Unmanned Systems Technology 028 | ecoSUB Robotics AUVs I ECUs focus I Space vehicles insight I AMZ Driverless gotthard I InterDrone 2019 report I ATI WAM 167-BB I Video systems focus I Aerdron HL4 Herculift

94 Digest | Aerdron HL4 Herculift avionics company Drotek to fine-tune the gains of the autopilot’s PID controller. That got us 90% of the way there in terms of fine-tuning the autopilot before the first flight,” Marcos Fabian adds. All the structural attachment components are CNC-machined from 6061-T6 aluminium alloy, for strength and durability. In order to finish the project in the limited time span, the chassis was made from aerospace-grade prepreg carbon composite sheets and tubes, built in sub-assemblies, and a jig used for final assembly. Once on the jig, the parts were riveted together and bonded with Hysol structural adhesive. Designing the HL4 relied particularly on the use of 3D CAD, with key objectives being to get the hull ‘packaging’ as tight as possible around the batteries and other internal electronics, to minimise chassis size and weight. The CAD models for the structural components were taken to local CNC and water-cutter shops. Extruded carbon fibre preforms were used for the composite beams in order to fit the project budget – future HL4s will use a composite moulded sub-frame to optimise weight and minimise assembly time. Aerdron anticipates this will reduce the aircraft’s empty structural weight by as much as 15%. The motor mount flange’s thickness was thinned out as much as possible to save weight, and that part was designed as dual load path structure. This means that if a crack is propagated in any critical area it will not develop into a structural failure: the cracked motor mount will still be able to take the full motor thrust load and assure a safe landing. For the first complete HL4 prototype, the weight was within 7% of what the engineering team had estimated in its original hand calculations. The company also designed the HL4’s transportation case, which in addition to the aircraft holds two pairs of battery modules; it is also ruggedised. Lifting power The HL4 uses two Tattu 22000 battery packs connected in series. Each pack consists of four cells in series to produce a total of 14.8 V and 22,000 mAh (from which the name is derived), and weighs about 1.7 kg. The batteries mount onto a carbon fibre tray and are fastened directly into the structure. Future versions of the HL4 will use a ‘quick-release’ system though, to enable tool-less battery swapping that would take less than a minute. A battery management system from Drotek was selected for its power redundancy features as well as algorithms and filters for health monitoring, surge protection and other critical electrical functions. Lift is provided by four P80 electric motors from T-Motor, each of which provides up to 17 kgf of thrust. They contain 36 permanent magnets and 42 manually wound stator poles. It might seem curious that the craft uses four motors rather than eight, but early in the development process October/November 2019 | Unmanned Systems Technology The HL4 uses two 22,000 mAh batteries fastened into dedicated compartments on either side of the airframe body, although future versions will have a tool-less quick-release system The folding propellers originally used were found to vibrate during take-off, so they were swapped out for fixed versions