Generally, the motor is rotating when it works. But vehicles driven by rotating motors (such as electric locomotives and city cars) need to move in a straight line, as do some parts of machines driven by rotating motors. This required the addition of a set of devices to convert rotational motion into linear motion. Can it be driven directly by a linear motor, thus eliminating the set? This question was raised decades ago. The linear motion motor is now made, that is, the linear motor.

The principle of linear motor is not complicated. Imagine a rotating motion of the induction motor along the direction of the radius of open, and flattened, this becomes a linear induction motor. In linear motor, equivalent to the rotating motor stator, called primary; Equivalent to rotating motor rotor, called secondary. The primary communicates, and the secondary moves in a straight line along the primary under the action of the electromagnetic force. The primary has to be very long, extending to where the movement needs to be, while the secondary doesn't have to be that long. In fact, the linear motor can make the primary very long, also can make the secondary very long; It can be either primary fixed or secondary mobile, or secondary fixed or primary mobile.

Linear motor is a new type of motor, which has been widely used in recent years. Maglev trains are driven by linear motors.

Maglev train is a new kind of train. The average train, due to friction between the wheels and the rails, limits its speed, and can reach a maximum operating speed of no more than 300km/n. Maglev trains use magnets to levitate the train and remove it from the guide rail to reduce friction and increase speed. Trains are drawn by linear motors. One stage of the linear motor is fixed on the ground and extends to the distance with the guide rail; Another stage is installed on the train. When the primary communication is communicated, the train moves along the guide rail. The train is equipped with magnets (some are coils that also use linear motors). When the magnets move with the train, the coils (or metal plates) on the ground will generate an induced current. The magnetic field induced by the current and the electromagnetic force between the magnets (or coils) on the train will suspend the train. The advantages of the hover train are smooth running, no turbulence, low noise, little traction required, only a few thousand kw power can make the hover train speed of 550km/h. When the suspension train slows down, the change of magnetic field decreases, the induced current also decreases, and the magnetic field weakens, resulting in the decrease of suspension force. The hovertrain is also equipped with wheels, which, like an airplane, pull into the train as it moves and can be lowered to support it when it stops.

To magnetically levitate a massive train requires a strong magnetic field, which in practice would be generated by high-temperature superconducting coils.

Besides maglev train, linear motor is also widely used in other aspects, such as transmission system, electric hammer, electromagnetic stirrer and so on. In our country, linear motor has also been popularized and applied. Although the principle of linear motor is not complicated, it has its own characteristics in the design and manufacturing. The product is not as mature as the rotary motor and needs to be further studied and improved.