What are the Different Types of Motors?

RoboCup 2019 Sydney
May 23, 2019

Choosing the right motor among all types of motors can be a complicated task. Imagine you have decided to do a project but you are not sure which motor is the best option, or maybe you have no information about different types of motors and their usages. It’s even possible that you have bought some items and you’re not sure about the quality of its motor.

Whatever your goal is, in this article we’re trying to give you a general idea of what DC and AC motors are. with the knowledge you gain here, you can choose the best motor based on your needs and be sure about your decisions.  

 Types of motors

Electronic motors are divided into two main categories:

  • Ac motors (alternating motors)
  • Dc motors (direct motors)

These two motors have two distinct power sources. Different power sources can affect cost, reliability and speed control complexity.

Before diving into DC and AC motors, we need to talk about gear motors. simply put, a gear motor is the combination of a motor and a gear box. The specifying feature of this motor among all types off motors is that it produces high torque while maintaining a low horsepower, or low speed, motor output.

With this combination, there is no need to look for a specific gear box for your motor. Many roboticists use gear motors at 6, 12 and 24 volts. The main reason is that in robotic competitions, roboticists have to meet a specific requirements and with gear motors, they will no longer need to be worried about the adaptability of their motor and the gear box they have bought separately.

If you have decided to choose a gear motor, the first question that might rise is whether to choose a AC or DC motor. To make better decision between these two types of motors, lets dive into AC and DC motors.

AC Motors

“AC” stands for “Alternating Current”. Like any other motors, AC motors convert electrical energy into mechanical energy. Mechanical energy is what creates movement in different devices like washing machines or robots.  For production of rotational energy, the alternating current flowing through electric coils induce the force of magnetic fields.

AC motors properties

In order to choose an AC motor, the first thing you need to consider is the phase, voltage, frequency, and current of the AC power available.

Frequency:

the unit of frequency is Hertz (Hz) or cycles per second. frequency indicates the frequency of the oscillations of alternating current. 50 Hz is the most commonly used worldwide, but in North America uses 60 Hz. 400 Hz is a frequency used largely to power motors for aerospace applications.

Voltage:

voltage which is expressed in volts alternating current (VAC), can be delivered at many different levels. 110 VAC and 220 VAC are typical residential and commercial voltages, while power between 460 and 600 VAC is common for larger industrial applications. A small variation in voltage can have a dramatic effect on motor performance. Insufficient voltage reduces torque output and can keep a motor from sustaining its rated speed, while excess voltage increases torque which can cause damage during startup.

Current:

current is expressed in amps (A), describes the electrical current draw from motor at different points. Starting current, also referred to as locked rotor current, is the current draw when starting the motor. Starting current is always higher than full-load current. Full-load current indicates the current draw of the motor at its full rated output power.

Phase:

phase describes the method of AC distribution. Single phase power involves one unison sinusoidal or other alternating voltage pattern. Commercial buildings and residential homes use single phase power.

In contrast, three-phase power contains three simultaneous sinusoidal or other alternating voltage patterns, typically 120° out of phase with each other. Higher power efficiency and smoothness of operation is possible with three-phase operation. Industrial or high power motors uses three phase power

AC motors Pros and Cons

These types of motors are highly flexible in many features including speed control. Comparing to DC motors, they have a much larger installed base. Here are some key advantages of AC motor:

  • Low power demand on start
  • Controlled acceleration
  • Adjustable operational speed
  • Controlled starting current
  • Adjustable torque limit
  • Reduced power line disturbances

DC Motors

In DC Motors “DC” stands for “direct current”. This kind of motor converts direct current electrical energy into mechanical energy. The most common types rely on the forces produced by magnetic fields. A DC motor’s speed can be controlled by using either a variable supply voltage or by changing the strength of current in its field windings.

DC motors are the most common types of motors used in robotics due to large variety of shapes and sizes such as: permanent magnet iron core, permanent magnet ironless rotor, permanent magnet brushless, wound field series connected, wound field shunt connected, wound field compound connected, variable reluctance stepper, permanent magnet stepper, and hybrid stepper motors.

Common dc motors volts used in robots are as follows:

  • 6 dc motor
  • 12 volt dc motor
  • 24 volt dc motor

Types of DC Motors

Dc motors can be classified into two groups:

  • Brushed
  • Brushless

Brushed DC motors: in brushed dc motor, there is a brush and a commutator. The commutator segments at the ends of the rotating rotor slide against the stationary brushes that are connected to the terminals of motor, so the electricity can flow through windings.

Brushless DC motors: Brushless motors as the name suggests, do not have brushes. So in these motors, DC power converts to AC power with sensors and a microprocessor controller in rotor. In this way there is no need for brushes and commutators.

Brushed DC Motor Pros

  • The brushed DC motor is cheaper than brushless motor.
  • Another advantage of brushed motor is their simple and easy to understand design.
  • The last advantages of this motor is its start-stop acceleration.
  • High efficiency
  • High maintenance

Brushed DC Motor Cons

Brushed and commutators is the main disadvantages of these types of motors. The friction between the brushes and the commutator can easily make brushes to wear out which leads to high maintenance costs. As a result, worn brushes and commutators can cause sparking and motor failure.

  • higher initial costs
  • Complicated controllers

DC motors basic properties

Some important basic properties that you must consider while using a DC motor in a robotic or mechatronic project are direction, speed, voltage, current, power and torque.

  • Direction: DC motors mostly have two terminals. When the voltage is applied across these terminals, the motor starts to spin in one direction, and when the polarity of applied voltage is reversed, the direction of the rotation will also reverse. Thus, the polarity of applied voltage determines the motor direction, while the amplitude of voltage determines the speed of motor.
  • Speed: The speed of a motor, measured in rotations per minute (rpm), depends on the applied voltage and load.
  • Voltage: Each DC motor has a specified voltage that indicates the nominal voltage or the applied voltage that makes the motor run in its normal conditions. In practice, this nominal voltage is important in a project, since it indicates the maximum recommended voltage.
  • Current: When a motor is powered at the nominal voltage, by increasing current, the load will increase. Therefore, the motor should not run with excessive loads, because it can cause stalling.
  • Power: A motor’s power is the product of its voltage and current.
  • Torque: Torque is defined as the product of the force times the distance from the center of the shaft of a motor.

final words

As we discussed, there are two main types of motors: AC and DC motors. with what you have learned here, you can be confident about the decision you make. as we mentioned earlier, gear motors can have many benefits due to cost efficiency. So if you’re looking for DC gear motors, we’re offering 6v geared DC motor, 12v geared DC motor and 24v geared DC motor on our online store.

If you have any questions or any suggestions, leave us a comment and help us to be better.

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