Uncrewed Systems Technology 049 - April/May 2023

96 Flying inside storage tanks The Dronut’s flaps operate on the basis of thrust vectoring principles, much like a rocket or Harrier jump jet. As air is drawn down into the duct by the fans, the flaps – which typically are pointed downwards at rest – are individually actuated to hug inwards. That redirects the airflow as it streams out of the bottom of the duct. “You would do that with a rocket’s exhaust gases, or tilt the nozzle, which causes the rocket to manoeuvre in the general direction of where the air’s being sent; our UAV changes its attitude the same way,” Eleryan says. He adds that finding servo actuators small enough – and indeed, finding everything small enough – was a challenge during development. To ensure safe manoeuvring through narrow spaces, Cleo’s software is designed to control and take inputs using multiple components, not only its forward cameras and Lidar, but LED lights for illuminating areas ahead of the UAV. “The LEDs and Lidars are key, because in these sorts of missions it’s inevitable that you’re going to end up in very dark spaces where vision doesn’t work very well,” Eleryan explains. “In the event that those aren’t enough – say the X1 flies into a 100 ft-radius tank, where the LED and Lidar ranges aren’t long enough – then we can fall back to remote control [potentially by a pilot standing by the tank] until the sensors can pick up points of reference for time-of-flight measurements within their ranges again. “Even if you have a high degree of autonomy and collision avoidance, there is still a risk of failure due to lighting conditions or lack of features, and we’ve seen instances where commercially available UAVs would respond by just veering off to one side and crashing into a wall. “And even if that were to happen to us, the severity of the impact is limited thanks to our 4 m/s maximum speed, and the propellers and electronics are guarded well enough to prevent a catastrophic failure in most instances.” In addition to flying for 12 minutes between charges, the Dronut can land and continue surveilling a target or corridor, if flight is unnecessary for a given objective. The battery contains enough energy for up to 60 minutes of operation without flying, such is the sensor and onboard computing power. Primary perception comes from the 4K vision camera, with the Lidars acting as a secondary perception tool to verify or substitute the camera data as necessary, as well as an inspection tool. The Lidar’s point clouds are outputted for the end-user to download and analyse after themission. The Lidar itself is a photonic mixer device sensor from PMD Technologies. Its system integrates a sensor element as well as its electronics for signal processing on a single silicon chip, enabling highly accurate measurements in an industrial-grade housing. Also, its small laser light spot makes it suited for detecting small parts and details, not only for high-resolution mapping but 3D modelling and inspections as well. “We get a 100 x 100o FoV with each Lidar, and an effective range of up to 6-7 m,” Eleryan says. “That’s ideal for the kinds of confined spaces we want to work in.” And while Lidars tend to be the most power-hungry system on a UAV, he adds, “They’re actually very low SWaP, which again is something that’s inherent in the PMD design, and helps us get the most out of our batteries.” Asmentioned, a 4K camera, a global shutter camera, and the PMD Lidar are installed at the front, although in the near future Cleo plans to upgrade the X1 with several additional 4K cameras and four more Lidars (alongwith an improved radio), distributed about the airframe for full awareness of its surroundings in all axes. “We already have a fair amount of overlap with our sensors’ FoVs in the front, and with the new design there’ll be some overlap at the rear and sides, though not as much, because naturally the idea is that users will still primarily fly the UAV forwards,” Eleryan says. Real-time decision-making regarding April/May 2023 | Uncrewed Systems Technology A photonic mixer device Lidar enables highly accurate point clouds with minimal SWaP requirements