Skygauge UAV ultrasonic inspections | In operation results are beamed down into a little map of the inspection plan, so the inspector can view it.” The ultrasonic gauge system for measuring wall thickness has been developed and supplied by Evident Corporation, formerly part of Olympus Corporation until the latter split off its Scientific Solutions Division into the former, now an independent company. “They’re the existing world leader in this kind of technology, and we’ve been working closely with them to integrate their conventional sensor into our UAV and tailor it to be more of a robotics solution than a manual, handheld one,” Korol explains. “They’ve helped us a lot with integrating the unit, providing a lot of open detail on its workings, as well as just supplying us with units for R&D and then product purposes.” Windspeeds are computed based on GNSS position, with a dual-antenna and receiver GNSS and inertial navigation system (INS) onboard and embedded with Skygauge’s algorithms for wind prediction. The angles taken by the servo motors to maintain contact are also useful data inputs for understanding wind directions and speeds in those algorithms. A single-point, laser rangefinder system is installed on the UAV, which serves as the primary sensor for distance between the UAV and the wall. Based on that data feed, the autopilot slows down the flight speed as the wall gets closer and closer, from 20 cm/s at the initial approach to 3 cm/s at the point of impact. A 1080p camera with 60 fps is also used to enable situational awareness; significant algorithmic work for the camera has enabled it to detect obstacles in the dark and provide useful, high-resolution imagery of the structures being inspected. “All of that data is critical for how we’re trying to digitise these inspections. This kind of work is traditionally very pen-and-paper. Literally, they would write the results and commentary from inspections on to pieces of paper, which would frequently then go missing, but we generate video and photo data, ultrasonic waveform models showing the full thickness, GNSS and altitude data, and so on,” Korol adds. Contact is detected via a force torque sensor on the end of the arm, which measures the quality, force and torque being exerted between the wall and the UAV. As well as preventing excess force being imparted on the UAV, this data feed also helps the UAV to stay level via the flight-control system maintaining a target pressure level for the aircraft to keep to. “We like to push with about 2 kg of force to conduct the inspection correctly. You do have to press an ultrasonic tool a fair bit for it to work, and that’s another benefit of our articulating thruster design: we can push forwards quite significantly with our rotors,” Korol notes. In-flight mechanics Some past designs we have seen for solutions aimed at using UAVs for physical work (particularly on highrise structures), such as painting or coating applications, would feature a pusher propeller (powered by an electric motor) extending from the back of the multirotor. This would ideally enable forward motion in a linear manner, without requiring the UAV to pitch down, hence enabling a level mode of contact, as well as sustained pressure against a wall via the thrust from that pusher prop. “We have considered those kinds of designs, but they didn’t really appeal to us,” Korol says. “We’ve found that solutions like that, which dance around the core issue of drones needing to tilt around in order to move, ultimately mean that once a bit of wind comes in while you’re conducting some kind of physical work, the UAV and autopilot naturally resist the push and pull of that wind. They have no choice but to tilt around, to lose accuracy, to lose stability and contact; it’s just not going to work. “We’ve seen dozens of projects like that, which try to engineer around that problem and maybe see some success in lab situations, but practically speaking, the real world has too much wind and too much precision force requirements. “Frankly, until you dive deep into the challenge and do a total rewrite of how your flight-control architecture works, to isolate the motors and allow them to act separately from the airframe, you’re just going to keep bumping into the same problem.” 99 Uncrewed Systems Technology | February/March 2024 Once at the GNSS and altitude of an inspection point, the UAV locks in to station-keep at about 50 cm away before approaching slowly
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