Unmanned Systems Technology 042 | Mayflower Autonomous Ship | Embedded Computing | ElevonX Sierra VTOL | UUVs insight | Flygas Engineering GAS418S | Ocean Business 2021 report | Electric motors | Priva Kompano

59 ElevonX Sierra VTOL | Digest electrical noise. A heated pitot tube can also be offered for customers working in wet weather to prevent clogging of the airspeed sensor, although ElevonX has found that customers rarely seek to perform mapping or other missions in such conditions. Although the Sierra VTOL does not typically broadcast its position, the Cube Orange contains an ADS-B receiver, making sense & avoid possible. Langus notes that the University of Tubingen has successfully integrated a Flarm transceiver from Aerobits into its UAV, so certified transmission and reception of air traffic data is clearly achievable upon request. Flight control network The Sierra VTOL operates using four servo actuators, one in each wing’s aileron and two in the tail elevons. Hitec servos are installed, based partially on word-of-mouth recommendations from other Hitec customers but also on the actuator company’s available supply capacity, as well as the portfolio of products it offers. “Their range of servos, in terms of different technical specifications across different units, is quite broad, which means we were able to select ones with parameters that were best for our use case,” Langus says. “We are using some of their higher voltage, 7.4 V DC systems. That is a bit higher than usual for our weight class but it allows us to use a lower current than other UAVs, which in turn enables us to run our servos with higher power and lower losses.” He notes also that the Hitec servos are IP67-rated, enabling them to be submerged for up to 30 minutes – a test ElevonX has run itself using an in-house test aquarium – and still work perfectly afterwards. “Even if that isn’t necessary for how our VTOL will be used, it’s still really reassuring to know the servo actuators are that reliable,” Langus adds. Currently, a PWM link delivers commands between the autopilot and the servos’ ESCs, but for all onboard sensors UAV-CAN is used. The company is also moving towards servos that are capable of communicating in this protocol, and will work as drop-in replacements for the current systems (specifically, systems from Hitec that now come with UAV-CAN). “UAV-CAN is more expensive but much more robust than PWM, and it allows you to get back a host of operating data from your servos and other components for running diagnostics,” Langus says. “We’re testing the new servos, but we want to be absolutely sure they perform perfectly before we put them into our production lines; we’ll know whether we want to go in that direction after a couple of months or so.” For carrying sensor and control signals securely, ElevonX trialled products from several connector suppliers but eventually selected push-pull circular plugs from Hirose Electric, having found them very useable and practical in how they handled and assembled. The resilience of its supply chains also meant it could sign and guarantee the bulk orders of connectors ElevonX needed, with far shorter lead times than the 6-8 weeks offered by other suppliers. “They’re also IP67-rated, and the number of mating cycles they have is in the thousands,” Langus says. “We change connectors regularly as part of our service intervals, but having ones with long lives is really important so as not to not disrupt clients’ missions too much with maintenance tasks.” VTOL transitions The transitions between vertical ascent (or descent, or hover) and forward flight is handled through the Cube Orange’s Ardupilot software, using an algorithm developed for VTOL transitioning via four fixed electric motors on a UAV’s airframe, and published and obtained through the open-source network. “This is quite a well-tested algorithm,” Langus comments. “A lot of developers have used and improved it over time, long before we installed the latest stable version onto the Sierra VTOL, and we’ll often test the newest versions of it on smaller-scale versions of the UAV. The flight software incorporates two flight modes. The first is in essence a quadcopter architecture, and this is the active mode when the Sierra VTOL starts up, on the ground. That mode targets, maintains and prioritises the craft’s wing level and angle parallel with the ground, based primarily on information from the IMUs and magnetometer, until the aircraft Unmanned Systems Technology | February/March 2022 The Sierra uses four servo actuators, one in each of the two ailerons, and one in each tail elevon