## 3 Performance Comparison of the Proposed and Other Models  
Table 2 presents the comparison results for the back EMF and torque according to the vernier motor classification, including the SPM vernier motor, rotor-half, stator-half, and DHPM-type vernier motors. The back EMF and torque of the stator-half PM-type vernier motor are much lower than those of the SPM vernier motor. The DHPM vernier motor attempts to increase motor performance by installing additional PMs in the slot to combine the electromagnet's MMF with that of the PM. However, as listed in Table 2, some performance improved but not satisfactorily. In other words, the best performance is exhibited by the DHPM vernier motor that has added PMs to the stator in the structure of the rotor, which was replaced by salient poles to reduce the PMs by half. However, the model has not achieved satisfactory performance due to the short-circuit flux. Thus, we chose this as a comparative model and proposed a new concept model. Comparison of Specifications of the DHPM-Type Vernier Motor for the Proposed DHPM Vernier Motor and Compatible Model  
Table 3 lists the specifications for the proposed models. If the inclination angle is 0\({}^{\circ}\) for the conventional model [11], the proposed model has the same structure except for the inclination angle, 7.5\({}^{\circ}\). However, due to the three-phase alternating current flows, the polarity and strength of the electromagnet vary depending on the phase angle. Nevertheless, the polarity of the PM remains fixed. Therefore, the motor performance cannot be improved as expected due to a large magnetic short circuit. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Items**} & \multicolumn{4}{c}{**Classification of the Vernier Motor**} \\ \cline{2-5}  & **SPM** & **Rotor Half** & **Stator Half** & **Double Half** \\ \hline Back EMF [V] & 1.24 & 1.18 & 0.26 & 1.68 \\ Torque [N-m] & 2.42 & 2.40 & 0.49 & 3.85 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison results of the double half permanent magnet (DHPM)-type vernier motor with typical surface permanent magnet (SPM), rotor-half PM, and stator-half PM motors. As presented in Table 2, the comparison model has better performance than the other models. We cannot achieve the expected effect of increasing the magnetic flux density using PMs in the stator due to magnetic flux short circuits. The saddle coil in a motor designed with the new concept is used to minimize the motor volume with a typical cylindrical structure. The new idea for this motor is to design the stator exterior with a slope in the direction of the motor length, as depicted in Figure 2. We can reduce the volume in the designed motor compared to conventional motors, as displayed in Figure 1. This reduction is due to shortening the length of the stator's magnetic circuit, causing a reduction in magnetic resistance to the magnetic circuit and resulting in more efficient use of the magnetism generated by the coils installed in the stator. When the coils are winding in the stator in the newly designed motor, the shape is different from that of a conventional cylindrical motor. If the coil winding direction within the slot is on the \(z\)-axis, the stator has a new design with an inclination angle between 0 and \(x\) degrees. Thus, the coil height around the slot using this angle increases linearly, resulting in the same shape of coil winding around the slot core of the teeth part as that of the saddle. However, a typical cylindrical motor has the same height status of the coils between \(z=0\) and \(z=x\) when observed in the length direction. The maximum external diameter of the newly proposed motor is the same as that of the predecessor model. Therefore, the stator's outer diameter is sloped and reduced compared to that of the predecessor. Thus, the wound coil width is reduced. The coil width can be decreased, whereas its height increases, resulting in an overall saddle shape.