Design and Test of a UAV-Based Oscillating-Tube Broadcasting Device

A multi-rotor UAV-based oscillating-tube broadcasting device incorporating replaceable material-specific screw metering units was developed for low-rate seed and granular-fertilizer application. The key structural parameters of the oscillating tube were screened through theoretical analysis and single-factor experiments using pre-germinated conventional Huanghuazhan rice. An L16(43) orthogonal experiment was then conducted solely for exploratory screening of the main effects of flight height, forward speed, and broadcasting material on the single-pass broadcasting-uniformity coefficient of variation (CVb) and effective spreading width (We). Forward speed significantly affected CVb, whereas all three factors significantly affected We, with flight height showing the strongest effect. Separate two-factor central composite design experiments were subsequently conducted for conventional Huanghuazhan rice, hybrid Yongyou 12 rice, Yangguang 131 rapeseed, and Stanley compound fertilizer. Material-specific quadratic models were established, yielding model-recommended flight height and forward speed combinations of 3.04 m and 2.35 m s−1, 2.79 m and 1.70 m s−1, 3.00 m and 1.80 m s−1, and 3.20 m and 2.25 m s−1, respectively. These combinations represent constrained model-based recommendations rather than global or independently verified optima. In a limited consecutive-pass field demonstration, the field-sample coefficient of variation (CVf) ranged from 13.76% to 20.34%, and the mean absolute pointwise deviation from the target count ranged from 15.11% to 19.05%. The results demonstrate the preliminary mechanical and operational feasibility of the prototype under the tested materials, operating settings, site, and environmental conditions.