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93 of spray nozzles and a fan at the back for atomising and dispersing the spray. The engine is a 173 hp diesel, which powers hydraulic drives and steering for all four wheels as well as the dispersal fan, which absorbs most of the engine’s power. Automation challenges With the platform essentially complete, the process of automating it took about three years, but it faced considerable scepticism from people who pointed to the problem of poor GPS reception under trees, Thompson explains. He adds that the biggest development challenge was figuring out how to operate without a GPS signal, for which a big part of the solution is a front-mounted Velodyne Lidar – with a fan to keep dust off the lens. This is used for obstacle detection and to locate the trunks of the trees on either side of the GUSS’s line of advance, using its control system software to keep it centred in the row. The system also has wheel rotation counters to measure the distance travelled and steering angle sensors, both of whose output it integrates with the Lidar and, when available, GPS signals. The software also makes judgements about the reliability of each source of information on the fly. Global Unmanned Spray System | In operation their labour Unmanned Systems Technology | February/March 2020 Dave drew on the shop floor what he thought the world’s first unmanned orchard sprayer should look like, and some fabricators started welding it up The GUSS is now in operation spraying orchards in various US states, navigating with a mix of GNSS, odometry and Lidar according to pre-loaded mission (Photos courtesy of GUSS Automation)