Unmanned Systems Technology 036

61 Bouabdallah could see that to maximise the flight time, he would need to find a way to maximise the propeller sizes. To maximise the diameter and chord of the prop blades, while fitting them inside a cage, he would need to fly the UAV using two centrally mounted props in a coaxial bi-copter configuration. And to ensure stable, controlled flight with such an unusual rotor-wing design, he would need an entirely new kind of control system to take care of the mechanical and electronic aspects of propulsion and steering. With these goals in mind, he worked on a number of technological solutions, forming Flybotix in 2019 to develop and manufacture a UAV incorporating them. That UAV is the Flybotix ASIO, which was unveiled last October as a coaxial bi-copter housed in a 395 mm-wide and 295 mm-tall cage. Its total weight is 1 kg, with the cage weighing just under 100 g. The craft carries an EO/IR gimbal, along with an array of SWaP-optimised sensors for stable navigation in limited- GNSS and space-constricted conditions. It also embeds numerous algorithms for performing user-adjustable manoeuvres based on data from those sensors. Caged airframe Various caged airframe UAVs have been developed around the world, and Bouabdallah himself led a team between 2006 to 2009 to produce the muFly caged UAV at ETH Zurich. Although the ASIO’s cage appears structurally and geometrically simple compared with some of those other UAVs, Bouabdallah says it went through seven iterations before the final version was arrived at. “We have two patents on the cage, such is its importance, because a lot of different properties and constraints have to be managed,” he explains. “For one thing it has to be lightweight, because every gram you add cuts flight time by a few seconds. “Even so, it has to be resilient to collisions to prevent damage to the UAV, and cutting weight can hamper that, yet if it’s too rigid it’ll bounce from impacts and disturb the flight path. It has to absorb impacts with just a bit of inward ripple or ‘crumple’, independent from the centre of balance.” The design of the cage also had to be kept simple so that customers could replace it easily on-site. To that end, two hooks are unclasped at ASIO’s front and rear sensor brackets to detach a damaged cage; it can then be folded and stowed, and a new one installed, all within a few minutes. The cage consists of 10 longitudinal polymer composite spars that serve to withstand and absorb the initial force of impacts. They are joined at their top and bottom poles by a pair of specially designed fasteners. Tschudi adds, “It’s hard to gauge the size of impacts that the cage can handle: there’s a huge variability in speeds, directions and the hardnesses of objects an ASIO might accidentally bump into. That said, we’ve test- dropped it from 1.5 m, and both the craft and cage were undamaged.” The powertrain The ASIO’s movement from one area to another is controlled by a patented system similar to the kinds of swashplates traditionally used for orienting helicopters’ propeller blades for moving forwards, sideways and backwards. Flybotix ASIO | Digest We have two patents on the cage, such is its importance – a lot of different properties and constraints have to be managed Unmanned Systems Technology | February/March 2021 The ASIO’s cage is constructed from 10 longitudinal composite spars to withstand and spread the force of impacts