Unmanned Systems Technology 021 | Robot Aviation FX450 l Imaging Sensors focus l UAVs Insight l Liquid-Piston X-Mini l Riptide l Eurosatory 2018 show report l Zipline l Electric Motors focus l ASTS show report

65 UUV. For example, the pEvalLoiter module evaluates the efficiency of a vehicle conducting a loiter mission. It can be used in conjunction with the uFldCollisionDetect module to gauge how well a vehicle is balancing collision avoidance safety with mission efficiency. Other BeagleBone Black cards are used to manage power, propulsion and control, although these could be a Raspberry Pi 3 board or an Nvidia Jetson processor card instead, depending on the system or sensor requirements. “We can easily put a backseat processor on the vehicle, have it generate a behavioural response from the sensors and feed that back into the MOOS,” says Smith. “The choice of processor depends on the horsepower required for automatic target recognition and sonar, for example.” Mission planning is handled by OpenCPM software and a graphical interface running on a laptop. The waypoints for a mission are generated in the application, and the team developed interface software (a translator) that converts the OpenCPM data into the format for MOOS. The UUV can then be operated from an iPhone or iPad in the field without the laptop. The Riptide team is currently integrating a sonar sensor into its whole range of UUVs using another BeagleBone Black card. “This provides an affordable, flexible tool,” says Smith. “The controller is the same board for the tail controller for the larger servos. “From a payload perspective we are starting to get into a larger payload controller that takes more power. That’s really attractive for developing behaviours on the little vehicle and transferring the data to a larger one with a larger sensor, where you can trade off the energy requirements and payload. It’s a balance of what you want the vehicle to do.” On the power side, the efficiency of the system design provides eight to ten times the endurance of other A-size UUVs, which typically operate for six to eight hours without a payload. The Riptide design operates for 40 hours without a payload on alkaline batteries. The alkaline batteries are a requirement for the US Navy: there are safety restrictions on transporting lithium batteries around the world, as they can catch fire if damaged. With a lithium power pack, the system has an operating life of 80 hours. That comes from reducing the power consumption of the overall system to 3.8 W, rather than the 35 W of other UUVs. The first Riptide prototype used 18.5-20 W, while the first system delivered to a customer used 9 W and the second generation now uses the 3.8 W. The design has also focused on hydrodynamic efficiency. “This is two to three times better than other designs,” says Smith. “We do a lot of work on the shape and the propeller. For example, we integrate the electronics into the fin so that we are not adding size. “We have also taken a lot of the wiring out of the vehicle with stackable boards and by using the latest components. We are not wedded to the BeagleBone Black; we are looking at the Raspberry Pi 3 and maybe the Pi 4.” Cost reduction The key to reducing cost is a lot of smart engineering, he says. “We had a very minimalist approach to the vehicles Riptide Autonomous Solutions | Digest We do a lot of work on the shape and the propeller. We integrate the electronics into the fin so as not to add size Unmanned Systems Technology | August/September 2018 The integrated dorsal fin provides comms, a recovery strobe and GPS. The tail also houses an emergency drop weight and provides external ballast and trim