The Definition of Micro Motors
Micro motors generally refer to small-volume motors with an output power usually in the range of hundreds of watts. They are typically less than 100mm in diameter, or with power below 750mW, with voltage from 1-24V. The common micro motors are only a few millimeters in size, whereas micromotors in the hundreds of millimeters range are quite rare.
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Some kinds of Micro Motors
Structurally, a micro motor comprises a rotor, commutator, stator, and casing. In terms of fundamental principles, micro motors are made of magnets and coils in rotating devices, differing mainly in the magnetic fields created by the different current commutation of the coil, and in their distinct rotating structures.
DC motors and AC motors differ in their power sources; the former is driven by DC power while the latter is by AC power. Both operate through energized coils moving in a magnetic field. Micro DC motors are easier to control and suitable for applications requiring speed regulation.
Brushed motors and brushless motors differ in the method of commutation: brushed motors use friction between a carbon brush and a commutator for mechanical commutation, while brushless motors use sensors to determine the position for electronic commutation. Brushless motors are more costly, complex, quieter, and have longer service life.
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The Advantages of Micro Motors
Micro motors have high torque, low noise, small size, and are lightweight. They offer easy use, and constant speed, and can be paired with various gears to adjust output speed and torque.
Iron Losses in Micro Motors
Micro DC motors incur several types of losses during operation, and iron loss is one of them. Iron loss refers to the iron core in a permanent magnet DC motor losing some energy, due to being subjected to a fluctuating magnetic field. This lost energy is then dispersed either as heat or as noise.
Hysteresis Loss | When the magnetic field passing through the micro-motor core changes, the magnetic intensity of the core material changes. The movement of domain walls causes the tiny magnetic domains to expand and contract. During the movement, the domain walls may get stuck due to crystal defects, but eventually, they move, generating heat in the process. This is known as hysteresis loss.
Hysteresis loss can be represented by a hysteresis loop (B-H curve). The hysteresis curve is a closed loop, and the hysteresis loss of the material for one cycle of magnetic field change is the area within the hysteresis loop. If it’s an alternating magnetic field, then the size remains constant, and the energy loss per cycle is a fixed value. Hysteresis loss is directly proportional to frequency.
Eddy Current Loss | The core of a micro-motor is a conductor. Due to electromagnetic induction, changes in the internal magnetic field generate induced currents within the conductor, known as eddy currents. These eddy currents are perpendicular to the magnetic field, and their energy is dissipated as heat due to the resistance of the core material. Eddy current loss is directly proportional to the size of the current loop area and is related to the resistivity of the core material. If the core is made of very thin laminations with an insulating coating this can effectively reduce eddy current loss.