Types of Motors

RoboCup 2019 Sydney
May 23, 2019

Choosing the motor you need among all types of motors can be a complicated task. Imagine that you are taking the first step toward doing a project while you are not sure about which motor to use, or even you have no information about different types of motors and there usages. You might have a product that you are not sure whether the motor it has is the right choice according to your needs or not. Whatever your goal is, here we have an introduction toward different types of motors which might help you dealing with such problems.

If you ask yourself, which motor and technology is better, you must know that the answer depends on the application and cost.

Here we try to present the whole picture of gear motors and the knowledge you need to choose the best one based on your need, so you would be sure about your selection.

Gear motor

A Gear motor is an electric motor. These gear motors make use of a gear system. Reducing design complexity and lowering the costs are good reasons for combining electric motor and gearbox. This combination is beneficial for motors built for high torque and low speed applications. 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.

Different Types of motors

types of motors

In selecting your gear motor first you must choose the type of gear motor you need. Gear motor is classified in different ways, but the primary distinction is whether you need a DC motor or an AC motor. This difference source is in the power source requirements of the motor. This difference can affect some performance factors such as cost, reliability, and speed control complexity.

AC Motors

 

“AC” stands for “Alternating Current”. Like other motors the usage of AC motors is to convert electrical energy into mechanical energy in order to do work in a system. The force of magnetic fields induced by alternating current flowing through electric coils is used for production of rotational energy.

AC motors properies

The first thing you must keep in mind is the phase, voltage, frequency, and current of the AC power available for the application.

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

Voltage, as 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, 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 describes the method of AC distribution.

Single-phase distribution, which involves one unison sinusoidal or other alternating voltage pattern, is used for standard commercial and residential power.

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. Three-phase power is most typically used for industrial or high power motors.

 

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 this type:

 

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

 

 

DC Motors

 DC Gear Motor

24 volt-200 RPM Buhler DC Gear Motor

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 over a wide range, using either a variable supply voltage or by changing the strength of current in its field windings. DC motors are the most common type of motors used in robotics, probably because These motors have a 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.

One major way of characterizing DC motors is based on brush type and brushless DC motors. This characterization refers to the manner of commutation used in motor, which converts direct current from the batteries into the alternating current required to generate motor action. If this commutation is performed mechanically with brushes, the commutator segments at the ends of the rotating rotor col physically slide against the stationary brushes that are connected to the terminals of motor. These type of motors are brush type DC motors. On the other hand for brushless motors, we see  a DC to AC conversion,that happens in the rotor electronically with position sensors and a microprocessor controller, so we need no brushes.

Pros and Cons

Brush type Pros

Certainly the primary advantage of brush type is the price,since the brush DC motor is cheaper than brushless one. Another advantage for this type is its easy understanding and simple design. Finally we can add quick start-stop acceleration to the list of advantages of this type.

Brush type Cons

Presence of brushes is the main disadvantage for this type, since the brushes wear down relatively quickly which leads to high maintenance costs. As a result the motor might not be able to operate well due to the hazardous conditions so the sparks might occur.

Brushless type pros

The long loge technology is one of the advantages. This type has little maintenance and high efficiency (85-90%).

Brushless type cons

These type of motors need higher initial costs.

The controllers are more complicated.

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 have mostly 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 is also reversed. 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, the current depends on the load, and increases with load. Therefore, it is important not to allow the motor to run with excessive loads that can stall it.
  • 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.

The GTFrobots site makes your choice easy. Just let us know if you need any of the above mentioned types of motors.

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