## 5 Environment and Results of the Experiment on Heat Dissipation Characteristics
### Heat Dissipation Characteristics: Experimental Results and Comparison  
In this experiment, the temperature inside the motor and the loss of the motor were measured and examined over time while constantly rotating at a certain speed. Conventional commercial motors were also measured and tested to verify the prototype, comparing the results. The experiment was conducted under rotating at a constant speed condition of 3000 rpm with a propeller mounted. The performance characteristics and temperature of the motor were measured at 0.5 s intervals. The experimental results of the heat generation characteristics with and without the helical-grooved self-cooling case on the designed and fabricated UAV motor are shown in Figures 10 and 11, respectively. The model without the water-cooled cooling structure is motor A, while the model with the structure is motor B. \begin{table}
\begin{tabular}{c c} \hline \hline
**Thermocouple Wire** & **Location** \\ \hline Spot 1 & Coil \\ Spot 2 & Top of stator inside \\ Spot 3 & Bottom of stator inside \\ Spot 4 & Top of stator outside \\ Spot 5 & Bottom of stator Outside \\ Spot 6 & Inner Bottom Cover \\ Spot 7 & Outer Bottom Cover \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Main parameter of the stator. Figure 8: Configuration of the UAV motor heat dissipation characteristics experiment. Figure 9: Thermocouple wire attachment location. The temperature distribution of the motor for each spot was 77.2-97.4 \({}^{\circ}\)C for motor A, and 73.6-125.6 \({}^{\circ}\)C for motor B when the temperature was saturated, and a particular temperature range was reached. It was found that the temperature of motor B, where the cooling oil circulated and dissipated the generated heat, was 28.2 \({}^{\circ}\)C lower than that of motor B.  
Figure 11: Heat dissipation experimental results of motor B.  
Figure 10: Heat dissipation experimental results of motor A.  
motor A, based on the maximum temperature. In particular, the temperature difference was high in the coil and stator, which are the main heat sources. Moreover, the temperature of the main heating source of motor A exceeded 100 \({}^{\circ}\)C, while the temperature of each spot in motor B was below 100 \({}^{\circ}\)C. Therefore, the mechanical performance of the motor and battery performance improved by dispersing the temperature of the main heat source. Demagnetization was reduced to prevent the strength of the magnetic force from deteriorating by suppressing the hot spot generation of the permanent magnet inside the rotor. Furthermore, although the temperature was distributed in spots 1, 5, 2, 4, 3, 6, and 7 in motor A, the order was changed to spots 1, 2, 3, 4, 5, 6, and 7 in motor B. The temperature of spots 4 and 5 near the coil decreased, thereby lowering the temperature of the stator core. This prevents damage due to a large amount of heat by the eddy current being generated in the stator core while ensuring consistently stable operability. Figure 12 presents a comparison of the temperature values at 15 min, which is the temperature of saturation. The temperature of the coil, which is the maximum source of heat, was 126.1 \({}^{\circ}\)C for motor A and 95 \({}^{\circ}\)C for motor B. Thus, the temperature was reduced by 31.1 \({}^{\circ}\)C; moreover, the temperature decreased at all spots by an average of 11.63 \({}^{\circ}\)C, excluding spot 6 which presented a high temperature because it was a place where cooling oil was sprayed. Therefore, the heat generated by the motor dispersed, and the total temperature inside the motor decreased. Figure 13 shows a graph comparing the current while the motor was being operated, measuring at 1 min intervals. The temperature remained constant from 0 to 5 min. However, there was a large deviation in the current in the subsequent section, and the maximum deviation was 3.13 A. This is because motor A did not smoothly cool the coil and the stator core, whereas motor B maintained the strength of the magnetic force by cooling and dissipating heat.