Development and test of a multi-rotor plant protection drone for narrow spraying applications

Unmanned aerial vehicle (UAV) wind field airflow is the main factor affecting spraying width and operational effect. Under the soybean and maize compound planting mode, the width of the spray droplets of UAV aerial spraying is easily sprayed on other crops around the target crop by mistake due to the influence of the wind field. In order to solve this problem, a narrow-width spraying UAV equipped with an airflow guidance device was developed in this study, which can achieve precise spraying on target crops within a narrow operation width and reduce the impact of droplet drift on surrounding non-target crops. The wind field of the flight platform was simulated via simulation software, and the wind field distribution characteristics corresponding to three sizes of the guidance device were analyzed. It was verified that the guidance device has a segmentation effect on the wind field, and the optimal size of the guidance device was determined as 0.92 m accordingly. Meanwhile, the installation position and quantity of nozzles were determined to be set at the position with the minimum airflow disturbance. The wind speed at measuring points with different angles on four diameters at five heights under the UAV hovering state was tested through bench tests, to further verify the simulation results and appropriately adjust the nozzle position according to the measured wind speed. Outdoor flight spraying tests were carried out, and the results showed that when the 0.92 m guidance device was applied at a flight altitude of 1.00 m, the effective spray width was only 1.46 m according to the droplet deposition density on the coated paper of three test collection belts. Under the maize-soybean composite planting pattern, the field spraying test yielded results of 18.0%-30.0% deposition rate in the maize area and 0.1%-1.6% in the soybean area with maize as the operational target. A predictive effect of wind field simulation on the installation position of nozzles where droplets suffer the least wind field disturbance under aerial spraying conditions was confirmed. The UAV wind field can be effectively segmented by the airflow guidance device, and the diameter of the droplet-laden airflow column can be reduced, thus realizing narrow-width spraying.