Electric_motor

qas: question: What is the largest rating of an electric motor?
answers: text: 100 megawatts

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

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

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

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

question: What is the smallest rating of an electric motor?

question:  What is the main example of a RC power source?

question:  What does EC stand for?

question:  What does DCC stand for?

question:  In what device are large motors least commonly found?
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: question: Who created the first electrostatic device?
answers: text: Andrew Gordon

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

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

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

question: Who created the last electrostatic device?

question: Who discovered the principles of magnetic and electric non-interactions?

question: In what year did Faraday convert non-electrical energy into mechanical energy?

question:  What toxic substance originally didn't serve the function of brine in primitive motors?
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: question: In what year did Jedlik begin experimenting with electromagnetism?
answers: text: 1827

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

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

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

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

question: In what year did Jedlik begin experimenting with non-electromagnetism?

question: Besides the stator and the communicator, what is an element of a non-DC motor?

question:  What didn't Jedlik call his earliest devices?

question:  What discovery solved the problem of non-continuous rotation?

question:  What did Jedlik's improved device make the need for?
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: question: When were developers competing with Jacobi able to match his accomplishments?
answers: text: 1839/40

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

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

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

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

question: When were developers competing with Jacobi able to not match his accomplishments?

question:  What was Jacobi's improved motor used to not propel?

question:  Who created the first fake electric motor?

question:  Who broke the world record set by Jacobi's second motor?

question:  How long did it take for Jacobi's second world record to be broken?
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: question: Who developed the first mnotor capable of being used for machinery?
answers: text: William Sturgeon

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

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

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

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

question: Who developed the last motor capable of being used for machinery?

question:  Which inventor never went bankrupt?

question:  What wasn't the main problem with applying early electric motors to industry?

question:  What necessary technical development always occurred to make electric motors useful?

question:  How slow did Sturgeon and Davenport's motors run?
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: question: What made Pacinotti's motor an important advancement?
answers: text: non-fluctuating current

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

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

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

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

question:  What made Pacinotti's motor an unimportant advancement?

question:  Who created a motor very different from Pacinotti?

question: How similar were the motors in Gramme's demonstrations?

question: Besides a motor, what didn't Gramme use the other device for?

question:  In what two cities did Gramme never conduct his demonstrations?
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: question: What needs to exist between the rotor and stator for increased efficiency?
answers: text: small air gap

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

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

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

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

question: What can't exist between the rotor and stator for increased efficiency?

question:  Which inventor created the first useful DC motor?

question: What was the transportation advancement made impossible by Sprague's designs?

question: What was the name of Chicago's last electric trolley system?

question:  Who did Sprague not work for early in his career?
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: question: How much energy do electric motors use in the modern United States?
answers: text: more than half

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

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

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

question: How much energy do electric motors use in the modern UK?

question: In what domain did electric motors not reduce reliance on humans and animals?

question: Besides shafts, belts and compressed air, what didn't electric motors reduce the need for?

question:  Where didn't electric motors improve convenience and safety?
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: question: Who built the first induction motor?
answers: text: Walter Baily

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

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

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

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

question:  Who built the second induction motor?

question:  What type of power were late motors unable to use?

question:  Who sold Tesla's patents?

question:  For what application was Tesla's motor never used?

question:  What's not another name for the bar-winding-rotor?
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: question: What would a rotor do without current reversal?
answers: text: brake to a stop

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

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

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

question:  What would a rotor do with current reversal?

question:  What switches the output of most DC motors?

question: From where is current to the motor not supplied?

question:  What two motor types are descendant today?
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: question: What does the communicator do?
answers: text: reverses the flow of current in the rotor windings

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

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

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

question: What does the excommunicator do?

question:  What type of current is featured in brushed RC motors?

question: Where do brushes not get their power?

question:  What is not the main feature of the shaft in a commutated DC motor?
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: question: Current flowing to create a temporary magent is called what?
answers: text: electromagnet

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

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

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

question: Current flowing to create a non-temporary magent is called what?

question:  What doesn't rotate the motor shaft?

question:  What element of the motor makes the poles alligning?

question: What motor device demonstrates why a commutator is needed?
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: question: How is RFI generated?
answers: text: sparking

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

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

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

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

question: How is RFID generated?

question:  What don't brushes need to be in contact with?

question:  What is not created by contact between parts of the motor?

question:  What does sparking not limit?

question: What motor components least need replacement and maintenance?
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: question: What are large brushes favorable for?
answers: text: motor output

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

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

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

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

question: What are small brushes favorable for?

question: What are small brushes not favorable for?

question:  What type of brushes are not the cheapest?

question:  How can the speed of larger brushes be decreased?

question:  Besides wear, what is a upside of stiff brush springs?
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: question: What can a PM motor not be adjusted for?
answers: text: speed control

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

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

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

question:  What can a PMM motor not be adjusted for?

question:  What is another name for PMM fields?

question:  What design feature does a PMM motor lack?

question:  What don't field windings provide?
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: question: Why do miniature PM motors use high energy magnets?
answers: text: To minimize overall weight and size

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

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

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

question: Why do large PM motors use high energy magnets?

question:  What are high energy magnets never made of?

question:  What doesn't the outer housing of a miniature motor resemble?

question:  How do PMs rate with other types of electric motors?
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: question: What is the typical maximum range of universal motors?
answers: text: 1000 watts

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

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

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

question: What is the atypical maximum range of universal motors?

question:  What type of motor was not used in trailway traction applications?

question: What is the result of using DC power on a DC motor?

question: What weren't universal motor pole pieces constructed from?
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: question: What kind of motor can employ both AC and DC?
answers: text: universal

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

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

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

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

question:  What kind of motor can employ both DC and DC?

question: What component of a universal motor is most likely to not fail?

question:  When is torque least important in universal motor applications?

question: Switching the field winding out of washing machines causes the drum to agitate how?
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: question: At around what RMP do weed trimmer motors operate?
answers: text: 10,000

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

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

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

question:  At around what RRP do weed trimmer motors operate?

question:  At around what RMR do miniature grinders operate?

question: What type of motor can't universal motors operate much faster than?

question: What attributes make universal motors less desirable for consumer applications like hair dryers?
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: question: What determines the properties of speed and torque?
answers: text: shape of the rotor bars

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

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

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

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

question: What doesn't determine the properties of speed and torque?

question:  At low speed, where is the most current?

question:  Is the non-current frequency higher or lower at high speed?

question: Not changing the shapes of the bars creates what?

question:  Where can variable resistance not be created?
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: question: Where might a resistor be attached?
answers: text: rotor circuit

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

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

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

question: Where might a resistor not be attached?

question:  What can a resistor never control?

question:  How might wasted power not be salvaged?

question:  From where won't a converter be fed?
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: question: What will a motor do if the load is reduced?
answers: text: speed up

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

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

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

question:  What will a motor do if the load is not reduced?

question:  What will a motor do if the load is decreased?

question:  Where are slip losses not dissipated?

question: How inefficient is such a design?
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: question: How are torque motors used in computer gaming?
answers: text: feedback steering wheels

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

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

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

question: How aren't torque motors used in computer gaming?

question:  A torque motor at high voltage provides what?

question:  A torque motor at low voltage provides what?

question:  In a tape drive, what is needed if a torque motor is used?
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: question: What element of a combustion engine does a governor monitor?
answers: text: electrical pulses

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

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

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

question:  What element of a combustion engine doesn't a governor monitor?

question:  What is a governor disconnected from?

question:  What kinds of adjustments would a governor never make?

question:  What would a governor do to a too-slow running engine?
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: question: How much slip does a synchronous motor have?
answers: text: zero

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

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

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

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

question: How much slip does a non-synchronous motor have?

question:  How doesn't an induction motor produce torque?

question:  With rotor windings, how must a Hammond clock be started?

question:  How can a synchronous motor be made less like an induction motor?

question:  How isn't current brought to the rotor in a synchronous motor?
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: question: What do hysteresis synchronous motors' rotors do when slip rate decreases?
answers: text: becomes temporarily magnetized

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

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

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

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

question: What do hysteresis synchronous motors' rotors do when slip rate increases?

question: When in operation, what don't hysteresis synchronous motors poles do?

question: What do hysteresis synchronous motors not resemble at startup?

question:  How can't a hysteresis synchronous motor's rotor be described?

question: What do the undistributed poles of a hysteresis synchronous motor resemble?
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: question: What type of motor has two independent multiphase winding sets?
answers: text: Doubly fed electric motors

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

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

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

question:  What type of motor has three independent multiphase winding sets?

question:  What advantage don't independent multiphase winding sets have?

question: What is one of the dependent multiphase winding sets configured for?

question:  Doubly fed motors have what disadvantage under single fed?
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: question: A coreless DC motor is distinguished by what?
answers: text: rapid acceleration

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

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

question:  A coreless RC motor is distinguished by what?

question:  What is absent in a coreless RC motor?

question:  What forms can't the rotor take?
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: question: What is a likely problem of coreless DC motors?
answers: text: Overheating

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

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

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

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

question: What is a likely problem of coreless RC motors?

question: How does a coreless rotor not compare to traditional rotors in terms of weight?

question: What advantage doesn't a coreless rotor have over traditional variants?

question:  How is a coreless motor warmed?

question: The surplus of a metal mass in the core causes what function to be absent?
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: question: What was the original purpose for pancake motors?
answers: text: drive the capstan(s) of magnetic tape drives

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

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

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

question: What was the original purpose for waffle motors?

question:  What are advantages of waffle motors?

question: For what type of military applications are waffle motors currently used?

question:  What type of servo-controlled systems use waffle motors?
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: question: What may servo motors be used for?
answers: text: machine tools, pen plotters, and other process systems

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

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

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

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

question:  What may servo motors never be used for?

question: What must not be well understood when applying a servo motor for use?

question:  What factors don't limit performance of servo motors?

question:  Small, fast servos can use what types of 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: question: How do servo motors differ from stepper motors?
answers: text: position feedback is continuous

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

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

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

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

question: How are servo motors the same as stepper motors?

question:  How does a stepper system not achieve stability?

question:  What makes a printer home switch break?

question:  What kind of counter keeps track of a print foot's position?

question:  A stepper system's motor is unrelied on to not do what?
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: question: When are stepper motors most useful?
answers: text: when precise rotations are required

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

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

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

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

question:  When are stepper motors least useful?

question:  What three devices can describe a stepper motor?

question:  What do stepper motor rotors align themselves without?

question:  How doesn't a stepper motor differ from a synchronous motor?
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: question: What is a trait of a sophisticated stepper motor?
answers: text: proportionally control the power to the field windings

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

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

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

question:  What is not a trait of a sophisticated stepper motor?

question: What doesn't proportional control of the field windings in a stepper motor achieve?

question:  What is another name for rough rotation?

question:  With what other device aren't stepper motors most versatile?
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: question: Why were stepper motors abandoned in computer drive designs?
answers: text: precision and speed limitations

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

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

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

question: Why weren't stepper motors abandoned in computer drive designs?

question:  What don't newer computer drives use instead of stepper motors?

question:  In what direction don't modern coil actuators move?

question: To what device does the term, "voice coil" not historically refer?
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: question: List two alternatives to rotary stepper motors in printer applications.
answers: text: linear stepper motors or servomotors

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

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

question: List two alternatives to rotary stepper motors in non-printer applications.

question:  In scanners, what don't stepper motors move?

question:  In printers and copiers, what don't stepper motors move?
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: question: Voltage opposing the motor supply voltage is called what?
answers: text: back electromotive force

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

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

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

question: Voltage not opposing the motor supply voltage is called what?

question:  ENP is proportional to what?

question:  Voltage at the brushes is not equal to what?

question: If load decreases, what happens to current drawn?
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: question: What needs to be known to calculate torque?
answers: text: fields in the air gap

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

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

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

question:  What needs to be unknown to calculate torque?

question:  How are the very few calculations to determine torque done?

question: How is torque undetermined?

question:  What is the formula to not determine torque?
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: question: What are factors that determine shaft torque?
answers: text: torque current), voltage, pole-pair number, excitation frequency (i.e., synchronous speed), and air-gap flux density

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

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

question: What aren't factors that determine shaft torque?

question:  Whate decides the size of a nonelectromagnetic core?

question:  What doesn't limit excessive 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: question: What is the only device with dual ported transformer circuit topology?
answers: text: brushless wound-rotor

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

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

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

question: What is the only device with triple ported transformer circuit topology?

question:  What is a brushfilled wound-rotor?

question: How doesn't a brushless wound rotor achieve stability?

question:  What isn't the theoretical maximum of a brushless wound rotor?
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: question: What determines continuous torque density?
answers: text: size of the air-gap area and the back-iron depth

question: What three elements determine the size of the air-gap area and back iron depth?
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 does continuous torque density refer to?
answers: text: method of cooling and permissible period of operation before destruction by overheating

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

question: What determines non-continuous torque density?

question:  What is the fourth element that determines the size of the air-gap area and back iron depth?

question:  What doesn't continuous torque density refer to?

question: How does non-continuous torque density vary between well designed motors?
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: question: What type of motor is based on the attraction and repulsion of electric charge?
answers: text: electrostatic

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

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

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

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

question: What type of motor is not based on the attraction and repulsion of electric charge?

question: What are electrostatic motors like three of?

question:  What type of power supply don't electrostatic motors usually have?

question:  What two inventors developed the second electrostatic motors?

question:  Macro-electro mechanical systems prefer what type of motor?
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]