Technical-motor and drivetrains
The two most common hub motors used in electric bicycles are brush motors and brushless motors. There are many configurations to choose from, varying in cost and complexity; both direct drive and gear motor units are used. The power assist system can be added to almost any pedal cycle using chain drive, belt drive, hub motor or friction drive. Brushless DC hub motors are a common modern design. The motor is built in the hub, the stator is firmly fixed on the axle, and the magnet is connected to the wheel and rotates with the wheel. The hub of a bicycle is a motor. The power level of the motor used is affected by the available legal category and is usually, but not always, limited to 750 watts.
Another type of electric auxiliary motor, commonly referred to as an intermediate drive system, is gaining popularity. In this system, the electric motor is not built into the wheel, but is usually installed near the bottom bracket shell (usually below). In a more typical configuration, the gear or wheel on the motor drives the belt or chain and meshes with a pulley or sprocket fixed to the crank arm of the bicycle. Therefore, the driving force is provided by the pedals instead of the steering wheel, and is finally applied to the wheels through the bicycle's standard transmission system.
Since power is applied through chains and sprockets, power is usually limited to around 250-500 watts to prevent rapid wear on the drive train. The combination of the electric intermediate shaft and the internal gear hub at the rear wheel hub may require care because of the lack of a clutch mechanism to reduce the impact on the gear when re-engaged. A continuously variable transmission or a fully automatic internal gear hub can reduce the impact caused by the viscosity of the oil used in the mechanical coupling of the liquid coupling instead of the traditional internal gear hub.
