A motor is a device that converts electrical energy into mechanical energy.  It operates based on the principles of electromagnetism.  When electric current flows through a coil of wire placed within a magnetic field, it generates a force that causes the coil to rotate, thereby producing mechanical motion.  Motors are widely used in various applications, including industrial machinery, household appliances, vehicles, and robotics, among others.  They come in different types, such as AC motors (alternating current), DC motors (direct current), stepper motors, and servo motors, each suited to specific purposes and requirements.

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Motor Index

• Motor Design Classification
  • DC Motor
  • AC Motor
• Motor Glossary

 Motor Design Classification

• DC Motor  -  A type of electric motor that operates on DC electricity.  It converts electrical energy into mechanical energy through the interaction of magnetic fields.  DC motors operate on power where the current flows in one direction such as the power generated from batteries or AC power sources that are rectified to direct current.  The two major categories of DC motors are brushed and brushless, for more information on specifics of brushed and brushless motors, visit here:
  
  • Brushed  -  A type of DC electric motor that operates using brushes and a commutator.  It's one of the simplest and most common types of electric motors, widely used in various applications such as household appliances, power tools, toys, and automotive systems.  This motor has permanent magnets inside its outer body with a rotating armature inside.  The permanent magnets are stationary and are called the stator.  The rotating armature contains an electromagnet and is called the rotor.
    
    • Shunt Wound
      
    • Separately Excited
      
    • Series Wound
      
    • Compound Wound
      
    • Permanent Magnetic
      
    • Servomotor
      
    • Universal
      
  • Brushless  -  An electric motor that operates on DC and does not rely on brushes and a commutator for operation, unlike traditional brushed DC motors.  Instead, BLDC motors use electronic commutation to control the stator windings, making them more efficient, reliable, and maintenance free compared to brushed DC motors.  Like a brushed motor, a brushless motor works by alternating the polarity of windings inside the motor.  It is essentially an inside out brushed motor, which eliminates the need for brushes.  In a brushless DC motor, the permanent magnets are fitted to the rotor, with the electromagnets on the stator.  An electronic speed controller regulates or commutates the charge to the electromagnets in the stator, to enable the rotor to travel through 360-degrees.
• AC Motor  -  An electric motor that operates on AC electricity.  Unlike DC motors, which operate on direct current, AC motors rely on the changing polarity and direction of the electrical current to generate the rotating magnetic field necessary for producing mechanical motion.  These motors are powered by single or three phase alternating currents. The electromagnetic field in the stator reacts with the rotor and causes the motor to rotate at a synchronous speed to match the frequency of the AC current.  AC motors are efficient, durable, quiet, and flexible, which makes them a viable solution for many power generation needs.
  

• • Induction Motor  -  An induction motor is a type of AC electric motor.  It's one of the most commonly used types of electric motors due to its simplicity, reliability, and robustness.  Induction motors operate on the principle of electromagnetic induction.  Almost all induction motors run at essentially constant speed from no-load to full-load conditions.  The speed of induction motors depends on the supply frequency and hence these motors are not easily adapted to speed control. Induction motors are simple and rugged in construction, less expensive, easy to maintain, and can be designed and produced with characteristics to suit most industrial requirements.
    
    • Squirrel Cage  -  Also called an induction motor, is a type of AC electric motor widely used in various applications due to its simplicity, reliability, and robustness.  The name "squirrel cage" refers to the rotor design, which resembles a rotating cage.  The shaft is connected to the rotor which looks like a cage and it works on the principle of electromagnetism.  So it uses the electromagnetic induction effect to convert the electrical energy into rotational energy.
      
      • Single Phase
        • Shaped Pole
        • Split Phase
          • Capacitor Start
          • Capacitor Start (Permanent -Split Capacitor)
          • Capacitor Start/Run
          • Resistance Start
      • Three Phase
        • Design A
        • Design B
        • Design C
        • Design D
    • Wound Rotor  -  Also called a slip ring motor or wound rotor induction motor, is a type of AC electric motor that shares similarities with squirrel cage induction motors but has a distinct rotor design and additional features for enhanced control.  A wound rotor induction motor is defined as a special type of 3 phase AC induction motor designed to provide high starting torque by connecting an external resistance to the rotor circuit.  The motor’s rotor is a type of wound rotor.
      
      • Single Phase
        • Repulsion
          • Repulsion Start
          • Repulsion Induction
      • Three Phase
        • Three Phase Round Rotor
  • Synchronous Motor  -  It is another type of AC electric motor, distinct from induction motors.  Unlike induction motors, synchronous motors operate at a constant speed that is precisely synchronized with the frequency of the AC power supply.  The rotation of the rotor (or shaft) is synchronized with the frequency of the supply current.  That is, the rotation period of the rotor is equal to the rotating field of the machine it is inside of.
    
    • Single Phase
      • Reluctance
      • Sib-Synchronous Reluctance
      • Hysteresis
      • Stepper
        • Permanent Magnet
        • Variable Reluctance
        • Hybrid
    • Three Phase
      • Permanent Magnet
      • Synchronous Reluctance
      • Hysteresis
      • Synchronous Induction
  • Linear Motor  -  A type of AC electric motor that produces linear motion instead of rotational motion.  It operates on the same principles as traditional rotary AC motors but is designed to generate linear movement along a straight path.  In a traditional electric motor, the rotor spins inside the stator, in a linear motor, the stator is unwrapped and laid out flat and the rotor moves past it in a straight line.  Linear motors often use superconducting magnets, which are cooled to low temperatures to reduce power consumption.
    
    • Induction
    • Synchronous

Motor Glossary

A

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• Actuator  -  A device that creates mechanical motion by converting various forms of energy to rotating or linear mechanical energy.
• Alternating Current  -  An electric current that periodically reverses direction, typically at a rate of 50 or 60 cycles per second (Hz).  This reversal of direction produces a sinusoidal waveform that can be used to transmit electrical power over long distances.
• Amortisseur Winding  -  Pole face bar windings embedded in the cores of the field poles of synchronous machines; used to dampen rotor oscillations, and as a squirrel cage winding for starting synchronous motors.  Also termed damper winding.
• Armature  -  The rotating part of a brush type direct current (DC) motor.  In an induction motor, the rotating part is called a rotor.

B

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• Backlash  -  This is the typically undesirable quality of "play" or "slop" in a mechanical system.  Gearboxes, depending on the level of the precision of the parts and the type of gearing system involved can have varying degrees of backlash internally.  Usually expressed in thousandths of an inch and measured at a specific radius at the output shaft.
• Base Speed  -  Base speed is the manufacturer’s nameplate rating where the motor will develop rated HP at rated load and voltage.  With DC drives, it is commonly the point where full armature.
• Brush  -  Current conducting material in a DC motor, usually graphite, or a combination of graphite and other materials.  The brush rides on the commutator of a motor and forms an electrical connection between the armature and the power source.
• Brushed Compound Motor  -  A combination of the brushed shunt and brushed series wound motors by combining the characteristics of both.
• Brushed Permanent Magnet Motor  -  Contain permanent magnets inside, hence the name, which eliminates the need for external field current.  This design yields a smaller, lighter, and energy efficient brush motor.
• Brushed Separately Excited Motor  -  Used for its high torque capability at low speeds which is achieved by separately generating a high stator field current and enough armature voltage to produce the required rotor torque current.
• Brushed Series Wound Motor  -  Speed varies automatically with the load, increasing as the load decreases.
• Brushed Shunt Wound Motor  -  Run at constant speed regardless of the load.

C

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• Cogging  -  Non-uniform or erratic rotation of a direct current motor.  It usually occurs at low speeds and may be a function of the adjustable speed control or of the motor design.
• Commutator  -  A mechanism which reverses the direction of current in certain electric motors.
• Counter Electromotive Force  -  Voltage that opposes line voltage caused by induced magnetic field in a motor armature or rotor.
• Current  -  The current flow is caused by the movement of electrons, which are negatively charged particles, through a conductor such as a wire.  The rate of flow of electric charge (current) is typically determined by the voltage (potential difference) applied across the conductor and the resistance of the conductor.
• Cycles Per Revolution  -  Cycles per revolution are the number of output pulses per complete revolution of the encoder disk.

D

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• Demagnetization (Current)  -  When a permanent magnet DC motor is subjected to high current pulses at which the motor permanent magnets will be demagnetized.  This is an irreversible effect which will alter the motor characteristics and degrade performance.
• Detent Torque  -  The holding torque when no current is flowing in the motor.  The maximum torque which can be applied to the shaft of an unenergized step motor without causing continuous rotation.  The minimal torque present in an unenergized motor.  The detent torque of a step motor is typically about 1% of its static energized torque.
• Direct Current  -  An electrical current that flows in one direction through a conductor.  Unlike alternating current (AC), which periodically reverses direction, DC flows consistently in one direction.
• Duty Cycle  -  The relationship between the operating and rest times or repeatable operation at different loads.
• Dynamic Braking  -  Using a DC motor as a generator, taking it off the supply line and applying an energy dissipating resistor to the armature circuit.  An AC motor's dynamic braking may be done by disconnecting the motor from the line and applying DC to the stator winding.

E

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• Eddy Current  -  Localized currents induced in an iron core by alternating magnetic flux.  These currents translate into losses (heat) and their minimization is an important factor in lamination design.
• End Shield  -  The part of a motor that houses the bearing supporting the rotor and acts as a protective guard to the internal parts of the motor; sometimes called endbell, endplate or end bracket.
• Energy Efficiency  -  A measure used to quantify the energy efficiency of appliances and systems, particularly in the context of energy consumption and conservation.  It provides consumers with a standardized way to compare the energy efficiency of different products and make informed decisions when purchasing appliances.

F

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• Field  -  The stationary part of a DC motor, commonly consisting of permanent magnets.  Sometimes used also to describe the stator of an AC motor.
• Field Weakening  -  The reduction of voltage, and therefore current, to a DC motor shunt field to obtain speeds above the base speed.  The motor horsepower is usually held constant in the field weakened speed range.
• Foot-Pound  -  Energy required to raise a one-pound weight against the force of gravity the distance of one foot.  A measure of torque. Inch pound is also commonly used on smaller motors and gear reducers.  An inch-pound represents the energy needed to lift one pound one inch; an inch-ounce represents the energy needed to lift one ounce one inch.
• Form-Wound Coil  -  A coil made with rectangular or square wire, usually covered with insulation such that it is essentially self-supporting.  It is formed into the required­ shape before insertion into a machine.
• Frequency  -  Alternating electric current frequency is an expression of how often a complete cycle occurs.  Cycles per second describe how many complete cycles occur in a given time increment.  Hertz has been adopted to describe cycles per second so that time as well as number of cycles is specified.  The standard power supply in North America is 60 hz.  Most of the rest of the world has 50 hz power.
• Friction Torque  -  The sum of torque losses independent of motor speed.  These losses include those caused by static mechanical friction of the ball bearings and magnetic hysteresis of the stator.
• Full-Load Current  -  The current required for any electrical machine to produce its rated output or perform its rated function.
• Full-Load Speed  -  The speed at which any rotating machine produces its rated output.
• Full-Load Torque  -  The torque required to produce rated power at full-load speed.
• Fuse  -  A piece of metal, connected in the circuit to be protected, that melts and interrupts the circuit when excess current flows.

G

H

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• Hermetic Motor  -  A motor sealed from the environment and cooled with a refrigerant.
• Holding Torque  -  The maximum torque that can be externally applied to the step motor shaft without causing continuous rotation when one or more phases of the motor are energized.
• Hot Spot  -  The hottest winding spot reached during the rated operation of a machine.

I

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• Impedance  -  The total opposition in an electric circuit to the flow of an alternating current.
• Inrunner  -  A type of brushless DC Motor where their rotational core is contained within the motor's can, typically used in RC automotives and aircrafts.
• Induction Motor  -  The simplest and most rugged electric motor, it consists of a wound stator and a rotor assembly.  The AC induction motor is named because the electric current flowing in its secondary member (the rotor) is induced by the alternating current flowing in its primary member (the stator).  The power supply is connected only to the stator.  The combined electromagnetic effects of the two currents produce the force to create rotation.
• Inrush Current  -  The initial surge of current into the windings.  Inrush current can be up to ten times higher than the continuously needed current because there is low initial resistance.
• Interpole  -  A narrow pole centred on a DC machine's neutral axis, the winding of which is connected in series with the armature circuit and provides a neutralizing effect to aid commutation.
• Inverter  -  A device that converts power from a DC source to AC power at a specified voltage and frequency.  The term inverter is commonly associated with electronic drives that rectify AC line power into DC, then invert the DC into AC power with variable frequency and voltage.

J

K

L

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• Lap Winding  -  A winding in which the coils lay over each other have the same slot pitch and no common center; that is, they are not concentric. In a DC machine armature, the coil ends are connected to adjacent bars (if simplex) of the commutator.
• Leakage Current  -  During dielectric testing, the current flowing through the insulation as a result of the applied test voltage.  In an AC test of insulation, it is the element of the total current that is in phase with the test voltage.  In a DC test of insulation, it is the value of steady-state current after the capacitive and absorptive currents have decayed to negligible values.

M

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• Material Hardness  -  The ability of a material to resist deformation, indentation, or scratching.  It is a measure of how resistant a material is to penetration or permanent indentation.  Hardness is an important property for various materials, especially metals, ceramics, and polymers, as it affects their durability, wear resistance, and suitability for specific applications.
• Maximum Running Torque  -  The maximum torque load that the motor can drive without missing a step.  This typically occurs when the windings are sequentially energized at approximately 5 pps.
• Maximum Torque  -  Can be applied to the shaft of an unenergized step motor without causing continuous rotation.
• Minimal Torque  -  Present in an unenergized motor.
• Motor Efficiency  -  The ratio of useful mechanical power output to the electrical power input in an electric motor.  It measures how effectively an electric motor converts electrical energy into mechanical work or output power.
• Motor Volumetric Efficiency  -  A measure used in the automotive industry to assess how well an internal combustion engine can draw in and expel air during the intake and exhaust strokes, respectively.  It is a factor in determining the engine's overall performance and efficiency.  Volumetric efficiency is expressed as a percentage and represents the ratio of the amount of air an engine draws in or expels compared to its theoretical maximum.

N

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• No-load Speed (rpm)  -  The maximum speed the motor attains with no additional torque load at a given voltage.  This value varies according to the voltage applied to the motor.
• No-load Current (A)  -  The current consumption of the motor at nominal voltage and under no-load conditions.  This value varies proportionally to speed and is influenced by temperature.

O

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• Open Circuit  -  A break in an electrical circuit that prevents normal current flow.
• Output Shaft  -  The shaft of a speed reducer assembly that is connected to the load.  This may also be called the drive shaft or the slow speed shaft.
• Outrunner  -  This type of brushless DC Motor spins its outer shell around its windings, typically used in RC automotives and aircrafts.
• Overhung Load  -  A force applied at right angles to a shaft beyond the shaft’s outermost bearing.  This shaft bending load must be supported by the bearing.

P

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• Phase Voltage  -  The electric potential difference across one phase in a polyphase electrical system.  In a three phase machine, phase voltage equals line voltage for a delta connection and 58 percent of line voltage for a wye connection.
• Progressive Connection  -  A coil to commutator connection in which the leads do not cross over each other at the commutator if the winding is lap.  If the connection is made retrogressive, the armature polarity is reversed.

Q

R

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• Rated Torque  -  The torque producing capacity of a motor at a given speed.  This is the maximum torque the motor can deliver to a load and is usually specified with a torque/speed curve.
• Reactance  -  The opposition to a flow of current other than pure resistance. Inductive reactance is the opposition to change of current in an inductance (coil of wire).  Capacitive reactance is the opposition to change of voltage in a capacitor.
• Rectification  -  The process by which alternating current is converted to direct current by means of a rectifier within an AC Motor.
• Reluctance  -  The characteristics of a magnetic field which resist the flow of magnetic lines of force through it.
• Resistance  -  A measure of how much an object or substance opposes the flow of electric current through it.  In order to overcome the resistance and get the current to flow a higher voltage will be required.
• Rotation  -  The direction in which a shaft turns is either clockwise (CW) or counter clockwise (CCW).  When specifying rotation, also state if viewed from the shaft or opposite shaft end of motor.
• Rotor  -  The rotating component of an induction AC motor. It is typically constructed of a laminated, cylindrical iron core with slots for cast aluminum conductors.  Short circuiting end rings complete the “squirrel cage,” which rotates when the moving magnetic field induces a current in the shorted conductors.

S

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• Salient Pole  -  That type of field pole that projects toward the armature.  Commonly the main poles of a DC machine or the rotating DC field poles of a synchronous machine.
• Salient-Pole Winding  -  An AC winding in which the polarity of the coil groups alternate.
• Secondary Winding  -  The winding of an electric machine that is not connected to the power source but carries current (and voltage) induced in it via its magnetic linkage with the primary winding.
• Self-Locking  -  The inability of a reducer to be driven backwards by its load.
• Servo Drive  -  A motor drive which utilizes internal feedback loops for accurate control of motor current and/or velocity.
• Shaft Currents  -  A circulating current in a rotating machine that can damage bearings.  In an electrical machine, the origin may be dissymmetries in the magnetic paths through the stator/field frame and rotor/armature iron.
• Short Circuit  -  A fault or defect in a winding causing part of the normal electrical circuit to be bypassed, frequently resulting in overheating of the winding and burnout.
• Simplex Winding  -  In a DC machine armature, a simplex is a single winding.  A simplex wave winding has two circuits, and a simplex lap winding has as many circuits as poles.
• Skein Winding  -  A winding with coils produced by a skein of wires.
• Skew  -  The arrangement of laminations in a rotating ­machine core to provide a slight diagonal pattern of the slots with respect to the shaft axis.  This pattern reduces low-speed cogging effects in armatures and induced vibration in rotors.
• Slip  -  The difference between synchronous and operating speeds, compared to synchronous speed, expressed as a percentage. Also, the difference between synchronous and operating speeds is expressed in rpm.
• Space Factor  -  The ratio of the winding space occupied by the bare wire of an insulated conductor to the winding space available. In general, a higher space factor indicates that the winding has lower power losses and higher thermal conductivity.
• Stall Torque  -  Given a particular voltage and frequency, the maximum torque in which the motor can run.  Exceeding this amount will cause the motor to stall.
• Static Friction Torque  -  When a motor is stopped by a brake for example, it is the torque output needed to hold a load as the motor stops.
• Stator  -  The stationary part of a rotating electric machine.  Commonly used to describe the stationary part of an AC machine that contains the primary windings.
• Stepper Drive  -  Electronics which convert step and direction inputs to high power currents and voltages to drive a stepping motor.  The stepping motor driver is analogous to the servo motor amplifier.
• Submersible Motor  -  One so constructed that it will operate successfully when submerged in water under specified conditions of pressure and time.
• Surge Arrester  -  A protective device that passes surge voltage above a certain value harmlessly to the ground and has continuous insulation for normal voltage.
• Synchronous Speed  -  The speed of the rotating magnetic field created by the primary winding of a rotating electric machine.  When the rotating element's speed matches the speed of the magnetic field, it is said to be rotating at synchronous speed.

T

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• Thermocouple  -  A junction of two dissimilar metals that generates a minute voltage in proportion to temperature.  Such devices may be used for temperature detection and thermal protection.
• Torque  -  A type of force that is applied to an object that results in the object rotating around an axis.  It is a measure of how much twisting is applied to an object.
• Transistor - A solid-state three-terminal device that allows amplification of signals and can be used for switching and control.

U

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• Unbalanced Magnetic Pull  -  Radial magnetic pull of the rotor of a rotating electric machine due to unequal magnetic attraction all the way around the periphery of the rotor.  Common causes are shorted or open windings, shorted laminations, and unequal air gap.
• Undercommutation  -  Commutation in which the current changes direction too slowly, evidenced by sparking at the trailing edge of a brush.  It can be caused by interpoles that are too weak magnetically.
• Unifilar Winding  -  The winding configuration of the step motor where each stator pole has one set of windings; the step motor will have only 4 lead wires.  This winding configuration can only be driven from a bipolar driver.

V

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• Variable Frequency Drive  -  A device used to control the speed and rotational output of an alternating current (AC) electric motor by adjusting the frequency and voltage supplied to the motor.  By increasing the frequency, the motor can speed itself up and down as required by the control process.

W

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• Wave Winding  -  A series style winding used mostly for DC machine armatures and AC machine wound rotors.  It often has more than one coil per winding slot. In a DC machine armature, the coil ends are connected to commutator bars that are two pole pitches apart.
• Wet Winding  -  Process by which liquid is applied by brush or other means between the individual layers of insulation at the time of winding.
• Wye Connection  -  A three-phase winding connection formed by joining one end of each phase to make a “Y” point.  The other ends of each phase are connected to the line. Also termed a star connection.
• Wye-delta Starting  -  Wye-delta is a connection used to reduce the inrush current and torque of a three-phase motor.  A wye (star) start, delta run motor is arranged to start by connecting to the line with the winding initially connected wye (star). The winding is then reconnected to run in delta after a predetermined time.  The lead numbers for a single run voltage are normally 1,2,3,4,5, and 6.

X

Y

• Yield Strength  -  The minimum stress that leads to permanent deformation of the material.   It is important to note that the yield strength of a material is not a fixed value, but rather depends on various factors such as the composition, processing, and testing conditions of the material.

Z