# Analysis and Assessment of a Brushless DC Outrunner Motor for Agriculture Drones Using JMAG
## 3 Bldc Motor Analysis
### U12 KV 120 Motor Description  
The selected test motor was the outrunner U12 II KV 120 from T-Motor. It is a medium-end BLDC motor for heavy-lift aerial vehicles, with its basic parameters shown in Table 5. Its high power factor allows for future upgrades and improvements. Outrunner BLDC motors in agriculture drone applications typically have a long pole number and short length-diameter ratio to account for torque-demanding load requirements and relatively low speeds [16]. The 36-slot-42-magnet configuration of the test motor results in a small pole pitch, which reduces the electrical loss characteristic of larger diameters, while the superior split ratio ensures a high overall volume. The CAD design shows the rotor's greater axial length compared to the magnets (Figure 9). A yoke flux spreads to the cup material, thus increasing the effective magnetic area, allowing for thinner cup dimensions even when paramagnetic materials such as aluminum are used. The cross-sectional view of the motor reveals the rotational symmetry characteristic of salient pole designs; thus, a low winding inductance and reluctance torque is expected. The surface  
Figure 8: Boundary conditions: electric motor simulation. \begin{table}
\begin{tabular}{l c c} \hline \hline
**Parameter** & **Value** & **Unit** \\ \hline Velocity constant & 120 & rpm/V \\ Motor dimensions & 106.8 \(\times\) 47.6 & mm \\ Weight & 778 & grams \\ Internal resistance & 22 & mOhm \\ Magnetic configuration & 36N42P & - \\ Nominal voltage & 58.8 & V \\ Iddle current & 1.5 & A \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Motor parameters. magnet configuration allows for an air gap tolerance of 0.2 mm without compromising significant flux density. Motor manufacturers do not provide detailed material characteristics; some assumptions were needed for the simulation (see Table 6). The permanent magnet in the U12 II is the arc magnet N42 UH, with a radial magnetic pattern and a 1.5 mm width or 7.5 times the air gap length, as suggested by the literature. With a maximum working temperature of 180 \({}^{\circ}\)C and a remanence of 1.3 T. However, the working temperature should be kept below 120 \({}^{\circ}\)C to avoid significant demagnetization, as the magnetic hysteresis curve collapses over 80% on higher temperatures [17]. Figure 10 shows the winding configuration of the U12 motor. Concentrated winding reduces copper losses and allows for fault tolerance between coils, while its high cogging torque frequency translates into low cogging torque (Figure 11). Compared to a single winding layer, the double-layer winding reduces the increase in the conductor AC resistance as the frequency increases (Figure 12), by having 0.85 slots per magnet pole, and thus a coil span of 1 (Table 7). Shorter end-turn lengths can be used, reducing winding resistance and the overall motor volume. The definition of the coil placement in the slot region of the stator sets the back electromotive force (BEMF) ideally as a trapezoidal-shaped form. This BEMF is then softened by the conductor inductance and pole-to-pole leakage [18], resulting in a rounded, sinusoidal waveform (Figure 13). The low slot fill factor relates to the low KV (motor velocity constant) rating. While the use of higher conductor gauges increases the copper losses, the stranded parallel wiring reduces this effect and facilitates the winding process. Table 8 shows the typical KV range for large-sized UAVs in agriculture applications. Low KV is desired for vertical take-off configurations to achieve high efficiency at low speeds [19]. \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Value** \\ \hline Core & 50 CS600H \\ Magnets & Arc N42 UH \\ Conductor & Copper \\ Armature & Aluminum \\ Lamination factor & 95\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Motor materials. Figure 9: Three-dimensional CAD U12 II motor design. Figure 11: Cogging torque in the U12 II motor with 2548 rpm. Figure 12: Copper resistance evolution regarding source frequency. Figure 10: U12 II winding configuration.