Selection of a Brushless DC Motor Employed to Propel an Electric Car

This work presents the results of the development of a small electric car and the study of a Brushless DC Motor, employed to propel the electric car. The aim was selecting a motor with characteristics of operation suited to propel the electric car at a speed from 12 to 20 km/h. The propulsion system has a brushless DC motor and an electronic control unit. The electronic control unit was designed and constructed based on the characteristics of the selected brushless motor. Tests were carried out on the electric car, with the purpose of determining the behavior of the mechanical power required by it, as a function of speed. The results allowed selecting a brushless motor with the following characteristics: 12 V, 5.9 A and 13600 rpm. A theoretical study was developed to determine the suited gear ratio between the speed of the motor and the speed of the wheels of the car. Theoretical values of mechanical power developed by the brushless motor, computed as function of the battery voltage and of speed, were compared to the values of mechanical power required by the car, obtained by means of tests. By doing that, it was possible to calculate the characteristics of operation of the brushless motor in which it develops its maximum efficiency, when it propelled the electric car. The gear ratio resulted in 64:1. The study showed that the car would require a mechanical power of 58 W, when it was at 20 km/h.