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

96 “After installing those the craft flew beautifully, and all those vibration issues were gone. We could certainly use similar folding propellers in the future with just a few design tweaks, but because of the short project time limits, the best option for the prototype was to replace them.” Autopilot The autopilot is a Pixhawk 3 Pro from Drotek. Based on the open-source PX4 autopilot software architecture, the system met the client’s requirements since it planned to use the sensor data from the autopilot with its payload, while its software’s open-source nature made accessing and extracting that data a simple process. Drotek also provided flight test consulting in order to fine-tune the autopilot gains to match the stability and control characteristics of the HL4 with different payload weights. It provided the data link that operates on the 433 MHz band as well, with a range capable of exceeding 5 km. “We went through a huge amount of engineering calculations and parameters,” Marcos Fabian says. “We moved the GNSS position around to mitigate magnetic EMI/EMF interference from the motors, then we made some changes to the autopilot suspension system to clean up some of the vibration and interference issues. “Being open source, the autopilot architecture made it much easier to alter and view the parameters and behaviours to adaptively fit our various inertia profiles for different payload weights. All the third-party open-source ground station software and other modelling programs were compatible with it too. “The Drotek autopilot and their other onboard electronics – two GNSS modules, a power management system and data comms modules – also performed as needed.” Two GNSS receivers are installed for redundancy (along with voting software for selecting the correct GNSS signal if two different sets of navigation data are being received), and a downward-facing laser altimeter with a 120 m range is also integrated to provide accurate and stable take-offs, landings and to stay on station for precise hovering. “The laser altimeter gives a huge step in precision and redundancy over just relying on GNSS coordinates during hover, which was an important requirement for the customer’s mission profile,” Marcos Fabian notes. Payload integration As per SENER’s request, a ‘universal’ mounting plate is fastened atop the middle of the craft by eight M3 bolts. A carbon fibre or aluminium payload plate sits on the carbon fibre chassis, and allows payloads to be uninstalled and replaced in an easy plug-and-play form. Its size – 320 x 300 mm – also serves to encompass a zone within which the centre-of-mass envelope can vary without significantly altering the UAV’s controllability. “SENER have tons of different products and applications they want to test – not only comms equipment – so October/November 2019 | Unmanned Systems Technology Battery-powered quadrotor aircraft Size: 166 x 166 cm MTOW: 25 kg Payload capacity: 11.9 kg Payload area: 320 x 300 mm Battery capacity: 44,000 mAh Maximum endurance (no payload): 30 minutes Endurance at payload capacity: 13 minutes Data link range: 1600 m Some key suppliers Composites: GRM Composite Systems Composites: Easy Composites Electric motors: T-Motor Propellers: T-Motor Batteries: Tattu BMS: Drotek GNSS: Drotek Autopilot: Drotek Data link: Drotek CNC machining: Controlmad Specifications The payload plate effectively demarcates an area in which the centre of mass of a payload (pixellated by request) can vary without changing the HL4’s centre of gravity