Electric Motors

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Categorized by many different means, the four main ways of categorizing electric motors are: the source of electric power, the internal construction, the type of motion they provide and their application. As a result, although electric motors can be divided into AC motors and DC motors (although universal motors that operate on both types of electrical currents tend to mess with that easy division) there are many more possibilities of categorization. Due to the wide range of electric motor types, there are a vast number of applications and industries that utilize them including: construction, in order to power varied machine and power tools; industrial manufacturing, used as industrial motors to power various manufacturing, processing and automation equipment; electronics, to power electrical devices such as hard drives, CD players, DVD players and more; residential, to power household appliances such as fans, clocks and exercise equipment; and office, for various equipment such as printers, computers and fax machines.

While all electric motors provide the same basic function of converting electrical energy to mechanical energy, the method by which they convert the energy can differ greatly. In terms of conversion methods, there are four main types of electric motors: servo motors, synchronous motors, induction motors and electrostatic motors, which are also referred to as capacitor motors. Servo electric motors operate based on a servomechanism (often shortened simply to servo) that utilizes error-sensing feedback to function and make corrections. Servo motors are extremely small electric motors and are often utilized in robotics, such as remote-controlled cars. Synchronous electric motors are a type of AC motor that operate based on a rotating magnetic field that is the result of the motor's rotor and current passing at the same rate. Much like synchronous motors are induction motors, which are fairly identical except that induction motors are asynchronous, even at times being referred to as asynchronous motors instead of induction motors. Induction motors operate based on the principle of electromagnetic induction in which a voltage is produces across a conductor, being the rotor, as it is moving through a magnetic field. Lastly, electrostatic motors are very different than the others, and instead operate based on the principle of the attraction and repulsion of an electric charge. Electrostatic motors are often used in very small-scale applications such as in micro-mechanical systems (MEMS).

Other than the method by which they convert electrical energy to mechanical energy, electric motors are also classified by means of the type of motion. Some common electric motors that fall under those classifications include: 3 phase motors, single phase motors, 12V motors, stepper motors and linear motors. 3 phase motors are typically a type of induction motor, and offer both high efficiency and a fairly simple design. 3 phase motors operate by means of a set of three alternating currents that are used to distribute the newly converted mechanical energy. Also commonly a type of induction motor, single phase motors operate based on a single-phase power source meaning that there is only one source of the electrical current, which is an AC. While still referring to the power source, 12V motors are categorized by the measurement of their power source and not the method of powering. One of the most common types of electric motors, 12V motors operate based on the standard 12 voltages of electric power. Stepper motors, on the other hand, are incredibly similar to three-phase synchronous motors. The main difference between those motors and a stepper motor is that stepper motors do not rotate continuously. Instead, stepper motors must continuously start then stop and start and then stop again and again. Finally, there are linear motors which are basically defined by the type, or really direction, of mechanical energy that they provide. Since a linear motion is motion that occurs over a straight line, linear motors can be defined as electric motors that provide motion over a single plane.

When categorizing based upon the construction of the electric motor, there are two main categories: brushed motors and brushless motors. Brushed electric motors can be easily determined based upon the design of the motor. A brushed motor is typically a type of DC motor, and operates based upon the actions of a wound rotor (also known as an armature), a commutator, and a permanent or wound magnet stator. The motor gets its name from the commutator, which is equipped with numerous brushes. These brushes operate by allowing the current to flow through them and thus arrive at the wound rotor. There are five main types of brushed motors: DC shunt wound motors, DC series wound motors, DC compound motors, permanent magnet DC motors and separately-excited motors. Capable of operation without the use of brushes to transfer the electrical current, brushless electric motors are also most often a type of DC motor. Whereas brushed motors can run into some problems due to their more complicated design, brushless motors eliminated many of those issues. Brushless motors consist of a permanent magnet external rotor, a three-phase coil, a type of sensor and drive electronics. Instead of brushes, brushless motors transfer the current by means of the sensors, called Hall effect sensors.

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Electric Motors Types

• 12V motors are a type of electric motor that operate based on 12 voltages, which are a unit of electrical force, of energy which they convert into mechanical energy to be utilized in the powering of various machinery or equipment.
• 3 phase motors are a type of electric motor that operates based upon a three-phase electrical load, which is a common form of electric power transmission.
• AC motors or alternating current motors generate their magnetic field by an electromagnet powered by the same AC voltage as the motor coil. It is dispersed in single or three-phase forms with the ability for direction changes of its current cycles.
  
• Brushed motors have built mechanical brushes that automatically commutate coils on the rotor as the motor rotates. Brush-type motors are more cost effective than brushless.
  
• Brushless motors allow commutation of the coils on the stator by using an outside power drive without brushes.
  
• DC motors or direct current motors have adjustable speed and torque applications. In a DC electric motor, there would be adjustable speed and torque along with a rotor and a permanent magnetic field stator.
  
• Electrical motors are motors that convert electric energy into motion using magnetism. Electric motors contrast engines because engines use fuel and electric motors do not.
  
• Gear motors consist of a gear head and motor.  Together they can reduce the speed of the motor to the preferred RPM's.
  
• Induction motors use electric current to generate rotation in the coils instead of delivering the rotation directly. They acquire their torque from currents produced in loops by a changing magnetic field in the field coils.
• Linear motor are a type of electric motor in which the converted mechanical energy provides motion to the equipment or machinery solely upon a single linear-axis.
• Permanent magnet motors have motor magnets embedded into the rotor assembly. This design allows them to align with the rotating magnetic field of the stator.
  
• Servo motors have shafts that do not rotate freely; the shafts move to a definite angular location. They are often used for motion control in robots, hard disc drives, etc. 
• Single phase motors are a type of electric motor that operate on single phase electrical power, which is a power source in which all of the voltages of the power supply in unison as a single unit, functioning to distribute alternating current (AC) power.
• Stepper motors are essentially electric motors without commutators. All of the commutation handled externally by the motor controller can be stepped at audio frequencies, allowing them to spin quite quickly and be started and stopped precisely at controlled orientations.
  
• Synchronous motors can operate at a constant speed up to full load. They have a series of three windings in the stator section with a rotating area; there is no slip.

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Electric Motors Terms AC (Alternating Current) - Current whose flow can be changed. Alternating current is commonly available in single and three forms.   Air Gap - The space between the rotor and stationary stator member in an electric motor.   Amps - The meter-kilogram-second unit of electric current that is equivalent to the steady current produced by one volt applied across a resistance of one ohm.   Armature - A part of the magnetic structure of a motor that rotates in a DC or universal motor.   Back End - The end that holds the coupling or driving pulley. Also referred to as the drive end.   Brush - Current conducting material that guides current from the power supply to the armature windings.   Commutation - Converting an electric current from direct current to alternating current. Can go both ways.   Core - The segment of the stator and rotor, usually iron, which is made up of cylindrical laminated electric steel.   Cycles per Second (Hertz) - One complete reverse of flow of alternating current per rate of time.   Duty Cycle - The duration and relationship of operating and non-operating times or repeatable operation at different loads.   Enclosures - The housing or frame of a motor in which there are two wide classifications: open and totally closed.   Endshield - The part of the motor housing that supports the bearing and acts as a protective guard to the electrical and rotating parts inside the motor. Often referred to as an "end bracket" or "end bell."   Fractional Horse-Power - A motor usually built smaller than that having a continuous rating of one horsepower. The frame size can categorize the motor as fractional also.   Front End - The end opposite the coupling or driving pulley. Also referred to as the commutator end.   Gearhead - A gearmotor part that holds the gearing, which converts the basic motor speed to the rated output speed.   Horsepower - A function of torque and rpm.   Jackscrew - A device used for the positioning of a motor. These are adjustable screws fitted on the base or motor frame.   Load - The burden forced on a motor by the driven machine. Often stated as the torque required to overcome the resistance of the machine it drives.   Motor - A device that takes electrical energy and converts it into mechanical energy to turn a shaft.     Relay - A device that is effective by a variation in the conditions of one electric circuit to affect the operation of other devices in the same or another electric circuit.   Rotor - Made of stacked laminations, it is the rotating component of an induction motor.   RPM - Revolutions per minute. The number of times per minute the shaft of the motor rotates.   Shaft - The rotating part of the motor that protrudes past the bearings for attachment to the driven equipment.   Stator - In an AC induction motor the stator is made of laminations with a large hole in the center for rotor to turn and slots in the stator for the windings to be inserted.   Torque - Force for turning provided by a motor or gear motor shaft. Often described in pounds.   Volts - The difference of possibility between two points in a conducting wire with a constant current of one ampere.

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