A new type of stator design and arc shaping method that is used in a diametrically wound and diametrical air gap type of brushless motor. After arc shaping, the stator of this brushless motor has an external profile composed of a central arc and two modified arcs located on each side of the central arc. The central arc subtends an angle twice that of angle A and the modified arcs each has a radius r, both angle A and r are given by the following formulae: ##EQU1## Through arc shaping the stator, the cogging torque is lowered while a certain standard value for the torque constant is still maintained. Thus, the overall efficiency of the brushless motor is raised.