Due to factors such as a small amount of fertilizer application during rice topdressing and slow machine speed, the ordinary fertilizer discharge device fails to distribute the fertilizer uniformly and accurately as required, making it difficult to meet the needs of precise rice topdressing. This research focuses on the development of an offset spiral tooth fertilizer discharge device suitable for rice topdressing. The study analyzes the amount of fertilizer discharged in one cycle, the fertilizer force, and the motion of the fertilizer particles. In order to enhance the uniformity of the fertilizer discharge device at a low speed and small volume, the discrete element method is employed to conduct experimental research on the key structural parameters that affect the one-cycle amount of discharged fertilizer and the dynamics of the fertilizer discharge device. Through single-factor tests, it was found that the angle, height, number of spiral teeth, and diameter of the fertilizer discharge wheel are closely associated with the fertilizer discharge performance. To further investigate the impact of these four parameters on the fertilizer discharge performance, a regression combination test of the four factors is conducted based on the range optimized by the single-factor tests. A multi-objective mathematical model, considering the key parameters of fertilizer uniformity coefficient, one-cycle amount of fertilizer, and fertilizer discharge torque, is established at three speeds: 20, 55, and 90 rpm. The response surface method is utilized to analyze the influence of the interaction factors on the fertilizer discharge performance. The optimal combination of the key structural parameters was determined as follows: spiral tooth angle of 35.42°, tooth height of 9.02 mm, discharge wheel diameter of 57.43 mm, and tooth amount of 9.37. The bench test results of the device, using the optimal parameter combination and a fertilizer discharge speed of 0–90 rpm, were obtained for four commonly used rice fertilizers. The maximum variation coefficient of fertilizer discharge was found to be 10.42%. The one-cycle amount of fertilizer discharge was measured to be 19.82 ± 0.72 (A Kang), 17.20 ± 0.69 (Ba Tian), 20.34 ± 0.54 (Yaran), and 14.51 ± 0.44 (granular urea). The fertilizer discharge torque remained stable. These results indicate that the achieved optimization meets the precise fertilizer application requirements and can provide technical support for precise topdressing operations.

As a critical load-bearing system connecting the multi-rotor UAV airframe to the ground, the design quality of the landing gear directly affects flight safety and operational stability during takeoff and landing in complex environments. This paper presents a systematic review of the state-of-the-art in multi-rotor UAV landing gear design, with comparative references to fixed-wing alternatives where relevant. Beginning with an explicit, reproducible literature retrieval protocol, the study examines 86 peer-reviewed sources spanning 2014–2025. Structural configurations—including traditional fixed struts, telescopic landing gear, bio-inspired adaptive systems, modular designs, inflatable supports, and intelligent active-control architectures—are critically analyzed across diverse application scenarios, with particular emphasis on agricultural monitoring in paddy-fields. Key technical challenges are discussed in depth, including lightweight design, multi-environment adaptability, intelligent control, and advanced materials. In light of the specific requirements of agricultural UAVs during field operations, the paper evaluates cutting-edge research directions such as anti-rollover mechanisms, anti-sinkage capabilities, and non-destructive monitoring, supported by quantitative terrain–mechanics analysis. The review further expands the discussion of intelligent landing systems by detailing sensor-fusion architectures (vision, LiDAR, IMU/GNSS-RTK, soil-pressure transducers) and model-predictive adaptive-landing decision-making. Future development trends are outlined, proposing trajectories toward intelligentization, biomimicry, and multifunctional integration, thereby providing theoretical guidance for the optimization of landing gear design in precision agriculture.