Electric_motor

context: Found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives, electric motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or rectifiers, or by alternating current (AC) sources, such as from the power grid, inverters or generators. Small motors may be found in electric watches. General-purpose motors with highly standardized dimensions and characteristics provide convenient mechanical power for industrial use. The largest of electric motors are used for ship propulsion, pipeline compression and pumped-storage applications with ratings reaching 100 megawatts. Electric motors may be classified by electric power source type, internal construction, application, type of motion output, and so on.
qas: answers: text: 100 megawatts
question: What is the largest rating of an electric motor?

answers: text: batteries
question: What is the main example of a DC power source?

answers: text: alternating current
question: What does AC stand for?

answers: text: direct current
question: What does DC stand for?

answers: text: electric watches
question: In what device are small motors commonly found?

context: Perhaps the first electric motors were simple electrostatic devices created by the Scottish monk Andrew Gordon in the 1740s. The theoretical principle behind production of mechanical force by the interactions of an electric current and a magnetic field, Ampère's force law, was discovered later by André-Marie Ampère in 1820. The conversion of electrical energy into mechanical energy by electromagnetic means was demonstrated by the British scientist Michael Faraday in 1821. A free-hanging wire was dipped into a pool of mercury, on which a permanent magnet (PM) was placed. When a current was passed through the wire, the wire rotated around the magnet, showing that the current gave rise to a close circular magnetic field around the wire. This motor is often demonstrated in physics experiments, brine substituting for toxic mercury. Though Barlow's wheel was an early refinement to this Faraday demonstration, these and similar homopolar motors were to remain unsuited to practical application until late in the century.
qas: answers: text: Andrew Gordon
question: Who created the first electrostatic device?

answers: text: André-Marie Ampère
question: Who discovered the principles of magnetic and electric interactions?

answers: text: 1821
question: In what year did Faraday convert electrical energy into mechanical energy?

answers: text: mercury
question: What toxic substance originally served the function of brine in primitive motors?

context: In 1827, Hungarian physicist Ányos Jedlik started experimenting with electromagnetic coils. After Jedlik solved the technical problems of the continuous rotation with the invention of the commutator, he called his early devices "electromagnetic self-rotors". Although they were used only for instructional purposes, in 1828 Jedlik demonstrated the first device to contain the three main components of practical DC motors: the stator, rotor and commutator. The device employed no permanent magnets, as the magnetic fields of both the stationary and revolving components were produced solely by the currents flowing through their windings.
qas: answers: text: 1827
question: In what year did Jedlik begin experimenting with electromagnetism?

answers: text: rotor
question: Besides the stator and the communicator, what is an element of a DC motor?

answers: text: electromagnetic self-rotors
question: What did Jedlik call his earliest devices?

answers: text: commutator
question: What discovery solved the problem of continuous rotation?

answers: text: permanent magnets
question: What did Jedlik's improved device eliminate the need for?

context: After many other more or less successful attempts with relatively weak rotating and reciprocating apparatus the Prussian Moritz von Jacobi created the first real rotating electric motor in May 1834 that actually developed a remarkable mechanical output power. His motor set a world record which was improved only four years later in September 1838 by Jacobi himself. His second motor was powerful enough to drive a boat with 14 people across a wide river. It was not until 1839/40 that other developers worldwide managed to build motors of similar and later also of higher performance.
qas: answers: text: 1839/40
question: When were developers competing with Jacobi able to match his accomplishments?

answers: text: boat
question: What was Jacobi's improved motor used to propel?

answers: text: Moritz von Jacobi
question: Who created the first real electric motor?

answers: text: Jacobi himself
question: Who broke the world record set by Jacobi's first motor?

answers: text: four years
question: How long did it take for Jacobi's first world record to be broken?

context: The first commutator DC electric motor capable of turning machinery was invented by the British scientist William Sturgeon in 1832. Following Sturgeon's work, a commutator-type direct-current electric motor made with the intention of commercial use was built by the American inventor Thomas Davenport, which he patented in 1837. The motors ran at up to 600 revolutions per minute, and powered machine tools and a printing press. Due to the high cost of primary battery power, the motors were commercially unsuccessful and Davenport went bankrupt. Several inventors followed Sturgeon in the development of DC motors but all encountered the same battery power cost issues. No electricity distribution had been developed at the time. Like Sturgeon's motor, there was no practical commercial market for these motors.
qas: answers: text: William Sturgeon
question: Who developed the first mnotor capable of being used for machinery?

answers: text: Thomas Davenport
question: Which inventor went bankrupt?

answers: text: the high cost of primary battery power
question: What was the main problem with applying early electric motors to industry?

answers: text: electricity distribution
question: What necessary technical development had yet to occur to make electric motors useful?

answers: text: 600 revolutions per minute
question: How fast did Sturgeon and Davenport's motors run?

context: A major turning point in the development of DC machines took place in 1864, when Antonio Pacinotti described for the first time the ring armature with its symmetrically grouped coils closed upon themselves and connected to the bars of a commutator, the brushes of which delivered practically non-fluctuating current. The first commercially successful DC motors followed the invention by Zénobe Gramme who, in 1871, reinvented Pacinotti's design. In 1873, Gramme showed that his dynamo could be used as a motor, which he demonstrated to great effect at exhibitions in Vienna and Philadelphia by connecting two such DC motors at a distance of up to 2 km away from each other, one as a generator. (See also 1873 : l'expérience décisive [Decisive Workaround] .)
qas: answers: text: non-fluctuating current
question: What made Pacinotti's motor an important advancement?

answers: text: Zénobe Gramme
question: Who created a motor similar to Pacinotti?

answers: text: 2 km
question: How far from each other were the motors in Gramme's demonstrations?

answers: text: generator
question: Besides a motor, what did Gramme use the other device for?

answers: text: Vienna and Philadelphia
question: In what two cities did Gramme conduct his demonstrations?

context: In 1886, Frank Julian Sprague invented the first practical DC motor, a non-sparking motor that maintained relatively constant speed under variable loads. Other Sprague electric inventions about this time greatly improved grid electric distribution (prior work done while employed by Thomas Edison), allowed power from electric motors to be returned to the electric grid, provided for electric distribution to trolleys via overhead wires and the trolley pole, and provided controls systems for electric operations. This allowed Sprague to use electric motors to invent the first electric trolley system in 1887–88 in Richmond VA, the electric elevator and control system in 1892, and the electric subway with independently powered centrally controlled cars, which were first installed in 1892 in Chicago by the South Side Elevated Railway where it became popularly known as the "L". Sprague's motor and related inventions led to an explosion of interest and use in electric motors for industry, while almost simultaneously another great inventor was developing its primary competitor, which would become much more widespread. The development of electric motors of acceptable efficiency was delayed for several decades by failure to recognize the extreme importance of a relatively small air gap between rotor and stator. Efficient designs have a comparatively small air gap. [a] The St. Louis motor, long used in classrooms to illustrate motor principles, is extremely inefficient for the same reason, as well as appearing nothing like a modern motor.
qas: answers: text: small air gap
question: What needs to exist between the rotor and stator for increased efficiency?

answers: text: Frank Julian Sprague
question: Which inventor created the first useful DC motor?

answers: text: electric trolley system
question: What was the transportation advancement made possible by Sprague's designs?

answers: text: South Side Elevated Railway
question: What was the name of Chicago's first electric trolley system?

answers: text: Thomas Edison
question: Who did Sprague work for early in his career?

context: Application of electric motors revolutionized industry. Industrial processes were no longer limited by power transmission using line shafts, belts, compressed air or hydraulic pressure. Instead every machine could be equipped with its own electric motor, providing easy control at the point of use, and improving power transmission efficiency. Electric motors applied in agriculture eliminated human and animal muscle power from such tasks as handling grain or pumping water. Household uses of electric motors reduced heavy labor in the home and made higher standards of convenience, comfort and safety possible. Today, electric motors stand for more than half of the electric energy consumption in the US.
qas: answers: text: more than half
question: How much energy do electric motors use in the modern United States?

answers: text: agriculture
question: In what domain did electric motors reduce reliance on humans and animals?

answers: text: hydraulic pressure
question: Besides shafts, belts and compressed air, what did electric motors reduce the need for?

answers: text: in the home
question: Where did electric motors improve convenience and safety?

context: In 1824, the French physicist François Arago formulated the existence of rotating magnetic fields, termed Arago's rotations, which, by manually turning switches on and off, Walter Baily demonstrated in 1879 as in effect the first primitive induction motor.  In the 1880s, many inventors were trying to develop workable AC motors because AC's advantages in long-distance high-voltage transmission were counterbalanced by the inability to operate motors on AC. The first alternating-current commutatorless induction motors were independently invented by Galileo Ferraris and Nikola Tesla, a working motor model having been demonstrated by the former in 1885 and by the latter in 1887. In 1888, the Royal Academy of Science of Turin published Ferraris' research detailing the foundations of motor operation while however concluding that "the apparatus based on that principle could not be of any commercial importance as motor." In 1888, Tesla presented his paper A New System for Alternating Current Motors and Transformers to the AIEE that described three patented two-phase four-stator-pole motor types: one with a four-pole rotor forming a non-self-starting reluctance motor, another with a wound rotor forming a self-starting induction motor, and the third a true synchronous motor with separately excited DC supply to rotor winding. One of the patents Tesla filed in 1887, however, also described a shorted-winding-rotor induction motor. George Westinghouse promptly bought Tesla's patents, employed Tesla to develop them, and assigned C. F. Scott to help Tesla, Tesla left for other pursuits in 1889.  The constant speed AC induction motor was found not to be suitable for street cars but Westinghouse engineers successfully adapted it to power a mining operation in Telluride, Colorado in 1891. Steadfast in his promotion of three-phase development, Mikhail Dolivo-Dobrovolsky invented the three-phase cage-rotor induction motor in 1889 and the three-limb transformer in 1890. This type of motor is now used for the vast majority of commercial applications. However, he claimed that Tesla's motor was not practical because of two-phase pulsations, which prompted him to persist in his three-phase work. Although Westinghouse achieved its first practical induction motor in 1892 and developed a line of polyphase 60 hertz induction motors in 1893, these early Westinghouse motors were two-phase motors with wound rotors until B. G. Lamme developed a rotating bar winding rotor. The General Electric Company began developing three-phase induction motors in 1891. By 1896, General Electric and Westinghouse signed a cross-licensing agreement for the bar-winding-rotor design, later called the squirrel-cage rotor. Induction motor improvements flowing from these inventions and innovations were such that a 100 horsepower (HP) induction motor currently has the same mounting dimensions as a 7.5 HP motor in 1897.
qas: answers: text: Walter Baily
question: Who built the first induction motor?

answers: text: AC
question: What type of power were early motors unable to use?

answers: text: George Westinghouse
question: Who bought Tesla's patents?

answers: text: mining
question: For what application was Tesla's motor first used?

answers: text: squirrel-cage
question: What's another name for the bar-winding-rotor?

context: A commutator is a mechanism used to switch the input of most DC machines and certain AC machines consisting of slip ring segments insulated from each other and from the electric motor's shaft. The motor's armature current is supplied through the stationary brushes in contact with the revolving commutator, which causes required current reversal and applies power to the machine in an optimal manner as the rotor rotates from pole to pole. In absence of such current reversal, the motor would brake to a stop. In light of significant advances in the past few decades due to improved technologies in electronic controller, sensorless control, induction motor, and permanent magnet motor fields, electromechanically commutated motors are increasingly being displaced by externally commutated induction and permanent-magnet motors.
qas: answers: text: brake to a stop
question: What would a rotor do without current reversal?

answers: text: commutator
question: What switches the input of most DC motors?

answers: text: stationary brushes
question: From where is current to the motor supplied?

answers: text: externally commutated induction and permanent-magnet
question: What two motor types are ascendant today?

context: A commutated DC motor has a set of rotating windings wound on an armature mounted on a rotating shaft. The shaft also carries the commutator, a long-lasting rotary electrical switch that periodically reverses the flow of current in the rotor windings as the shaft rotates. Thus, every brushed DC motor has AC flowing through its rotating windings. Current flows through one or more pairs of brushes that bear on the commutator; the brushes connect an external source of electric power to the rotating armature.
qas: answers: text: reverses the flow of current in the rotor windings
question: What does the communicator do?

answers: text: AC
question: What type of current is featured in brushed DC motors?

answers: text: external
question: Where do brushes get their power?

answers: text: rotating
question: What is the main feature of the shaft in a commutated DC motor?

context: The rotating armature consists of one or more coils of wire wound around a laminated, magnetically "soft" ferromagnetic core. Current from the brushes flows through the commutator and one winding of the armature, making it a temporary magnet (an electromagnet). The magnetic field produced by the armature interacts with a stationary magnetic field produced by either PMs or another winding a field coil, as part of the motor frame. The force between the two magnetic fields tends to rotate the motor shaft. The commutator switches power to the coils as the rotor turns, keeping the magnetic poles of the rotor from ever fully aligning with the magnetic poles of the stator field, so that the rotor never stops (like a compass needle does), but rather keeps rotating as long as power is applied.
qas: answers: text: electromagnet
question: Current flowing to create a temporary magent is called what?

answers: text: force between the two magnetic fields
question: What rotates the motor shaft?

answers: text: commutator
question: What element of the motor keeps the poles from alligning?

answers: text: compass
question: What non-motor device demonstrates why a commutator is needed?

context: Many of the limitations of the classic commutator DC motor are due to the need for brushes to press against the commutator. This creates friction. Sparks are created by the brushes making and breaking circuits through the rotor coils as the brushes cross the insulating gaps between commutator sections. Depending on the commutator design, this may include the brushes shorting together adjacent sections – and hence coil ends – momentarily while crossing the gaps. Furthermore, the inductance of the rotor coils causes the voltage across each to rise when its circuit is opened, increasing the sparking of the brushes. This sparking limits the maximum speed of the machine, as too-rapid sparking will overheat, erode, or even melt the commutator. The current density per unit area of the brushes, in combination with their resistivity, limits the output of the motor. The making and breaking of electric contact also generates electrical noise; sparking generates RFI. Brushes eventually wear out and require replacement, and the commutator itself is subject to wear and maintenance (on larger motors) or replacement (on small motors). The commutator assembly on a large motor is a costly element, requiring precision assembly of many parts. On small motors, the commutator is usually permanently integrated into the rotor, so replacing it usually requires replacing the whole rotor.
qas: answers: text: sparking
question: How is RFI generated?

answers: text: commutator
question: What do brushes need to be in contact with?

answers: text: friction
question: What is created by contact between parts of the motor?

answers: text: maximum speed
question: What does sparking limit?

answers: text: Brushes
question: What motor components most need replacement and maintenance? 

context: Large brushes are desired for a larger brush contact area to maximize motor output, but small brushes are desired for low mass to maximize the speed at which the motor can run without the brushes excessively bouncing and sparking. (Small brushes are also desirable for lower cost.) Stiffer brush springs can also be used to make brushes of a given mass work at a higher speed, but at the cost of greater friction losses (lower efficiency) and accelerated brush and commutator wear. Therefore, DC motor brush design entails a trade-off between output power, speed, and efficiency/wear.
qas: answers: text: motor output
question: What are large brushes favorable for?

answers: text: speed
question: Whate are small brushes favorable for?

answers: text: small
question: What type of brushes are cheapest?

answers: text: Stiffer brush springs
question: How can the speed of larger brushes be increased?

answers: text: lower efficiency
question: Besides wear, what is a downside of stiff brush springs?

context: A PM motor does not have a field winding on the stator frame, instead relying on PMs to provide the magnetic field against which the rotor field interacts to produce torque. Compensating windings in series with the armature may be used on large motors to improve commutation under load. Because this field is fixed, it cannot be adjusted for speed control. PM fields (stators) are convenient in miniature motors to eliminate the power consumption of the field winding. Most larger DC motors are of the "dynamo" type, which have stator windings. Historically, PMs could not be made to retain high flux if they were disassembled; field windings were more practical to obtain the needed amount of flux. However, large PMs are costly, as well as dangerous and difficult to assemble; this favors wound fields for large machines.
qas: answers: text: speed control
question: What can a PM motor not be adjusted for?

answers: text: stators
question: What is another name for PM fields?

answers: text: field winding
question: What design feature does a PM motor lack?

answers: text: flux
question: What do field windings provide?

context: To minimize overall weight and size, miniature PM motors may use high energy magnets made with neodymium or other strategic elements; most such are neodymium-iron-boron alloy. With their higher flux density, electric machines with high-energy PMs are at least competitive with all optimally designed singly-fed synchronous and induction electric machines. Miniature motors resemble the structure in the illustration, except that they have at least three rotor poles (to ensure starting, regardless of rotor position) and their outer housing is a steel tube that magnetically links the exteriors of the curved field magnets.
qas: answers: text: To minimize overall weight and size
question: Why do miniature PM motors use high energy magnets?

answers: text: neodymium-iron-boron alloy
question: What are high energy magnets typically made of?

answers: text: steel tube
question: What does the outer housing of a miniature motor resemble?

answers: text: least competitive
question: How do PMs rate against other types of electric motors?

context: Operating at normal power line frequencies, universal motors are often found in a range less than 1000 watts. Universal motors also formed the basis of the traditional railway traction motor in electric railways. In this application, the use of AC to power a motor originally designed to run on DC would lead to efficiency losses due to eddy current heating of their magnetic components, particularly the motor field pole-pieces that, for DC, would have used solid (un-laminated) iron and they are now rarely used.
qas: answers: text: 1000 watts
question: What is the typical maximum range of universal motors?

answers: text: universal
question: What type of motor was used in trailway traction applications?

answers: text: efficiency losses
question: What is the result of using AC power on a DC motor?

answers: text: solid (un-laminated) iron
question: What were universal motor pole pieces constructed from?

context: An advantage of the universal motor is that AC supplies may be used on motors which have some characteristics more common in DC motors, specifically high starting torque and very compact design if high running speeds are used. The negative aspect is the maintenance and short life problems caused by the commutator. Such motors are used in devices such as food mixers and power tools which are used only intermittently, and often have high starting-torque demands. Multiple taps on the field coil provide (imprecise) stepped speed control. Household blenders that advertise many speeds frequently combine a field coil with several taps and a diode that can be inserted in series with the motor (causing the motor to run on half-wave rectified AC). Universal motors also lend themselves to electronic speed control and, as such, are an ideal choice for devices like domestic washing machines. The motor can be used to agitate the drum (both forwards and in reverse) by switching the field winding with respect to the armature.
qas: answers: text: universal
question: What kind of motor can employ both AC and DC?

answers: text: commutator
question: What component of a universal motor is most likely to fail?

answers: text: starting
question: When is torque most important in universal motor applications?

answers: text: forwards and in reverse
question: Switching the field winding in washing machines causes the drum to agitate how?

answers: text: Multiple taps on the field coil provide
question: How is stepped speed control achieved?

context: Whereas SCIMs cannot turn a shaft faster than allowed by the power line frequency, universal motors can run at much higher speeds. This makes them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high speed and light weight are desirable. They are also commonly used in portable power tools, such as drills, sanders, circular and jig saws, where the motor's characteristics work well. Many vacuum cleaner and weed trimmer motors exceed 10,000 rpm, while many similar miniature grinders exceed 30,000 rpm.
qas: answers: text: 10,000
question: At around what RMP do weed trimmer motors operate?

answers: text: 30,000
question: At around what RMP do miniature grinders operate?

answers: text: SCIMs
question: What type of motor can universal motors operate much faster than?

answers: text: high speed and light weight
question: What attributes make universal motors desireable for consumer applications like hair dryers?

context: Currents induced into this winding provide the rotor magnetic field. The shape of the rotor bars determines the speed-torque characteristics. At low speeds, the current induced in the squirrel cage is nearly at line frequency and tends to be in the outer parts of the rotor cage. As the motor accelerates, the slip frequency becomes lower, and more current is in the interior of the winding. By shaping the bars to change the resistance of the winding portions in the interior and outer parts of the cage, effectively a variable resistance is inserted in the rotor circuit. However, the majority of such motors have uniform bars.
qas: answers: text: shape of the rotor bars
question: What determines the properties of speed and torque?

answers: text: interior of the winding
question: At high speed, where is the most current?

answers: text: lower
question: Is the current frequency higher or lower at high speed?

answers: text: variable resistance
question: Changing the shapes of the bars creates what?

answers: text: rotor circuit
question: Where can variable resistance be created?

context: In a WRIM, the rotor winding is made of many turns of insulated wire and is connected to slip rings on the motor shaft. An external resistor or other control devices can be connected in the rotor circuit. Resistors allow control of the motor speed, although significant power is dissipated in the external resistance. A converter can be fed from the rotor circuit and return the slip-frequency power that would otherwise be wasted back into the power system through an inverter or separate motor-generator.
qas: answers: text: rotor circuit
question: Where might a resistor be attached?

answers: text: motor speed
question: What can a resistor control?

answers: text: inverter or separate motor-generator
question: How might wasted power be salvaged?

answers: text: rotor circuit
question: From where may a converter be fed?

context: When used with a load that has a torque curve that increases with speed, the motor will operate at the speed where the torque developed by the motor is equal to the load torque. Reducing the load will cause the motor to speed up, and increasing the load will cause the motor to slow down until the load and motor torque are equal. Operated in this manner, the slip losses are dissipated in the secondary resistors and can be very significant. The speed regulation and net efficiency is also very poor.
qas: answers: text: speed up
question: What will a motor do if the load is reduced?

answers: text: slow down
question: What will a motor do if the load is increased?

answers: text: secondary resistors
question: Where are slip losses dissipated?

answers: text: very poor
question: How efficient is such a design?

context: A common application of a torque motor would be the supply- and take-up reel motors in a tape drive. In this application, driven from a low voltage, the characteristics of these motors allow a relatively constant light tension to be applied to the tape whether or not the capstan is feeding tape past the tape heads. Driven from a higher voltage, (and so delivering a higher torque), the torque motors can also achieve fast-forward and rewind operation without requiring any additional mechanics such as gears or clutches. In the computer gaming world, torque motors are used in force feedback steering wheels.
qas: answers: text: feedback steering wheels
question: How are torque motors used in computer gaming?

answers: text: constant light tension
question: A torque motor at low voltage provides what?

answers: text: higher torque
question: A torque motor at high voltage provides what?

answers: text: gears or clutches
question: In a tape drive, what is not needed if a torque motor is used?

context: Another common application is the control of the throttle of an internal combustion engine in conjunction with an electronic governor. In this usage, the motor works against a return spring to move the throttle in accordance with the output of the governor. The latter monitors engine speed by counting electrical pulses from the ignition system or from a magnetic pickup and, depending on the speed, makes small adjustments to the amount of current applied to the motor. If the engine starts to slow down relative to the desired speed, the current will be increased, the motor will develop more torque, pulling against the return spring and opening the throttle. Should the engine run too fast, the governor will reduce the current being applied to the motor, causing the return spring to pull back and close the throttle.
qas: answers: text: electrical pulses
question: What element of a combustion engine does a governor monitor?

answers: text: return spring
question: What is a governor connected to?

answers: text: small
question: What kinds of adjustments would a governor make?

answers: text: reduce the current being applied to the motor
question: What would a governor do to a too-fast running engine?

context: A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the AC and resulting magnetic field which drives it. Another way of saying this is that it has zero slip under usual operating conditions. Contrast this with an induction motor, which must slip to produce torque. One type of synchronous motor is like an induction motor except the rotor is excited by a DC field. Slip rings and brushes are used to conduct current to the rotor. The rotor poles connect to each other and move at the same speed hence the name synchronous motor. Another type, for low load torque, has flats ground onto a conventional squirrel-cage rotor to create discrete poles. Yet another, such as made by Hammond for its pre-World War II clocks, and in the older Hammond organs, has no rotor windings and discrete poles. It is not self-starting. The clock requires manual starting by a small knob on the back, while the older Hammond organs had an auxiliary starting motor connected by a spring-loaded manually operated switch.
qas: answers: text: zero
question: How much slip does a synchronous motor have?

answers: text: slip
question: How does an induction motor produce torque?

answers: text: manually
question: Whithout rotor windings, how must a Hammond clock be started?

answers: text: DC field
question: How can a synchronous motor be made more like an induction motor?

answers: text: Slip rings and brushes
question: How is current brought to the rotor in a synchronous motor?

context: Finally, hysteresis synchronous motors typically are (essentially) two-phase motors with a phase-shifting capacitor for one phase. They start like induction motors, but when slip rate decreases sufficiently, the rotor (a smooth cylinder) becomes temporarily magnetized. Its distributed poles make it act like a PMSM. The rotor material, like that of a common nail, will stay magnetized, but can also be demagnetized with little difficulty. Once running, the rotor poles stay in place; they do not drift.
qas: answers: text: becomes temporarily magnetized
question: What do hysteresis synchronous motors' rotors do when slip rate decreases?

answers: text: stay in place
question: When in operation, what do hysteresis synchronous motors poles do?

answers: text: induction motors
question: What do hysteresis synchronous motors resemble at startup?

answers: text: a smooth cylinder
question: How can a hysteresis synchronous motor's rotor be described?

answers: text: PMSM
question: What do the distributed poles of a hysteresis synchronous motor resemble?

context: Doubly fed electric motors have two independent multiphase winding sets, which contribute active (i.e., working) power to the energy conversion process, with at least one of the winding sets electronically controlled for variable speed operation. Two independent multiphase winding sets (i.e., dual armature) are the maximum provided in a single package without topology duplication. Doubly-fed electric motors are machines with an effective constant torque speed range that is twice synchronous speed for a given frequency of excitation. This is twice the constant torque speed range as singly-fed electric machines, which have only one active winding set.
qas: answers: text: Doubly fed electric motors
question: What type of motor has two independent multiphase winding sets?

answers: text: contribute active (i.e., working) power to the energy conversion process
question: What advanage do independent multiphase winding sets have?

answers: text: variable speed operation
question: What is one of the independent multiphase winding sets configured for?

answers: text: twice the constant torque speed range
question: Doubly fed motors have what advantage over single fed?

context: Nothing in the principle of any of the motors described above requires that the iron (steel) portions of the rotor actually rotate. If the soft magnetic material of the rotor is made in the form of a cylinder, then (except for the effect of hysteresis) torque is exerted only on the windings of the electromagnets. Taking advantage of this fact is the coreless or ironless DC motor, a specialized form of a PM DC motor. Optimized for rapid acceleration, these motors have a rotor that is constructed without any iron core. The rotor can take the form of a winding-filled cylinder, or a self-supporting structure comprising only the magnet wire and the bonding material. The rotor can fit inside the stator magnets; a magnetically soft stationary cylinder inside the rotor provides a return path for the stator magnetic flux. A second arrangement has the rotor winding basket surrounding the stator magnets. In that design, the rotor fits inside a magnetically soft cylinder that can serve as the housing for the motor, and likewise provides a return path for the flux.
qas: answers: text: rapid acceleration
question: A coreless DC motor is distinguished by what?

answers: text: iron core
question: What is absent in a coreless DC motor?

answers: text: winding-filled cylinder, or a self-supporting structure
question: What forms can the rotor take?

context: Because the rotor is much lighter in weight (mass) than a conventional rotor formed from copper windings on steel laminations, the rotor can accelerate much more rapidly, often achieving a mechanical time constant under one ms. This is especially true if the windings use aluminum rather than the heavier copper. But because there is no metal mass in the rotor to act as a heat sink, even small coreless motors must often be cooled by forced air. Overheating might be an issue for coreless DC motor designs.
qas: answers: text: Overheating
question: What is a likely problem of coreless DC motors?

answers: text: lighter
question: How does a coreless rotor compare to traditional rotors in terms of weight?

answers: text: accelerate much more rapidly
question: What advantage does a coreless rotor have over traditional variants?

answers: text: heat sink
question: The lack of a metal mass in the core causes what function to be absent?

answers: text: forced air
question: How is a coreless motor cooled?

context: These motors were originally invented to drive the capstan(s) of magnetic tape drives in the burgeoning computer industry, where minimal time to reach operating speed and minimal stopping distance were critical. Pancake motors are still widely used in high-performance servo-controlled systems, robotic systems, industrial automation and medical devices. Due to the variety of constructions now available, the technology is used in applications from high temperature military to low cost pump and basic servos.
qas: answers: text: drive the capstan(s) of magnetic tape drives
question: What was the original purpose for pancake motors?

answers: text: minimal time to reach operating speed and minimal stopping distance
question: What are advantages of pancake motors?

answers: text: high temperature
question: For what type of military applications are pancake motors currently used?

answers: text: high-performance
question: What type of servo-controlled systems use pancake motors?

context: A servomotor is a motor, very often sold as a complete module, which is used within a position-control or speed-control feedback control system mainly control valves, such as motor-operated control valves. Servomotors are used in applications such as machine tools, pen plotters, and other process systems. Motors intended for use in a servomechanism must have well-documented characteristics for speed, torque, and power. The speed vs. torque curve is quite important and is high ratio for a servo motor. Dynamic response characteristics such as winding inductance and rotor inertia are also important; these factors limit the overall performance of the servomechanism loop. Large, powerful, but slow-responding servo loops may use conventional AC or DC motors and drive systems with position or speed feedback on the motor. As dynamic response requirements increase, more specialized motor designs such as coreless motors are used. AC motors' superior power density and acceleration characteristics compared to that of DC motors tends to favor PM synchronous, BLDC, induction, and SRM drive applications.
qas: answers: text: machine tools, pen plotters, and other process systems
question: What may servo motors be used for?

answers: text: speed, torque, and power
question: What must be well understood when applying a servo motor for use?

answers: text: winding inductance and rotor inertia
question: What factors limit performance of servo motors?

answers: text: conventional AC or DC motors
question: Large, slow servos can use what types of motors?

answers: text: As dynamic response requirements increase
question: When might coreless motors be used in servo applications?

context: A servo system differs from some stepper motor applications in that the position feedback is continuous while the motor is running; a stepper system relies on the motor not to "miss steps" for short term accuracy, although a stepper system may include a "home" switch or other element to provide long-term stability of control. For instance, when a typical dot matrix computer printer starts up, its controller makes the print head stepper motor drive to its left-hand limit, where a position sensor defines home position and stops stepping. As long as power is on, a bidirectional counter in the printer's microprocessor keeps track of print-head position.
qas: answers: text: position feedback is continuous
question: How do servo motors differ from stepper motors?

answers: text: a "home" switch
question: How does a stepper system achieve stability?

answers: text: position sensor
question: What makes a printer home switch work?

answers: text: bidirectional
question: What kind of counter keeps track of a print head's position?

answers: text: miss steps
question: A stepper system's motor is relied on to not do what?

context: Stepper motors are a type of motor frequently used when precise rotations are required. In a stepper motor an internal rotor containing PMs or a magnetically soft rotor with salient poles is controlled by a set of external magnets that are switched electronically. A stepper motor may also be thought of as a cross between a DC electric motor and a rotary solenoid. As each coil is energized in turn, the rotor aligns itself with the magnetic field produced by the energized field winding. Unlike a synchronous motor, in its application, the stepper motor may not rotate continuously; instead, it "steps"—starts and then quickly stops again—from one position to the next as field windings are energized and de-energized in sequence. Depending on the sequence, the rotor may turn forwards or backwards, and it may change direction, stop, speed up or slow down arbitrarily at any time.
qas: answers: text: when precise rotations are required
question: When are stepper motors most useful?

answers: text: DC electric motor and a rotary solenoid
question: What two devices can describe a stepper motor?

answers: text: magnetic field produced by the energized field winding
question: What do stepper motor rotors allign themselves with?

answers: text: the stepper motor may not rotate continuously
question: How does a stepper motor differ from a synchronous motor?

answers: text: forwards or backwards, and it may change direction, stop, speed up or slow down
question: What types of velocities and positions is the stepper motor capable of?

context: Simple stepper motor drivers entirely energize or entirely de-energize the field windings, leading the rotor to "cog" to a limited number of positions; more sophisticated drivers can proportionally control the power to the field windings, allowing the rotors to position between the cog points and thereby rotate extremely smoothly. This mode of operation is often called microstepping. Computer controlled stepper motors are one of the most versatile forms of positioning systems, particularly when part of a digital servo-controlled system.
qas: answers: text: proportionally control the power to the field windings
question: What is a trait of a sophisticated stepper motor?

answers: text: rotate extremely smoothly
question: What does proportinal control of the field windings in a stepper motor achieve?

answers: text: microstepping
question: What is another name for smooth rotation?

answers: text: digital servo-controlled system
question: With what other device are stepper motors most versatile?

context: Stepper motors can be rotated to a specific angle in discrete steps with ease, and hence stepper motors are used for read/write head positioning in computer floppy diskette drives. They were used for the same purpose in pre-gigabyte era computer disk drives, where the precision and speed they offered was adequate for the correct positioning of the read/write head of a hard disk drive. As drive density increased, the precision and speed limitations of stepper motors made them obsolete for hard drives—the precision limitation made them unusable, and the speed limitation made them uncompetitive—thus newer hard disk drives use voice coil-based head actuator systems. (The term "voice coil" in this connection is historic; it refers to the structure in a typical (cone type) loudspeaker. This structure was used for a while to position the heads. Modern drives have a pivoted coil mount; the coil swings back and forth, something like a blade of a rotating fan. Nevertheless, like a voice coil, modern actuator coil conductors (the magnet wire) move perpendicular to the magnetic lines of force.)
qas: answers: text: precision and speed limitations
question: Why were stepper motors abandoned in computer drive designs?

answers: text: voice coil-based head actuator systems
question: What do newer computer drives use instead of stepper motors?

answers: text: perpendicular to the magnetic lines of force
question: In what direction do modern coil actuators move?

answers: text: the structure in a typical (cone type) loudspeaker
question: To what device does the term, "voice coil" historically refer?

context: Stepper motors were and still are often used in computer printers, optical scanners, and digital photocopiers to move the optical scanning element, the print head carriage (of dot matrix and inkjet printers), and the platen or feed rollers. Likewise, many computer plotters (which since the early 1990s have been replaced with large-format inkjet and laser printers) used rotary stepper motors for pen and platen movement; the typical alternatives here were either linear stepper motors or servomotors with closed-loop analog control systems.
qas: answers: text: linear stepper motors or servomotors
question: List two alternatives to rotary stepper motors in printer applications.

answers: text: optical scanning element
question: In scanners, what do stepper motors move?

answers: text: print head carriage (of dot matrix and inkjet printers), and the platen or feed rollers
question: In printers and copiers, what do stepper motors move?

context: Since the armature windings of a direct-current or universal motor are moving through a magnetic field, they have a voltage induced in them. This voltage tends to oppose the motor supply voltage and so is called "back electromotive force (emf)". The voltage is proportional to the running speed of the motor. The back emf of the motor, plus the voltage drop across the winding internal resistance and brushes, must equal the voltage at the brushes. This provides the fundamental mechanism of speed regulation in a DC motor. If the mechanical load increases, the motor slows down; a lower back emf results, and more current is drawn from the supply. This increased current provides the additional torque to balance the new load.
qas: answers: text: back electromotive force
question: Voltage opposing the motor supply voltage is called what?

answers: text: the running speed of the motor
question: EMP is proportional to what?

answers: text: back emf of the motor, plus the voltage drop across the winding internal resistance
question: Voltage at the brushes is equal to what?

answers: text: more current is drawn from the supply
question: If load increases, what happens to current drawn?

context: All the electromagnetic motors, and that includes the types mentioned here derive the torque from the vector product of the interacting fields. For calculating the torque it is necessary to know the fields in the air gap . Once these have been established by mathematical analysis using FEA or other tools the torque may be calculated as the integral of all the vectors of force multiplied by the radius of each vector. The current flowing in the winding is producing the fields and for a motor using a magnetic material the field is not linearly proportional to the current. This makes the calculation difficult but a computer can do the many calculations needed.
qas: answers: text: fields in the air gap
question: What needs to be known to calculate torque?

answers: text: FEA
question: How are the many calculations to determine torque done?

answers: text: from the vector product of the interacting fields
question: How is torque determined?

answers: text: the integral of all the vectors of force multiplied by the radius of each vector
question: What is the formulia to determine torque?

context: When optimally designed within a given core saturation constraint and for a given active current (i.e., torque current), voltage, pole-pair number, excitation frequency (i.e., synchronous speed), and air-gap flux density, all categories of electric motors or generators will exhibit virtually the same maximum continuous shaft torque (i.e., operating torque) within a given air-gap area with winding slots and back-iron depth, which determines the physical size of electromagnetic core. Some applications require bursts of torque beyond the maximum operating torque, such as short bursts of torque to accelerate an electric vehicle from standstill. Always limited by magnetic core saturation or safe operating temperature rise and voltage, the capacity for torque bursts beyond the maximum operating torque differs significantly between categories of electric motors or generators.
qas: answers: text: torque current), voltage, pole-pair number, excitation frequency (i.e., synchronous speed), and air-gap flux density
question: What are factors that determine shaft torque?

answers: text: air-gap area with winding slots and back-iron depth
question: Whate decides the size of an electromagnetic core?

answers: text: magnetic core saturation or safe operating temperature rise and voltage
question: What limits excessive torque?

context: The brushless wound-rotor synchronous doubly-fed (BWRSDF) machine is the only electric machine with a truly dual ported transformer circuit topology (i.e., both ports independently excited with no short-circuited port). The dual ported transformer circuit topology is known to be unstable and requires a multiphase slip-ring-brush assembly to propagate limited power to the rotor winding set. If a precision means were available to instantaneously control torque angle and slip for synchronous operation during motoring or generating while simultaneously providing brushless power to the rotor winding set, the active current of the BWRSDF machine would be independent of the reactive impedance of the transformer circuit and bursts of torque significantly higher than the maximum operating torque and far beyond the practical capability of any other type of electric machine would be realizable. Torque bursts greater than eight times operating torque have been calculated.
qas: answers: text: brushless wound-rotor
question: What is the only device with dual ported transformer circuit topology?

answers: text: both ports independently excited with no short-circuited port
question: What is a brushless wound-rotor?

answers: text: a multiphase slip-ring-brush assembly to propagate limited power to the rotor winding set
question: How does a brushless wound rotor achieve stability?

answers: text: eight times operating torque
question: What is the theoretical maximum of a brushless wound rotor?

context: The continuous torque density of conventional electric machines is determined by the size of the air-gap area and the back-iron depth, which are determined by the power rating of the armature winding set, the speed of the machine, and the achievable air-gap flux density before core saturation. Despite the high coercivity of neodymium or samarium-cobalt PMs, continuous torque density is virtually the same amongst electric machines with optimally designed armature winding sets. Continuous torque density relates to method of cooling and permissible period of operation before destruction by overheating of windings or PM damage.
qas: answers: text: size of the air-gap area and the back-iron depth
question: What determines continuous torque density?

answers: text: power rating of the armature winding set, the speed of the machine, and the achievable air-gap flux density before core saturation
question: What three elements determine the size of the air-gap area and back iron depth?

answers: text: method of cooling and permissible period of operation before destruction by overheating
question: What does continuous torque density refer to?

answers: text: virtually the same
question: How does continuous torque density vary between well designed motors?

context: An electrostatic motor is based on the attraction and repulsion of electric charge. Usually, electrostatic motors are the dual of conventional coil-based motors. They typically require a high-voltage power supply, although very small motors employ lower voltages. Conventional electric motors instead employ magnetic attraction and repulsion, and require high current at low voltages. In the 1750s, the first electrostatic motors were developed by Benjamin Franklin and Andrew Gordon. Today the electrostatic motor finds frequent use in micro-electro-mechanical systems (MEMS) where their drive voltages are below 100 volts, and where moving, charged plates are far easier to fabricate than coils and iron cores. Also, the molecular machinery which runs living cells is often based on linear and rotary electrostatic motors.[citation needed]
qas: answers: text: electrostatic
question: What type of motor is based on the attraction and repulsion of electric charge?

answers: text: conventional coil-based motors
question: What are electrostatic motors like two of?

answers: text: high-voltage
question: What type of power supply do electrostatic motors usually have?

answers: text: Benjamin Franklin and Andrew Gordon
question: What two inventors developed the first electrostatic motors?

answers: text: electrostatic motor
question: Micro-electro mechanical systems prefer what type of motor?