# Analysis and Assessment of a Brushless DC Outrunner Motor for Agriculture Drones Using JMAG
## 1 Introduction  
High-efficiency electric machines have gained significant interest in modern technological industries, such as automation and robotics, home appliances, and electromobility, where electric motors represent over half of the electricity expenses and about two-thirds of the total power consumption. Out of the vast catalog of electric machines,the brushless permanent magnet motor (PM motor), characterized by an electronically controlled commutation stands out by its high torque density, good efficiency, and versatility. The use of PM motors in appliances is supposed to provide up to a 42% energy reduction, compared to conventional alternating current motor appliances, and its implementation in ground and aerial vehicles allows for high power efficiency at low speeds. Multi-copter Unmanned aerial vehicles (MUAV) are used in various fields for their hovering capabilities and maneuverability [1]. However, these precise characteristics make them the least efficient aerial robot by depending entirely on actuators to generate lift. On the other hand, modern battery technology imposes limitations on flight time, negatively impacting all drone applications. The propulsion system, directly relates to the efficiency and performance of the vehicle. A lot of effort in early drone design is consequently directed towards designing and selecting the ideal elements for the desired operating range, commonly executed empirically by testing multiple element combinations [2]. In large-sized MUAVs, a high torque-to-weight ratio and efficiency make the brushless DC motor (BLDC) the preferred PM motor. Its typical rectangular wave-formed current reproduces electronically the physical brushes characteristic of the direct current (DC) motor, thus producing an alternating current (AC) signal to operate, making it fundamentally an AC machine. This driving technique allows for considerable energy loss reduction and broader commutation options for specific applications. This flexibility comes at the expense of driving complexity, requiring an electronic speed controller (ESC) to operate [3]. The ESC includes the power electronics, rotor position detection methods, and controllers needed to generate the trapezoidal commutation commonly used in low- and medium-end agriculture unmanned aerial vehicles. Several works address the design and analysis of BLDC motors. In [4], electromagnetic analysis in a switched reluctance, induction, and BLDC motor using _ANSYS Maxwell_ software was conducted. The BLDC motor proved to be the most efficient and offered the highest torque density in the desired operating range. The differences in inner and outer brushless motors were discussed in [5], highlighting the superior power-to-weight ratio and torque density of outrunners, making them ideal for agriculture UAV applications where high inertia and low to medium speeds are desired. The electromagnetic radial flux property of BLDC motors allows for a good field distribution and reduced dimensions, while their surface magnet rotor structure, typically found in drones, offers mechanical simplicity and improved controllability. Recent works focus on the multi-step analysis and optimization of electric machines using important geometric characteristics as input parameters. The finite element method is used for pre-manufacture output evaluation, with particular interest in efficiency, torque, and output power. In [6], the influence of magnet geometry on cogging torque is investigated. Through the use of both analytical and numerical methods, the most influential motor harmonics are weakened through eccentric magnet shapes, effectively reducing torque ripple up to 90 percent, resulting in quieter and less fault-prone motors, while in [7], a novel back-electromotive-force detection method is presented. The improved technique allows for a full motor operating range and smooth start, by combining two different sensorless detection methods. Few works address the analysis of BLDC motors for drone design purposes.