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6 Mission-critical info for UST professionals Platform one UAVOS has developed a large UAV that has a distributed autopilot system (writes Nick Flaherty). The Saker-1B MALE UAV was developed with the King Abdulaziz City for Science and Technology, in Saudi Arabia, and has a take-off weight of 1200 kg. “For this project we supplied all the electronics, the integration of the autopilot, servo drives and also tuned them for the autopilot,” said Aliaksei Stratsilatau, CEO of UAVOS. UAVOS first developed the distributed autopilot (AP) system for a high-altitude pseudo-satellite with flexible wings. It uses a series of APs connected together to control the whole aircraft, similar to formation flying. The distributed AP was adapted to add layers of redundancy. The first is redundancy on servos, then on the sensors. There are multiple three-axis MEMS, laser gyroscopes and IMUs across the platform. The third layer is in the networks. There are three CAN systems acting in parallel, each with its own IMU, GPS, interface controller and power distribution controller. The AP for the Saker-1B is built using a distributed computing architecture. Each network provides controls for the servo drives independently, constantly diagnosing component health. When a network receives signals for the servo drives, all three networks vote on the correct command, selected by two out of three voting. Each control surface has two servo drives, and each wing has three ailerons – inner and outer – that act as flaps and ailerons at the same time. So, if one servo fails, only one-third of the control surfaces fail. “We have tested this, and the aircraft can fly with two failures on a wing,” said Stratsilatau. The low-level functions of the APs are distributed throughout each network. For example, estimating the position of the aircraft uses the AHRS, GPS and navigation controller. These use a small STM32 F4 microcontroller from STMicroelectronics that also runs some of the autopilot functions. That means the AP is not a single heavy box, as it is based on the small microcontrollers. Instead it is implemented in five units that weigh a total of 1 kg, including IP67 cases and military-grade connectors. This creates challenges in the safety verification, as there is no way to describe or confirm the safety of the system based on standard procedures. However, UAVOS has experience of such qualification processes from several other projects. “We are now building the third generation, with improved specifications such as higher take-off weight and longer endurance, which is up to our Saudi partners,” Stratsilatau said. “The first flight test is scheduled in the next few months. The only things that remain are the approvals and test flight.” Airborne vehicles Flying on autopilots April/May 2020 | Unmanned Systems Technology The Saker-1B has three autopilots distributed across three CAN networks to provide redundancy