romikgosai/squad_modified huggingface dataset:
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.

Questions and answers:
['
Q: Why do miniature PM motors use high energy magnets?
A: To minimize overall weight and size', '
Q: What are high energy magnets typically made of?
A: neodymium-iron-boron alloy', '
Q: What does the outer housing of a miniature motor resemble?
A: steel tube', '
Q: How do PMs rate against other types of electric motors?
A: least competitive']
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.

Questions and answers:
['
Q: What is the typical maximum range of universal motors?
A: 1000 watts', '
Q: What type of motor was used in trailway traction applications?
A: universal', '
Q: What is the result of using AC power on a DC motor?
A: efficiency losses', '
Q: What were universal motor pole pieces constructed from?
A: solid (un-laminated) iron']
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.

Questions and answers:
['
Q: What kind of motor can employ both AC and DC?
A: universal', '
Q: What component of a universal motor is most likely to fail?
A: commutator', '
Q: When is torque most important in universal motor applications?
A: starting', '
Q: Switching the field winding in washing machines causes the drum to agitate how?
A: forwards and in reverse', '
Q: How is stepped speed control achieved?
A: Multiple taps on the field coil provide']
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.

Questions and answers:
['
Q: At around what RMP do weed trimmer motors operate?
A: 10,000', '
Q: At around what RMP do miniature grinders operate?
A: 30,000', '
Q: What type of motor can universal motors operate much faster than?
A: SCIMs', '
Q: What attributes make universal motors desireable for consumer applications like hair dryers?
A: high speed and light weight']
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.

Questions and answers:
['
Q: What determines the properties of speed and torque?
A: shape of the rotor bars', '
Q: At high speed, where is the most current?
A: interior of the winding', '
Q: Is the current frequency higher or lower at high speed?
A: lower', '
Q: Changing the shapes of the bars creates what?
A: variable resistance', '
Q: Where can variable resistance be created?
A: rotor circuit']
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.

Questions and answers:
['
Q: Where might a resistor be attached?
A: rotor circuit', '
Q: What can a resistor control?
A: motor speed', '
Q: How might wasted power be salvaged?
A: inverter or separate motor-generator', '
Q: From where may a converter be fed?
A: rotor circuit']
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.

Questions and answers:
['
Q: What will a motor do if the load is reduced?
A: speed up', '
Q: What will a motor do if the load is increased?
A: slow down', '
Q: Where are slip losses dissipated?
A: secondary resistors', '
Q: How efficient is such a design?
A: very poor']
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.

Questions and answers:
['
Q: How are torque motors used in computer gaming?
A: feedback steering wheels', '
Q: A torque motor at low voltage provides what?
A: constant light tension', '
Q: A torque motor at high voltage provides what?
A: higher torque', '
Q: In a tape drive, what is not needed if a torque motor is used?
A: gears or clutches']
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.

Questions and answers:
['
Q: What element of a combustion engine does a governor monitor?
A: electrical pulses', '
Q: What is a governor connected to?
A: return spring', '
Q: What kinds of adjustments would a governor make?
A: small', '
Q: What would a governor do to a too-fast running engine?
A: reduce the current being applied to the motor']
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.

Questions and answers:
['
Q: How much slip does a synchronous motor have?
A: zero', '
Q: How does an induction motor produce torque?
A: slip', '
Q: Whithout rotor windings, how must a Hammond clock be started?
A: manually', '
Q: How can a synchronous motor be made more like an induction motor?
A: DC field', '
Q: How is current brought to the rotor in a synchronous motor?
A: Slip rings and brushes']
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.

Questions and answers:
["
Q: What do hysteresis synchronous motors' rotors do when slip rate decreases?
A: becomes temporarily magnetized", '
Q: When in operation, what do hysteresis synchronous motors poles do?
A: stay in place', '
Q: What do hysteresis synchronous motors resemble at startup?
A: induction motors', "
Q: How can a hysteresis synchronous motor's rotor be described?
A: a smooth cylinder", '
Q: What do the distributed poles of a hysteresis synchronous motor resemble?
A: PMSM']
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.

Questions and answers:
['
Q: What type of motor has two independent multiphase winding sets?
A: Doubly fed electric motors', '
Q: What advanage do independent multiphase winding sets have?
A: contribute active (i.e., working) power to the energy conversion process', '
Q: What is one of the independent multiphase winding sets configured for?
A: variable speed operation', '
Q: Doubly fed motors have what advantage over single fed?
A: twice the constant torque speed range']
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.

Questions and answers:
['
Q: A coreless DC motor is distinguished by what?
A: rapid acceleration', '
Q: What is absent in a coreless DC motor?
A: iron core', '
Q: What forms can the rotor take?
A: winding-filled cylinder, or a self-supporting structure']
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.

Questions and answers:
['
Q: What is a likely problem of coreless DC motors?
A: Overheating', '
Q: How does a coreless rotor compare to traditional rotors in terms of weight?
A: lighter', '
Q: What advantage does a coreless rotor have over traditional variants?
A: accelerate much more rapidly', '
Q: The lack of a metal mass in the core causes what function to be absent?
A: heat sink', '
Q: How is a coreless motor cooled?
A: forced air']
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.

Questions and answers:
['
Q: What was the original purpose for pancake motors?
A: drive the capstan(s) of magnetic tape drives', '
Q: What are advantages of pancake motors?
A: minimal time to reach operating speed and minimal stopping distance', '
Q: For what type of military applications are pancake motors currently used?
A: high temperature', '
Q: What type of servo-controlled systems use pancake motors?
A: high-performance']
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.

Questions and answers:
['
Q: What may servo motors be used for?
A: machine tools, pen plotters, and other process systems', '
Q: What must be well understood when applying a servo motor for use?
A: speed, torque, and power', '
Q: What factors limit performance of servo motors?
A: winding inductance and rotor inertia', '
Q: Large, slow servos can use what types of motors?
A: conventional AC or DC motors', '
Q: When might coreless motors be used in servo applications?
A: As dynamic response requirements increase']
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.

Questions and answers:
['
Q: How do servo motors differ from stepper motors?
A: position feedback is continuous', '
Q: How does a stepper system achieve stability?
A: a "home" switch', '
Q: What makes a printer home switch work?
A: position sensor', "
Q: What kind of counter keeps track of a print head's position?
A: bidirectional", "
Q: A stepper system's motor is relied on to not do what?
A: miss steps"]
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.

Questions and answers:
['
Q: When are stepper motors most useful?
A: when precise rotations are required', '
Q: What two devices can describe a stepper motor?
A: DC electric motor and a rotary solenoid', '
Q: What do stepper motor rotors allign themselves with?
A: magnetic field produced by the energized field winding', '
Q: How does a stepper motor differ from a synchronous motor?
A: the stepper motor may not rotate continuously', '
Q: What types of velocities and positions is the stepper motor capable of?
A: forwards or backwards, and it may change direction, stop, speed up or slow down']
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.

Questions and answers:
['
Q: What is a trait of a sophisticated stepper motor?
A: proportionally control the power to the field windings', '
Q: What does proportinal control of the field windings in a stepper motor achieve?
A: rotate extremely smoothly', '
Q: What is another name for smooth rotation?
A: microstepping', '
Q: With what other device are stepper motors most versatile?
A: digital servo-controlled system']
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.)

Questions and answers:
['
Q: Why were stepper motors abandoned in computer drive designs?
A: precision and speed limitations', '
Q: What do newer computer drives use instead of stepper motors?
A: voice coil-based head actuator systems', '
Q: In what direction do modern coil actuators move?
A: perpendicular to the magnetic lines of force', '
Q: To what device does the term, "voice coil" historically refer?
A: the structure in a typical (cone type) loudspeaker']
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.

Questions and answers:
['
Q: List two alternatives to rotary stepper motors in printer applications.
A: linear stepper motors or servomotors', '
Q: In scanners, what do stepper motors move?
A: optical scanning element', '
Q: In printers and copiers, what do stepper motors move?
A: print head carriage (of dot matrix and inkjet printers), and the platen or feed rollers']