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Types of small motors

Types of small motors
   Last Modified:    Published: 2022/08

Motors can be classified based on a wide range of characteristics, from the power source to structure, size, power output, and application. Of these, small and micro motors (sometimes called ultra-small motors) are used in a wide array of precision equipment, robots, and other cutting-edge fields.

Brushed, brushless, and coreless motors

Motors can be classified as AC motors or DC motors depending on the type of power supply. AC motors use alternating current as a power source. They are often large and used in industrial applications such as pumps and conveyors in logistics. They can also be found in larger home appliances and electric vehicles. DC motors tend to be smaller in size. They are powered by direct current and are used in smaller home appliances, radio control models, and electronic devices.

There are two main types of DC motors: Brushed and Brushless

Brushed DC Motors

Brushed DC motors consists of a rotor made of a copper wire coil and a magnetic stator. The end of the coil is connected to the commutator, which creates the contact point. The commutator is able to rotate while maintaining contact with the brush. DC current flows through the brush. When the commutator and the brush come into contact, electricity flows into the coil, creating a magnetic field that either repels or attracts the stator, causing the rotor to rotate. As the rotor rotates, current flowing through the coil alternates between attracting and repelling, keeping the rotor in motion.

Brushed DC motors have a simple structure and do not require a drive circuit. They are easy to handle, but since the brush and the commutator are in physical contact with each other, wear and tear are inevitable. Brushes may need to be replaced on a regular basis. Mechanical noise and electrical noise, such as from sparks, are also likely to be generated at the contact points.

Brushless DC Motors

Brushless DC motors eliminate the brushes and commutators. They are equipped with only the magnetic rotor and the stator with coils. The stator can be arranged around the rotor as the core, or the rotor can be placed around the stator. To generate movement, a drive circuit that switches the current flow to the coil is required.

If the stator, with its heat-producing coil, is located around the exterior of the motor, heat can dissipate easily, helping the motor stay cool and perform at its best. Since brushless motors have no contacting parts, there is no wear and tear or need for maintenance. These motors have long lifetimes. And because there are no electrical contacts, high currents can be applied to produce large power outputs, all while suppressing the generation of noise. Motors can also be categorized by internal configuration: coreless motors, geared motors, and others.

Coreless Motors

Among the brushed DC motors, those that do away with a core of wire coil that forms the rotor are known as coreless motors. The rotor is made by forming the copper wire into not a coil but into a basket shape. A magnet is placed inside the rotor and the rotor rotates around the magnet.

Since there is no core, the rotor is lighter and the moment of inertia is greatly reduced, leading to motors with improved startup and response times. In addition, since there is no metal core, cogging, which occurs when the core and magnet attract each other, does not occur, and the motors run smoothly with less vibration and noise. Since the rotor is comprised of only the coil, the motor itself can be made smaller and lighter.

Geared Motors

Geared motors integrate reduction gears in the rotation shaft. The reduction gear enables lower-speed rotation with higher torque than is achievable with typical motors.

Applications of small motors and the expertise necessary for their production

Motors are also categorized by their power output. Motors with small outputs are called small motors. Generally, motors with outputs less than 75 W are categorized as small motors, and those with outputs less and 3 W are categorized as micro motors sometimes referred to as micro motors. The power required to operate them is also small and they can be operated with standard batteries. AC motors require 100 V or higher power and have risks such as electrical leaks and generation of sparks, which can ignite fires. DC motors are often used to avoid these risks when appropriate.

Hollow shaft micro motor

Micro brushless motors with an outer diameter of less than 1 mm have been developed. Using advanced microfabrication techniques, geared motors comprised of very small motors and integrated gearing mechanisms that are only a few millimeters in size have been made.

These small motors have various applications such as in audiovisual equipment, medical equipment, communications equipment, measuring instruments, and robots. For robots, servomotors that use small, high-power motors are often used to drive joints. Small motors that have low power consumption, and respond quickly and accurately are used in small devices such as portable cassette recorders and cameras. Of these small motors, the hollow shaft motor, in which the rotating shaft is hollow, is used for mounting heads and micro manipulators where wiring space is very limited. Since cables such as optical fibers can be passed through the shaft, it is also possible to construct micro actuator mechanisms.

Since the internal components of small motors are also very small, high performance is required from each component in order to obtain high torque and stable rotation. For example, magnets that are small and thin, yet generate high magnetic force, and coils made of ultra-fine wires that are wound tightly are essential for making small motors that produce high torque and have low power consumption. To accomplish this, the technology to make strong magnets, wire winding know-how, and winding machine technology are required. In addition, each mechanical component used in a small geared motor may be submillimeter in size, requiring the use of new materials and mastery of injection molding technology using precision molds.

Orbray's product lineup of small motors (under φ30mm) and peripheral devices helps meet demands for smaller, thinner devices, high power output, and energy efficiency.

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