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19 small, off-the-shelf DJI Phantom UAVs with chemical-spraying equipment to kill vegetation growing high up on buildings and other structures, but the project was halted. “It wasn’t really pursued because Mitie saw itself as a services provider as opposed to a product manufacturer or developer. It was a good idea, but it was never taken anywhere.” At that point, the company sold that part of its business to pest control company Rentokil. The desire to pursue their ideas for UAV services and develop their own products is the primary reason that Young, along with operations director Clayton Earney and communications director Toby Townrow, left to form Drone Evolution in 2018. Keep it simple Asked about his personal philosophy of engineering, he says the ‘keep it simple’ adage sums it up. In that respect, the engineer he most admires, almost to the point of regarding him as a mentor – if a distant one – is renowned firearms designer Mikhail Kalashnikov. “Everything he produced in the Soviet Union was very simple, with very wide tolerances, but they work,” he says. “The tighter the tolerances, the more environmental problems you get,” he says. The smaller clearances that tight tolerances enable often result in mechanisms that are more sensitive to contaminants such as dust. Applying this philosophy to the company’s products involves building concept demonstrators in-house using basic tooling and then taking them to a development house with more sophisticated machinery capable of achieving much tighter tolerances. “They take our basic designs and come back to us with their take on it, and we end up somewhere in the middle with something that really just works, and works every time,” he says. Young applied these principles to the SkyWire universal tether system, which is designed to power any electric VTOL UAV, enabling it to hover for long periods. It is intended primarily for small UAVs. “It is fairly simple to tether a large UAV, but more difficult with a small one because of the lack of payload capacity,” he explains. “So we set out to develop a very small aerial power supply, a very lightweight tether and a very mobile ground power system.” He adds that SkyWire’s development is almost complete and the system is now being marketed. The company also offers a package including the Dragon Tethered Drone UAV. Engineering challenges The main engineering challenges, he says, centred on weight, power and redundancy. The effort went into “converting the power from the ground up the tether, overcoming any losses and coming up with a very stable way of supplying the voltage and current to the airborne UAV.” For a given amount of power to be transmitted, he explains, increasing the voltage reduces the current and allows the use of a thinner, lighter cable. “Generally speaking, tethers run at very high voltage – either AC or DC – and carry a lower current, although some use lower voltage and higher currents. We sort of settled midway,” he says. “To do what we needed to do we went for 250-300 V, with a couple of amps going up the tether.” John Young | In conversation Unmanned Systems Technology | December/January 2020 As well as 12 V civilian vehicles like this pick-up, the Dragon Tethered Drone system can also work on 48 V military vehicle power, allowing almost any electric VTOL UAV to hover for several hours The SkyWire tether system runs at voltages between 250 and 300 V with around 2 A of current, enabling a slim cable and lightweight power conversion electronics aboard the UAV