will be needed for collecting the waste bags and bins. The Roboats will therefore use a mechanical latching mechanism to connect to each other; one of them can also dock at the quayside in the same way. This will eliminate the need to have people on the boats to lash them together. The current prototype for the mechanism uses a spherical ball-and- socket joint that allows rotation and free movement in two planes. The mechanism works by fitting a tag that resembles a simplified QR code to each docking station, or connecting boat, with a camera installed that recognises the tag (similar to a beacon) and thus calculates the USV’s exact position and orientation relative to the tag. Using that information feed from the camera, the Roboat steers itself towards the tag. Keeping the camera and tag perfectly aligned allows the Roboat to connect and latch on precisely. The latching system also enables Roboats to dynamically create floating infrastructures such as bridges, market floors or concert stages, while minimising water disturbances that could upset the balance of people or objects standing on them. After assembling into larger platforms, multiple vessels can coordinate themselves as needed for a multi-vessel structure, using the communication and sensing systems across all the USVs. A leader boat would take over the control of all the Roboats’ thrusters, enabling multiple Roboats to perform complex manoeuvres in an orchestrated manner, similar to a swarm of UAVs. “We’ve developed several iterations of the latching/docking mechanism to optimise for grip angles and forces, which we’ll be testing further later this year,” Deinema says. “We’ve also experimented with electromagnetic connections, other mechanical connections and similar suction-based couplings to those used to refuel aircraft in mid-air.” The docking mechanism will naturally also be key for securing the Roboat at the drop-off point for its waste cargo. The team is currently researching the best way to distribute the waste – once collected – to its endpoint. For example, there is a waste incinerator outside Amsterdam’s city limits, so the Roboat could provide an energy-efficient means of transporting refuse there. “Alternatively, the Roboats could transport their waste to a central location and a larger boat, or perhaps a bigger and more powerful future variant of it could tow it to the incinerator while the rest continue working around the centre,” Deinema says. “As you may have guessed, the thrusters are quite a bit stronger than what is necessary for the 6 kph canal speed limit, but the additional power and torque could be used for a towing operation, where one or two Roboats lead a string of them whose power has been switched off to save battery electricity.” Pedestrians could also benefit from the researchers’ abilities to link multiple Roboats together into a bridge, to offer shorter walking routes during events (as reported in UST 29, Dec 2019/Jan 2020). Water trains for commuters or large platforms for farmers’ markets are also touted as potential future uses. April/May 2020 | Unmanned Systems Technology Roboats can latch on to each other or a quay wall using a mechanism consisting of a spherical ball-and-socket joint, which allows some rotation and free movement (pictured here on the quarter-scale prototype)