Types of electric motor: Every electric motor works by running a current through a wire in a magnetic field. This produces a force. Because you want the motor to run continuously, you need to have a way of switching on the power to a wire to pull it towards the magnet, then turn off the power so it can rotate away again. There are two main types of electric motor used in electric bikes - the standard DC motor and the switched DC motor. Both run on direct current - that’s a supply with a positive and a negative terminal, unlike AC (alternating current). Standard DC motor: This motor has a series of wire coils on a spindle, rotating inside some fixed magnets. The current to the coils passes through some carbon brushes to the commutator - a series of metal plates on the rotating part of the motor. As the motor rotates, the brushes contact different parts of the commutator, and power passes through different coils. This way, the switching of the coils is completely automatic, and compensates for the speed of the motor without any extra circuitry.
Pros & Cons: The standard DC motor is very easy to control - there are just two wires, and you apply a fixed voltage to the wires to power the motor. The speed is proportional to the voltage. Very high torque is possible, but the motor is most efficient at high speeds, so a gearbox is necessary to reduce the speed to something useful for electric bikes. Because the brushes are rubbing continuously on the commutator, they can wear out - though with modern motors this takes a very long time. Switched DC motor: This motor is very simple - the coils are fixed, and the magnets rotate around them (or inside them). Sensors detect the position of the motor, and a computerised controller switches each coil on and off at the right point to turn the motor.
Pros & Cons: Switched DC motors can run at very low speeds, so they do not need a gearbox for electric bike use. This makes them simpler and cheaper than standard DC motors for electric bikes. But because there are only a few coils, the motor can be jerky at low speeds, and does not produce as much torque as a standard DC motor (unless you run it quickly and use a gearbox). The motor requires a dedicated controller, so the electronics are more complex, but there are no wearing parts. Who uses what, and why: Many cheaper electric bikes use switched DC motors, basically because they are very simple. No gears or bearings are needed, and the complicated electronics can be mass-produced on a microchip. Almost all more expensive electric bikes use standard DC motors, because of the high torque and reliability of these motors. Heinzmann use a very sophisticated standard DC motor, with the best bearings and gearbox that money can buy to make the motor very reliable. | 
