Linear motor

Most motors spin in a circle.

A linear motor is different. It moves in a straight line instead. This happens because the motor is unrolled.

It can push very fast trains. It can also start roller coasters. Some motors move things with great care. They help make small parts for machines. These motors are very useful tools. They help our world move.

Most motors spin in a circle. A linear motor is different. It moves in a straight line. This happens because the motor is unrolled.

There are two main ways these motors work. One way is called a linear induction motor (LIM). This type uses a moving magnetic field. The field hits a metal plate. This makes a new magnetic field inside the plate. The two fields push away from each other. This push creates motion.

Another way is the linear synchronous motor (LSM). This type uses magnets to move. It can be very fast and strong. Some LSMs are used for maglev trains. These trains float above the tracks.

Some motors are made for low speed. These are good for trains. Other motors are for high speed. These can launch things very fast. A coilgun is one example. Scientists even think about using them for spacecraft.

We use these motors every day. They power sliding doors on buses. They help robots move with great care. They even start some roller coasters!

A linear motor is a special kind of electric motor. Most motors spin in a circle to make things turn. A linear motor is different because it moves in a straight line. You can think of it as a regular motor that has been unrolled.

This unrolling allows the motor to create a straight push instead of a spin. Because they can move with great precision, they are used in millions of machines. In 2024, the market for these motors was worth 1.8 billion USD.

These motors work in a few different ways. One way is through a linear induction motor, or LIM. In a LIM, a moving magnetic field acts on a metal plate. This creates a second magnetic field inside the plate. These two fields push away from each other, which creates motion.

Another way is the linear synchronous motor, or LSM. An LSM uses an array of magnets on one side and a winding on the other. This design is great for moving things very quickly and smoothly.

People have been studying these motors for a long time. The history of linear motors goes back to the 1840s. A man named Charles Wheatstone worked on them at King's College London. His model was not very efficient for real work. Later, Alfred Zehden described a working induction motor in 1905. In 1935, an engineer named Hermann Kemper built a working model. Finally, Dr. Eric Laithwaite developed the first full-size working model in the late 1940s.

There are two main categories of these motors. Low-acceleration motors are used for ground transportation. For example, the Shanghai maglev train uses an LSM design. These are also used in some subway lines like the Toei Ōedo Line.

High-acceleration motors are much shorter and very powerful. They can launch objects to very high speeds. These include coilguns and railguns. Scientists even study them to help move spacecraft using mass drivers.

We see linear motors working in many parts of our lives. They are used in industrial robots and CNC machines to make things accurately. They can even power the sliding doors on many low-floor trams. Some amusement park roller coasters use them to start the ride.

They are even used in giant telescopes to move mirror segments. This helps the telescope stay perfectly aligned to see the stars. Whether it is a small robot or a huge train, these motors keep things moving.

A linear motor is an electric motor designed to produce a straight-line force. While most conventional motors are built to create rotational force, or torque, a linear motor is essentially an electric motor that has been "unrolled."

This design allows the motor to move along its length rather than spinning in a circle. These devices are essential for high-precision tasks and heavy transportation. In 2024, the market for these motors reached a value of USD 1.8 billion. They are used in millions of applications, ranging from tiny industrial robots to massive high-speed trains.

The fundamental mechanism often functions as a Lorentz-type actuator. In this process, the amount of force produced is linearly proportional to both the electric current and the magnetic field.

There are two primary ways these forces are generated. In a linear induction motor (LIM), a moving magnetic field acts on a conductor, such as an aluminum plate. This interaction induces eddy currents within the metal, which creates an opposing magnetic field according to Lenz's law. Because these two magnetic fields repel each other, the object begins to move as the field sweeps through the metal.

Another common mechanism is the linear synchronous motor (LSM). In an LSM design, an active winding is placed on one side of an air-gap, while an array of alternate-pole magnets sits on the other. These magnets can be permanent magnets or electromagnets. The rate of movement of the magnetic field is electronically controlled to track the motion of the rotor. This design is highly efficient for specific tasks. For example, high-precision industrial automation often uses a magnet stator paired with a moving coil. To ensure accuracy, a Hall effect sensor is often attached to the rotor to track the magnetic flux of the stator.

Linear motors are generally categorized by their acceleration capabilities. Low-acceleration motors are ideal for ground-based transportation, such as maglev trains. The Shanghai maglev train utilizes an LSM design for its propulsion.

These motors are often preferred for long-distance traction. Conversely, high-acceleration motors are designed to move objects to extremely high speeds over short distances. These include coilguns and the direct current homopolar linear motor railgun.

High-acceleration models are used in studies of hypervelocity collisions, as weapons, or as mass drivers for spacecraft propulsion.

The history of this technology spans nearly two centuries. The origins can be traced back to the 1840s with the work of Charles Wheatstone at King's College London. However, Wheatstone's early model was too inefficient for practical use. In 1905, Alfred Zehden of Frankfurt-am-Main described a feasible linear induction motor for lifts and trains. Later, the German engineer Hermann Kemper built a working model in 1935. The first full-size working model was developed in the late 1940s by Dr. Eric Laithwaite at Manchester University. His work eventually led to technologies used in the 1984 Air-Rail Link shuttle.

In industrial settings, linear motors offer significant advantages over traditional rotary or screw-driven systems. They provide direct-drive operation, which eliminates backlash and reduces the need for frequent maintenance.

They are used in CNC machining, semiconductor steppers, and high-speed robotics. These motors can achieve velocities of 2 m/s or more with micron-level positioning accuracy. Even in consumer infrastructure, they power sliding doors on low-floor trams and baggage handling systems. In massive scientific instruments, such as the European Extremely Large Telescope (ELT), hybrid actuators combine linear motors with piezoelectric elements. This allows for nanometer-level precision to keep mirror segments perfectly aligned.

Beyond industry and transport, these motors appear in unexpected places. Some modern roller coasters, such as Maverick at Cedar Point, use linear induction motors instead of traditional chain lifts to launch trains.

In the realm of space exploration, mass drivers are suggested as a way to accelerate cargo to escape velocity. However, high-acceleration motors face difficult design challenges. They require massive amounts of energy in very short periods. For example, one rocket launcher design requires 300 GJ of energy in less than a second. To meet these demands, engineers must use specialized energy storage like capacitors or homopolar generators.