## 6 Conclusions  
The UAV industry is a leading business for innovative growth, because it is a convergent industry of advanced technologies such as aviation, information and communication, and software. It is changing from low-cost and small-sized vehicles for simple filming to high-priced and medium-sized vehicles for various applications such as agriculture, surveillance, surveying, and delivery. Therefore, further studies should be conducted to improve the performance of the element parts and increase flight duration.  
In this study, electromagnetic field design and characteristic analysis were performed using an IPM motor instead of an SPM motor, a conventional UAV motor, by applying the finite element method to the UAV drive motor. IPM motors result in higher output power and efficiency with respect to the motor volume by using both reluctance torque and magnetic torque through phase angle control when compared to SPM motors. Therefore, an IPM motor, a high power and efficiency motor, could be applied to increase flight duration for medium- and large-sized UAVs for industrial or transportation purposes. In addition, the IPM motor was designed to ensure flight stability and performance by fabricating it in a hermetic case to prevent interference from external foreign substances during flight.  
A motor with a hermetic structure requires a low heat generation design because heat dissipation is important. Therefore, the heat dissipation characteristics were analyzed by designing the helical-grooved self-cooling case of the IPM motor. The performance was verified by experimenting with the heat dissipation characteristics with the case attached to the fabricated IPM motor. According to the geometric shape of the helical groove, a performance analysis was conducted using the diffusion equation for the water-cooled case. This could reduce the weight of the UAV and improve space use by cooling the motor without requiring a separate power source.  
In this study, the experiment was conducted after the case was mounted, and the results were compared with the experimental results of the conventional motor. Moreover, the thermal validity of the design was verified through the diffusion equation used. In the motor without the helical-grooved self-cooling, the temperature in each spot exceeded 100 \({}^{\circ}\)C, and the maximum temperature was 125.6 \({}^{\circ}\)C. In contrast, in the motor with the helical-grooved self-cooling, each temperature was below 100 \({}^{\circ}\)C, and the maximum  
Figure 13: Motor U-phase current comparison.  
temperature was 97.4 \({}^{\circ}\)C. The motor's output performance and efficiency were improved by enhancing the motor's mechanical performance and battery performance and reducing de-magnetization by suppressing the generation of hot spots of the permanent magnet inside the rotor.  
The cooling performance will be improved in future work by enhancing the heat dissipation of the lower part of the case and the outer part of the stator core, where the temperature is higher than that of other spots. Further studies are also planned to be conducted on increasing flight duration and battery efficiency by performing actual flight experiments by installing the motor on a UAV.  
Conceptualization, H.-S.L.; data curation, M.-H.H.; formal analysis, H.-S.L.; methodology, H.-S.L.; supervision, H.-R.C.; validation, M.-H.H.; visualization, H.-S.L.; writing--Original draft, H.-S.L.; writing--Review and editing, H.-R.C. All authors have read and agreed to the published version of the manuscript.  
This study has been conducted with the support of the Korea Institute of Industrial Technology as \"Development of Core Technologies for a Working Partner Robot in the Manufacturing Field\"(KITECH EO-21-0004)\".  
Not applicable.  
The authors declare no conflict of interest.