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94 In operation | Global Unmanned Spray System “That whole combination was very challenging to get dialled in,” Thompson says. One issue that arose was training the software to ignore low-hanging nuts, specifically almonds. Faced with the returns from heavily laden branches, it initially interpreted them as obstacles and stopped the vehicle. Now the operator tells the system what type of trees it will be spraying, and the GUSS will push under the branches without harming them. Communication is via cellular radio, eliminating the need for any infrastructure in the orchard, although growers with coverage are installing their own towers. One operator/supervisor can manage up to eight GUSS vehicles using an interface running on a laptop in the cab of a pick-up truck. At the start of the working day, the checks GUSS needs are very much like those that have to be done on any tractor and spray rig. They include making sure the diesel tank is full, applying a grease gun to the lubrication points, checking the oil and coolant, making sure the engine air filter is clean and filling the spray tank. Wiping the Lidar with a microfibre cloth is one significant difference, and giving the vehicles their orders is another. Three-step set-up Setting up the GUSS for a spraying operation is a three-step process, Thompson explains. “When you spray an orchard for the first time, you first have to build a map of it. We download a Google Earth image of the orchard [or the whole farm], mark the corners of it and put in the tree row spacing. Hitting Enter builds a grid across the whole orchard with a driving row every 20 ft, or whatever spacing is programmed in.” At that point, he says, the operator looks for any obstacles and marks them with caution points. He then adds no- drive zones to keep the GUSS away from an irrigation pump or some other piece of equipment, and no-spray zones through which the vehicle will drive but turn the spray valves off. “That can be handy if you have centre avenues that you’re going to drive across while spraying.” With the map built, it is then checked for ‘ground truth’, Thompson says. “We’ll go out there with a pick-up and check certain spots, because the satellite images are never perfectly accurate, so we might have to move our lines a little. Then we save that map, and we’ve got it for the life of the orchard.” Configuring the sprayers The next step is to configure the vehicles, telling them the speed at which they are to drive, the engine rpm to use, the pump pressure and flow rate of the spray system. “The good thing about using a computer for this is that if you tell it to drive at 2.2 mph it will do that all day long,” he says. “The spray materials are expensive, so you want to make sure you’re putting them on the trees in the proper way.” Another key parameter to set up is the number of rows to spray before stopping to wait for a refill from one of the ‘nurse’ trucks. Driven by one person, each one supplies up to four spray vehicles, filling them from a large tank in which the chemicals are mixed with water and kept in solution by an agitation system. February/March 2020 | Unmanned Systems Technology The diesel-powered GUSS with its obstacle avoidance/ navigation Lidar, forward-facing camera, chemical tank and ring of fan-assisted spray nozzles at the rear The GNSS antenna is given the best view of the sky available, but fruit-laden trees can interrupt the signal, so enabling the GUSS to navigate independently of satellites was the greatest challenge in its development