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7 Platform one DJI has applied for a patent in Japan for a variable geometry multi-copter that can reconfigure itself in flight to give its sensor system a view beneath the vehicle that is completely unobstructed by the airframe (writes Peter Donaldson). In application number JP2018150048A, Chinese inventors Tao One, Tao Geo, Hao Du and Minshi Wan propose a vehicle with a central body carrying the sensor and comms package. The design includes at least two pivoting arms connected to the central body at one Researchers in Singapore have developed an autonomous quadcopter that can run entirely on solar cells, making it independent of a battery pack (writes Nick Flaherty). There have been many solar-powered fixed-wing aircraft, such as the Aquila and the Zephyr, where solar cells on the wings can provide power for both the propulsion and battery charging, but generating enough power for rotors to provide lift has been a major challenge. The team at the National University of Singapore developed a UAV with four rotors powered entirely by 148 solar cells with a total surface area of 4 sq m. The system weighs only 2.5 kg as it does not use a battery, and has reached a height of 10 m in test flights. The solar cells had to be individually characterised to ensure they all produced a reliable current in the same voltage range. “Our aircraft is extremely lightweight for its size, and it can fly for as long as there is sunlight, even for hours,” said Associate Professor Aaron Danner from the Department of Electrical and end, and a crosspiece at the other, each supporting two motors, their propellers and a landing leg. For take-off, the landing legs are on the ground while the central body is held off the ground above them. In flight, the mechanism is lowered and inverts the central body so that it hangs underneath the propellers. Each arm consists of a primary and a secondary shaft, and the arm is moved by an actuator assembly that can be connected to either shaft in different variants. Single or multiple drive units Computer Engineering at the Faculty of Engineering. “Unlike conventional quadcopter drones, our aircraft does not rely on onboard batteries, so it is not limited by flight time. Its ability to land on any flat surface and fly out of the ground effect in a controlled way also makes it suitable for practical implementation.” The quadcopter can be controlled remotely or programmed to fly autonomously using a GPS system incorporated into the aircraft. and actuation mechanisms can be used, depending on whether the aim is to make the arms independently moveable. The inventors say the actuation mechanism itself could include combinations of gears, shafts, pulleys, screws, nuts, spindle, belt, cable, wheels, axles and so on, powered by electric motors, and may even include hydraulic linear actuators. The mechanism is located in the centre body along with the payload, autopilot and the radio links for flight control and payload control. “We encountered many engineering challenges when building the UAV,” said project supervisor Brian Shohei Teo. “These included finding an optimal number of solar cells that are efficient and light enough to power the propulsion system, which in turn has to be light and at the same time able to produce sufficient thrust to lift the aircraft. “Other issues included tuning and calibrating the flight controls to enhance flight stability, as well as designing a frame that is lightweight yet sufficiently rigid.” Clear-view sensor idea Batteries not included Airborne vehicles Airborne vehicles Unmanned Systems Technology | December/January 2019 The quadcopter can run purely and ‘for hours’ on solar cells