How Do Motors Work and How to Choose the Right Motor?

Motors can be found almost anywhere. Here, fundamentals of electric motors, as well as the various types available and how to select the suitable motor are discussed. The basic issues to address when determining which motor is best for a given application are which type to select and which specifications are important. 

How do motors work?

Electric motors generate motion by transferring electrical energy to mechanical energy. The interaction of a magnetic field and winding alternating (AC) or direct (DC) current generates force within the motor. The magnetic field becomes stronger as the current strength increases. Remember Ohm's law (V = I*R): as resistance increases, voltage must increase to retain the same current. Electric motors are used in a variety of applications. Blowers, machine and power tools, fans, and pumps are common industrial applications. Motors are also used in tiny projects needing movement, such as robotics or modules with wheels. 

Types of motors:

There are many different types of DC motors, but the most common are brushed or brushless. Vibrating motors, stepper motors, and servo motors are also available. DC brush motors are among the most basic and can be found in a variety of gadgets, toys, and automobiles. To change the direction of the current, they use contact brushes connected to a commutator. They are inexpensive to manufacture, easy to manage, and offer excellent torque at low speeds (measured in revolutions per minute or RPM). Other disadvantages include the need for continual maintenance to replace worn out brushes, speed limitations owing to brush heating, and the generation of electromagnetic noise from brush arcing. 

Permanent magnets are used in the rotor assembly of brushless DC motors. They are widely used in the hobby sector for airplanes and ground vehicles. They are more efficient than brushed DC motors, require less maintenance, produce less noise, and have a higher power density. They can also be mass-produced and function similarly to an AC motor with a constant RPM, but are driven by DC current. Nevertheless, they are difficult to manage without a specialized regulator, and they require low starting loads and specific gears in driving applications, resulting in a higher capital cost, complexity, and environmental limits. 

  1. Vibrating motors: Vibrating motors are employed in vibration-sensitive applications such as cell phones and game consoles. They are caused by an imbalanced mass on the driving shaft, which is created by an electric motor. They can also be used in non-electronic buzzers that vibrate for sound, alarms, or door bells. 
  2. Stepper motors: Stepper motors are your best friend when it comes to accurate placement. They can be found in printers, machine tools, and process control systems and are designed for high-holding torque, allowing the operator to proceed from one step to the next. They have a controller system that specifies the position by sending signal pulses to a driver, who interprets them and sends proportional voltage to the motor. They are quite simple to build and regulate, but they always draw the maximum current. The short step distance limits top speed, and steps can be skipped under heavy loads. 
  3. Servo motors: Servo motors are another common hobby market motor that are utilized for non-precision position control. Remote control applications such as RC toy vehicles and robotics are among their most popular applications. They are generally controlled by pulse width modulation (PWM), which sends electrical pulses to the control wire and consists of a motor, a potentiometer, and a control circuit. AC or DC servos are available. AC servos are utilized for industrial machinery and can sustain bigger current surges, whilst DC servos are employed for smaller hobbyist applications. 

AC motors are classified into three types: induction, synchronous, and industrial.Asynchronous motors are those that do not move at the same constant pace or turn at a slower rate than the frequency supplied. Slip, the difference between actual and synchronous speed, is required in induction motors to produce torque, the twisting force that produces rotation. Induced current creates the magnetic field that surrounds the rotor of these motors. As AC is delivered, the rotor of synchronous motors rotates at a steady rate. Permanent magnets generate their magnetic field. Industrial motors are built for three-phase, high-power applications like conveyers and blowers.Home appliances and other applications that use AC motors include clocks, fans, and disk drives. 

How to Choose the Right Motor?

When choosing a motor, you need consider various factors, the most essential of which are voltage, current, torque, and velocity (RPM). 

  1. Voltage: Voltage is used to maintain net current in one direction and overcome back current. The torque increases as the voltage increases. A DC motor's voltage rating specifies the most efficient voltage while running. Make certain to use the recommended voltage. If you apply too few volts, the motor will not operate, but too many volts can short the windings, resulting in power loss or total damage.
  2. Current: The motor is powered by electricity, and too much current will harm it. The operating and stall currents of DC motors are critical. The operating current is the average amount of current that the motor is predicted to draw under normal torque conditions. Stall current generates enough torque to allow the motor to operate at stall speed, or 0RPM. This is the maximum current and power that the motor should be able to draw when multiplied by the rated voltage. Heat sinks are required when the motor is constantly running or when the voltage is higher than the rated voltage to keep the coils from melting.
  3. Torque: Torque must also take into account operating and stall values. Operational torque is the torque that the motor was designed to produce, whereas stall torque is the torque produced when power is introduced from stall speed. Although the needed operating torque should always be considered, some applications will demand you to know how far you can push the motor. For example, with a wheeled robot, good torque equals good acceleration, but the stall torque must be powerful enough to lift the robot's weight. Torque is more crucial than speed in this case. 
  4. Velocity: When it comes to motors, velocity or speed (RPM) might be complicated. The general rule is that motors perform best at high speeds, however this is not always practicable if gearing is required. Increasing gears can affect motor efficiency, so consider speed and torque reduction as well. 

These are the fundamentals to consider while purchasing a motor. To choose the right sort of motor, consider the application's function and the current it uses. The characteristics of an application, such as voltage, current, torque, and velocity, will determine which motor is most appropriate, so pay attention to them.

Prasun Barua

Prasun Barua is an Engineer (Electrical & Electronic) and Member of the European Energy Centre (EEC). His first published book Green Planet is all about green technologies and science. His other published books are Solar PV System Design and Technology, Electricity from Renewable Energy, Tech Know Solar PV System, C Coding Practice, AI and Robotics Overview, Robotics and Artificial Intelligence, Know How Solar PV System, Know The Product, Solar PV Technology Overview, Home Appliances Overview, Tech Know Solar PV System, C Programming Practice, etc. These books are available at Google Books, Google Play, Amazon and other platforms.


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