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Techical performance of the traction machine design

rotating magnetic field as a sum of magnetic vectors from 3 phase coils.

An electric motor converts electrical energy into kinetic energy. The reverse task, that the conversion kinetic energy into electrical energy, is accomplished by a generator or alternator. In many cases the two devices differ only in their application and details minor construction, and some applications use a single device to fill both roles. For example, traction motors used on locomotives made often both tasks if the locomotive is equipped with dynamic brakes.

Operation

Most electric motors work by electromagnetism, but motors based on other electromechanical phenomena, such as electrostatic forces and the piezoelectric effect, also exist. The fundamental principle upon which electromagnetic motors are based is that a mechanical force on any current-carrying wire contained within of a magnetic field. The force is described by the law of the Lorentz force and is perpendicular to both the wire and the magnetic field. Most magnetic motors are rotary, but linear motors also exist. In a rotary engine, the rotating part (usually on the inside) is called the rotor, and the stationary part is called the stator. The rotor turns because cables and magnetic field are arranged so that a couple develops on the rotor shaft. The motor contains electromagnets that are placed in a frame. Although this framework is often called the armature, that term is often erroneously applied. Correctly, the armature is the part of the engine through which it supplies the input voltage. Depending the design of the machine, either the rotor or the stator can serve as the armature.

DC motors

Electric motors of various sizes.

One of the first electromagnetic rotary engine was invented by Michael Faraday in 1821 and consisted of a free-hanging wire dipping into a pool of mercury. A permanent magnet was placed in the middle of the pool of mercury. When a current was passed through the cable, the cable goes around the magnet, showing that the current resulted in a circular magnetic field around the wire. This engine is shown often in physics classes in school, but brine (salt water) is sometimes used instead of toxic mercury. This is the simplest form of a class of engines electric motors called homopolar. A further refinement is the wheel of Barlow.

Another original design of the electric motor uses a reciprocating piston within a solenoid switching, conceptually it could be viewed as an electromagnetic version of a two-stroke internal combustion.

The modern DC motor was invented by accident in 1873, when Gramme connected a dynamo Zénobe moving into a second similar unit, driving as a motor.

The classic DC motor has a rotating armature in the form of an electromagnet. A rotary switch called a commutator reverses the direction of the electric current twice per cycle, to flow across the armature to the poles of the electromagnet push and pull against the permanent magnets outside of the engine. As the poles of the armature electromagnet pass the poles of permanent magnets, the switch reverses the polarity of the electromagnet armature. During that moment of change of polarity, inertia keeps the engine is classic in the right direction. (See diagrams below.)

A single engine power. When the coil current, a magnetic field is generated around the armature. The left side of the armature away from the left and magnet attracted to the right, causing rotation.

The armature continues to rotate.

When the armature becomes horizontally aligned, the switch reverses the direction of current through the coil, the magnetic field reversed. The process is then repeats.

field wound DC motor

The permanent magnets on the outside (stator) of a DC motor continuous may be replaced by electromagnets. By varying the field current is possible to alter the speed / torque motor. Typically, the field winding are placed in series (series wound) with the armature winding for high torque at low speed, in parallel (shunt wound) with the armature for high speed low torque engine, or to have a settlement, in parallel, and partly in series (compound wound) a balance that gives a constant speed on a range of loads. Additional reductions in the current field are possible to gain speed even more, but proportionately smaller pair called "weak field" operation.

Theory

If the shaft of a DC motor is activated by an external force, the motor acts as a generator and produce an electrical driving force (EMF). This voltage is also generated during normal engine operation. The spinning motor produces a voltage known as back EMF because it opposes the applied voltage to the motor. Therefore, the voltage drop across a motor consists of the voltage drop due to this new CMS and the parasitic voltage drop resulting from the internal resistance apperature the windings. The current through a motor is given by the following equation:

I = (Vapplied? Vbackemf) / Rapperature-

The mechanical energy produced by the motor is equal to:

P = I * Vbackemf-

Since the back emf is proportional to the speed engine, when an electric motor starts or stops completely, back EMF is zero. Therefore, the current through the apperature is much higher. This high current yield a strong electric field to start the engine turning. As the motor turns, the back EMF increases to be equal to the applied voltage minus the parasitic voltage drop. At this point there will be a small current flowing through the engine. Basically these three equations can be used to find the speed, power and return EMF of an engine load:

Load = Vbackemf * I-

Rapperature Vapplied = I *? Vbackemf-

Vbackemf = speed * Fluxapperature-

Speed Control

In general, the speed of rotation of a DC motor is proportional to voltage applied to it, and the torque is proportional to the current. Speed control can be achieved by variable battery outlets, the variable supply voltage, resistance or electronic controls. The address of a wound field DC motor can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors).
The effective voltage can be varied by inserting a resistor in series or a controlled device electronically changed his thyristors, transistors, or, formerly, mercury arc rectifiers. In a circuit known as a switch, the average voltage applied the motor is varied by changing the voltage rapidly. As the "on" to "off" duty cycle ratio () is varied to alter the average voltage applied, the engine speed varies. The percentage "on" time multiplied by the supply voltage gives the voltage average applied to the motor. Therefore, a supply of 100 V and 25% "on" time average voltage at the motor is 25 V. During the 'off' time, motor current flows through a diode called a diode wheel. " At this point in the cycle of current will be zero, and therefore the average motor current always exceed the current offer unless the percentage of "on" time is 100%. 100% "on" time of supply and current motor are equal. The rapid change loses less energy than series resistors. output smoothing filters average voltage applied to the motor and reduce motor noise. This method also known as pulse width modulation or PWM, and is often controlled by a microprocessor.

Since the DC series wound motor develops its highest torque at low speed, it is often used in traction applications such as electric locomotives and trams. Another application is starter motors for petrol and diesel engines small. series engines should never be used in applications where the unit may fail (eg belt drives). As the motor accelerates, the armature (and hence field) current is reduced. The reduction in the field causes the motor to speed up (see the 'weak' in the previous section) until it is destroyed. This can also be a problem with the train engine in the event of a loss of adhesion, since, unless quickly brought under control, engine can reach speeds much higher than they would in normal circumstances. Not only can this cause problems for the engines themselves and dresses, but due to the difference speed between the rails and wheels can also cause severe damage to the rails and treads of the wheel, as the heat and cool quickly. field weakening is used in some electronic controls to increase the speed of an electric vehicle. The simplest form uses a contactor and field weakening resistance, electronic control monitors the motor current and switches the field weakening resistance in the circuit when the motor current drops below a preset (This is when the engine is at its design speed). Once the resistance is in the motor circuit will increase the speed above the speed normal rated voltage. When you increase the motor current control is disconnected from the resilience and low-speed torque is made available.

One method interesting speed control of DC motor is the Ward Leonard control. It is a method for controlling a DC motor (usually a shunt or compound wound) and developed as a method of providing an engine speed controlled AC power supply, though not without its benefits in DC plans. The AC is used to push for a AC motor, usually an induction motor that drives a DC generator or dynamo. The DC output is connected directly armor to the motor armature current (usually the same building). The shunt field windings of both DC machines are driven through a variable resistance of the armature of the generator. This resistance variable speed control provides very stop good speed, and torque consistent. This control method was the de facto method from its development until it was replaced by solid state thyristor systems. Saw service in almost any environment where control is required speed, ranging from passenger lifts through to the big head pit mine shafts and even industrial process machinery and electric cranes. Its main disadvantage is that three machines were required to implement a scheme (five in very large installations, such as DC machines often doubled and controlled by a variable Tandem resistance). In many applications, the motor-generator set was often permanently to avoid delays that would otherwise be caused by putting in up as needed. There are numerous legacy Ward-Leonard facilities still in service.

Universal motors

A variant of the wound field DC motor is the universal motor. The name derives from the fact that you can use the air conditioning or DC power supply, although in practice almost always used with AC current. The principle is that in a field of DC motor, current wound both in the field and armature (and hence the resulting magnetic fields) will alternate (Reverse polarity) at the same time, and therefore the mechanical force generated is always in the same direction. In practice, the motor must be specially designed to cope with the alternating current (impedance must be considered as pulsating force), and the resultant motor is generally less efficient than an equivalent pure DC motor. That operating at normal frequency of the power line, the maximum output of universal motors is limited and motors exceeding one kilowatt are rare. However, universal motors also form the basis of traditional railway traction motor. In this application, to maintain their high electrical efficiency, which were operated supply AC low frequency of 25 Hz and 16 2 / 3 hertz operation being common. Because they are universal motors, locomotives of this design were also commonly capable of operating from a third rail powered by DC.

The advantage of the universal motor is that AC supplies may be used in engines that have the characteristics Typical DC motors, specifically high starting torque and very compact design if high running speeds are used. The downside is the maintenance and problems in the short life caused by the collector. As a result of these motors are usually used in AC devices such as mixers and power tools which are only used intermittently. continuous monitoring of the speed of a universal motor running on AC is very easy to perform using a thyristor circuit, while intensified the speed control can be accomplished using multiple taps on the coil field. Household blenders that advertise many speeds frequently combine a field coil several taps and a diode that can be inserted in series with the motor (causing the engine to operate with half-wave current with half of the RMS voltage line AC power).

Unlike AC motors, universal motors can easily exceed one revolution per cycle of the mains. This makes them useful for appliances such as blenders, vacuum cleaners and hair dryers when you want a high-speed performance. Many vacuum cleaner and weed trimmer motors exceed 10,000 rpm, Dremel and other similar miniature grinders often in excess of 30,000 rpm. A theoretical universal motor allowed to operate without mechanical load speeding, which can damage. In real life, although having different friction, the armor "wind effect" and the burden of any act integrated cooling fan to prevent speeding.

With the low cost of semiconductor rectifiers, some applications that previously used a universal motor now use a pure DC motor, usually with a permanent magnetic field. This is especially true if the semiconductor circuit is also used for speed control variable.

The advantages of universal motor and AC power distribution made the installation of a low-frequency drive current distribution system economic for some railway facilities. At sufficiently low frequencies, the engine performance is about the same as if the engine is operating on DC. Frequencies as low as 162 / 3 hertz is used.

AC motors

In 1882, Nikola Tesla defined the rotation of the magnetic field and pioneered the use of a rotating field of force to operate machines. It exploits the principle of designing an induction only two motor phases in 1883. In 1885, Galileo Ferraris independently researched the concept. In 1888, Ferraris published his research in a paper to the Royal Academy Science of Turin.

Introduction of Tesla's motor from 1888 onwards initiated what is known as the Second Industrial Revolution, making possible efficient generation and long distance electrical power distribution with alternating current transmission system, also of Tesla's invention (1888) [A]. Before the invention of the rotating magnetic field, motors operated by a driver who passes continuously through a fixed magnetic field (as in homopolar motors).

Tesla had suggested that the switches of a machine can be removed and the device may operate in a rotating field of force. Professor Poeschel, his teacher said it would be like building a perpetual motion machine. [2] Tesla later reach U.S. Patent 0416194, Electric Motor (December 1889), it seems that the engine is seen in many photos of Tesla. This classic alternating current electro-magnetic motor was a

motor induction.

Stator power

Rotor power

total energy supplied

Power developed

10

90

90

900

50

50

100

2500

In the induction motor, the field and the armature is ideally positioned to field forces and the field of equality and armature cores were of equal size. The total energy to operate the device equaled the sum of the energy expended in the armature and field coils. [3] The power developed in operation the device equaled the product of the energy expended in the armature and field coils. [4]

Michail Osipovich Dolivo-Dobrovolsky later invented a three phase "cage-rotor" in 1890. A successful trading system polyphase generation and transmission over long distances was designed by Mill Creek Decker Almeria No. 1 [5] in Redlands California. [6]

Components and types

A typical AC motor consists of two parts:
1. A stationary stator coils outside the AC power supplied to produce a rotating magnetic field, and;
2. An inside rotor coupled to the output shaft that is given a pair by the rotating field.

There are two basic types of alternating current motor depending on the type of rotor used:

• The synchronous motor, which rotates exactly at the supply frequency or a submultiple of feeding frequency, and;
• The induction motor, which is a little slower, and usually (though not necessarily always) takes the shape of a squirrel cage motor.

Three-phase AC induction motors

Three phase AC induction motors with 1 Hp (746 W) and 25 W with small engine CD player, toys and CD / DVD head cross

Where a polyphase electrical supply is available, the three phases (or polyphase) induction motor is commonly used, especially for high power engines. The phase differences between the three phases of power polyphase create an electromagnetic field in rotating machinery.

Through electromagnetic induction, the rotating magnetic field induces current in the conductors in the rotor, which in turn creates a magnetic field as a counterweight which makes the rotor turn in the direction the field is rotating. The rotor must always rotate slower than the rotating magnetic field produced by the polyphase electrical supply, otherwise, no counterbalancing field will occur in the rotor.

Induction motors are the workhorses of industry and engines up to 500 kW (670 hp) of output produced in sizes highly standardized structure, making them nearly completely interchangeable between manufacturers (although European and American standard dimensions are different.) Very large synchronous motors are capable of tens of thousands of kilowatts of output gas compressor units and wind tunnel. There are two types of rotors used in motors induction.

Squirrel-cage rotors: Most AC motors in common use squirrel cage rotor, which found in virtually all light industrial alternating current motors and domestic. The squirrel cage takes its name from its shape - one ring on each end of the rotor, bars connecting the rings running the length of the rotor. It is usually aluminum or copper poured between the iron laminates of the rotor, and usually only rings final be visible. The vast majority of the rotor currents will flow through the bars instead of the highest resistance and usually varnished laminates. Very low voltages in very high flows are typical in the bars and end rings, high-efficiency motors often use copper smelter to reduce resistance in the rotor.

In operation, the squirrel cage motor can be viewed as a transformer with a rotating secondary - when the rotor does not rotate in sync with the magnetic field, large rotor currents are induced, the large rotor currents magnetize the rotor and interact with the magnetic fields of the stator to the rotor in synchronization with the stator field. A squirrel cage motor at synchronous speed downloads will only consume power to maintain rotor speed against friction and resistance losses, as the mechanical load increases, so will the electrical load - the electrical load is inherently related to the load mechanics. This is similar to a transformer, which is related to the electrical charge of the primary to secondary electric charge.

So, for example, a squirrel-cage fan motor can cause the lights to dim in a house when it starts, but not dim the lights when your fanbelt (and therefore mechanical load) is removed. Furthermore, a stalled squirrel cage motor (overloaded or stuck with a shaft) will consume current limited only by circuit resistance in their attempt to start. Unless something else limits the current (or cuts it completely) overheating and destruction of the winding insulation is the likely result.

Virtually all washing machines, dishwashers, independent fan, player, etc. uses some variant of a squirrel motor housing.

Rotor winding: An alternative design, called the wound rotor, is used when variable speed is required. In this case, the rotor has the same number of poles as the stator windings wire, connected to slip rings on the shaft. The coals slip rings connected to an external controller, such as a variable resistor that changes the slip rate engine. In a high power variable speed drives wound rotor, slip frequency energy is captured, rectified and returned to the power supply through an inverter.

Compared to squirrel cage rotors, wound rotor motors are expensive and require maintenance slip rings and brushes, but they were the standard form for variable speed control before the advent of compact power electronic devices. Transistorized inverters with variable frequency can be now be used for speed control and wound rotor motors are becoming less common. (Transistorized inverter drives also allow more efficient three phase motors to be used if one network is available stage, but this is never used in the devices are home, because it can cause electrical interference and because of high power requirements.)

Several methods of starting a polyphase motor are used. When large current inrush and high torque can be permitted, the engine can be started across the line, by applying full line voltage to the terminals. Where necessary to limit inrush startup (Where the motor is large compared with the ability to short of supply), reduced voltage starting using series inductors, an autotransformer, thyristors, or other devices are used. A technique sometimes used is wye-delta starting, where the motor coils are initially connected to the acceleration load, then switched to delta when the load reaches its speed. This technique is more common in Europe than North America. Transistor leads directly the applied voltage may vary as required by the motor starting characteristics and the load.

This type of motor is becoming more common traction applications such as locomotives, where it is known as the asynchronous traction motor.

The speed of AC motor is determined primarily by the frequency of AC power and the number of poles in the stator winding, according to the relationship:

Ns = 120F / P

where
Ns = synchronous speed in revolutions per minute
F = AC power frequency and
p = Number of poles per phase winding

Actual RPM induction motor will be less than that calculated by the synchronous speed and slip a known quantity that increases with the torque produced. No load, Speed is very close to the sync. When loaded, standard motors have between 3.2% slip, special motors may have up to 7% slip, and a class motors known as torque motors are rated for operation at 100% slip (0 RPM / full stop).
The AC motor slip is calculated by:

S = (N? N °) / Ns

where
N = rotational speed in revolutions per minute.
S = Slip normalized, 0-1.

For example, a typical four-pole motor running at 60 Hz may have a rating of 1725 RPM at full load, while its calculated speed is 1800.

The speed in this engine has traditionally have been altered by new sets of coils or poles in the motor can be switched on and off to change the speed rotation of the magnetic field. However, advances in power electronic means the frequency of the power supply can now be varied to provide smoother control motor speed.

Three-phase AC synchronous motors

If connections the rotor windings of a three phase motor are taken out of the ring and fed a separate field current to create a permanent magnetic field (or if the rotor is formed by a permanent magnet), the result is called a synchronous motor because the rotor rotates in synchronism with the rotating magnetic field produced by power polyphase.

The synchronous motor can also be used as an alternator.

Nowadays, synchronous motors are often transistor driven by frequency inverters. This greatly eases the problem of starting the massive rotor of a large synchronous motor. You can also start as induction motors using a squirrel cage winding that shares the common rotor: once the motor reaches synchronous speed, no current is induced in the squirrel cage winding so it has little effect on the operation of the synchronous motor, stabilizing the engine speed at load changes.

Synchronous motors are sometimes used as traction motors, high-speed train can be the best known example of such use.

Two phases AC servo motors
A typical two-phase AC servo motor has a squirrel-cage rotor and a field consisting of two coils: a) a voltage constant (AC) main winding, and 2) a control-voltage (AC) winding in quadrature with the main winding to produce a rotating magnetic field. Resistance electrical rotor is intentionally high so that the torque-speed curve is fairly linear. Two stages are inherently high-speed servo motors, low torque devices, oriented largely down to lead the charge.

Single-phase AC induction motors

Three-phase motors inherently produce a rotating magnetic field. However, when only single phase power is available, the rotating magnetic field must produced by other means. Several methods are commonly used.

A common motor is single phase shaded pole motor, which is used in devices requiring low torque, such as electric fans or other small appliances. In this motor, small single-turn copper "shading coils "create the moving magnetic field. A portion of each pole is surrounded by a copper coil or strap, the current induced in the strap opposes the change of flow through the coil (Lenz's law), so that movements of maximum field strength across the pole face on each cycle, producing the magnetic field required rotation.

Another common single-phase AC induction motor is the split-phase, commonly used in critical applications such as washing machines and clothes dryers. Compared to the shaded pole motor, these motors can generally provide higher starting torque with a special startup winding in relation with a centrifugal switch.

In split-phase motors, the start winding has been designed with a high resistance winding up. This creates a LR circuit which slightly shifts the phase of current at start of liquidation. With the engine starting, the start winding is connected to the power powered by a set of spring contacts under pressure from the not-yet-rotating centrifugal switch. The starting winding is wound with fewer turns small wire from the main settlement and therefore has a low inductance (L) and increased resistance (R). The lower the ratio L / R creates a gap small, not more than about 30 degrees between the flow due to the main winding and starting winding flow. The start address of the rotation can be reversed simply exchanging the connections of the implementation of settlement in relation to the windings.

The phase of the magnetic field at the start of liquidation phase shifts of the grid, allowing the creation of a moving magnetic field that starts the engine. Once the motor reaches near design operating speed, the centrifugal switch activates, opening the contacts and disconnecting the start winding of the power supply. The motor works only the windings. The starting winding must be disconnected since it would increase the losses in the motor.

In a start motor capacitor, capacitor boot is inserted in series with the beginning of settlement, the creation of an LC circuit that is capable of a phase change is much higher (and therefore a higher starting torque). The capacitor naturally adds costs for these engines.

Another variation is the Permanent Split-Capacitor (PSC) motor (also known as a capacitor starting and running engine). This engine works similarly to the capacitor-start motor described above, but there is no centrifugal starting switch and the second winding is permanently connected to the power supply. PSC motors are frequently used in air handling, fans, blowers and other cases where a variable desired speed. By changing taps on the running winding but keeping the load constant, the motor can be forced to run at different speeds. Also provided all winding connections are available separately in June, a 3 phase motor can be converted into a capacitor start and run the engine for two of the windings commoning and connecting the third via a capacitor to act as a starting point of liquidation.

Repulsion motors are wound-rotor single-phase motors AC that are similar to universal motors. In a repulsion motor, the armature brushes are shorted instead of connecting in series with the field. There Several types of repulsion motors have been manufactured, but the repulsion-start induction of management (RS-IR) engine has been used more frequently. The RS-IR motor has a centrifugal switch that shorts all segments of the switch so that the engine runs as an induction motor, once it has accelerated to full speed. RS-IR engines have been used to provide high starting torque per ampere under conditions of cold operating temperatures and poor source voltage regulation. Few engines repulsion of any kind are sold after 2006.

Single-phase AC synchronous motors

The Small AC single phase motors also can be designed with magnetized rotors (or variations on this idea). The rotors of these motors require no power induced so they will not slip backward against the mains frequency. Instead, rotate synchronously with the mains frequency. Due to its high accuracy rate, these engines are generally used to mechanical clocks, audio courses, and tape drives, previously used were also very high precision instruments clock, as the band recorders or telescope drive mechanisms. The shaded pole synchronous motor is one version.

Because inertia makes it difficult for instantly accelerate rotor synchronous speed stopped, these motors normally require some type of feature to start. Various designs use a small induction motor (which can share the same field coils and rotor as the synchronous motor) or a very light rotor with a one-way mechanism (to ensure that the rotor starts in the "forward" direction).

Torque motors

A torque motor is a specialized form of induction motor that is capable of operating indefinitely at the position (locked-rotor turning) without damage. In this mode, the engine applies a constant torque load (hence the name). A common application of a torque motor would be the supply and take-up reel motors in a unit tape. 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 if the capstan is feeding tape past the tape heads. Driven from a higher voltage (and thus deliver more torque), the torque motors can also be achieved fast forward and rewind without additional mechanics such as gears or clutches.

Stepper motors

Closely related to the design of three-phase AC synchronous motors are stepper motors, where an internal rotor containing permanent magnets or a large iron core with salient poles is controlled by a set of external magnets that are connected electronically. A stepper motor can also be considered as a cross between an electric motor DC and a solenoid. As each coil is energized in turn, the rotor aligns itself with the magnetic field produced by the energy field of liquidation. Unlike a synchronous motor, in its application, the engine can not rotate continuously, but "steps" from one position to the next as field coils is energized and no current in sequence. Depending on the sequence, the rotor can rotate forward or backward.

Simple stepper motor drivers entirely or completely de-energize power the field winding, bringing the rotor to "cog" to a limited number of positions, more sophisticated drivers can proportionally control the power of the field coils to allow the rotors to position "between" the "gear" points and thereby rotate extremely smoothly. The stepper motors controlled computer is one of the most versatile forms of positioning systems, especially when part of a digital servo control.

Stepper motors can rotate in a specific angle with ease, and hence stepper motors are used in computer disk drives, where high precision is required to provide for the proper functioning of, for example, a hard drive or CD.

Permanent Magnet Motor

A permanent magnet motor is the same as the conventional dc machine, except that the field winding is replaced by permanent magnets. In doing so, the machine could act as a machine of constant excitation direct current (dc machine separately excited).

These engines often have a number of small, ranging up to a power low. They are used in small appliances, cell vehicles, for medical purposes, in other medical equipment such as X-ray machines. These engines are also used toys, cars and auxiliary engines for the purpose of seat adjustment, electric windows, mirror adjustment and the like.

Brushless DC motors

Many of the limitations of the classical switch DC motor due to the need for brushes to press against the commutator. This creates friction. At higher speeds, brushes have greater difficulty maintaining contact. Brushes may bounce off the irregularities in the commutator surface, creating sparks. This limits the maximum speed of the machine. The current density per unit area of the brushes limits the motor output. The imperfect electric contact also causes electrical noise. Brushes wear out and require replacement, and collector itself is subject to wear and maintenance. The switch assembly to a large machine is a costly element, requiring precision assembly from many quarters.

These problems are eliminated in the brushless motor. In this engine, the mechanic "rotation" switch or switch / assembly brushgear is replaced by an external electronic switch synchronized with the engine position. brushless motors are typically 85-90% efficiency, while the engine DC with brushgear are typically 75-80% efficient.

In between regular DC motors and stepper motors lies the realm of brushless DC motor. Built in a way very similar to stepper motors, these often use a permanent magnet external rotor, three phases of driving coils, one or more Hall effect devices to sense the position of the rotor and associated drive electronics. The coils are activated, the stage one after another, by electronic car as guidelines for the signals of Hall effect sensors. In fact, three-phase synchronous motors act as its own electronics unit variables frequency. A special kind of DC motor controllers, brushless feedback sensors used by the CMS main phase connections instead of Hall effect to determine the position and speed. These engines are widely used in radio controlled electric vehicles.

Brushless motors DC are commonly used where precise speed control is necessary, computer disk drives or in video cassette recorders within the lines of CD, CD-ROM (etc.) drives, and mechanisms within office products such as fans, laser printers and photocopiers. They have several advantages over conventional motors:

• Compared to AC fans shaded-pole motors, which are very efficient, running much cooler than current motors equivalent alternative. This cool operation leads to life much better than the bearings of the fan.
• Without a collector to carry out the life of a DC motor Brushless may be significantly higher compared with a DC motor with a brush and commutator. Switching also tends to cause a large amount of RF power and noise, without a commutator and brushes, a brushless motor can be used in sensitive electrical devices audio equipment or computers.
• The same hall effect devices providing commutation can also provide a tachometer signal suitable for closed loop control (servo-control) applications. In fans, the tachometer signal can be used to derive a
• fan well "signal.
• The engine can be easily synchronized with an internal clock or external, to achieve a precise control of speed.
• Brushed motors can not be used in the vacuum of space, since being welded in a unmovable position.
  DC motors brushless modern range in the power of a fraction of a watt to many kilowatts. larger brushless motors up to approximately 100 kW are used in electric vehicles. They also find significant use of high-performance electric model aircraft.

DC motors without core

Nothing in the design of one of the motors described above requires that the iron (steel) portions of the rotor actually rotate; pair only exerted on the coils of electromagnets. Taking advantage of this fact is the DC motor without a nucleus, a specialized form of a DC brush 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 cylinder filled with settlement inside the stator magnets, a basket surrounding the stator magnets, or a tortilla (possibly formed on a printed circuit board) running between upper and lower stator magnets. The windings are typically stabilized by being impregnated with epoxy.

Since the rotor is much lighter weight (weight) a conventional rotor formed from copper coils of steel sheet, the rotor can accelerate much more rapidly, often achieving a mechanical time constant 1 ms. This is especially true if the use of coils of aluminum instead of copper heavier. 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.

These motors were commonly used to drive the capstan (s) of magnetic tape drives and are widely used in high performance servo systems.

Linear Motors

A linear motor is basically an electric motor that has been "unrolled" so that instead of producing a torque (rotation), which produces a linear force along its length by setting an electromagnetic field trip.

Linear motors are induction motors or stepper motors. You can find a linear motor in a maglev (Transrapid) train, where the train "flies" on the ground.

Nano Engine

Built nanomotor at UC Berkeley. The engine is 500 nm by 300 times smaller than the diameter of a human hair

Researchers at University of California, Berkeley, have developed rotational bearings based on carbon nanotubes, multiwall. By connecting a gold plate (with dimensions of 100 nm order) the outer layer of a suspension of multiwall carbon nanotubes (such as nested

carbon cylinders), are able to electrostatically rotate the cover abroad in connection with the inner core. These bearings are very robust; devices have oscillated thousands of times without any indication of wear. The work was done in situ one SEM. These nanoelectromechanical systems (NEMS) are the next step in miniaturization that may find its way into commercial aspects in the future.
Warning: thin vertical line seen in the middle, is the nanotube is attached to the rotor. When the outer tube is sheared, the rotor can rotate freely on the bearing of nanotubes.

About the Author

Assistant professor in lord venkateswara engineering college.I am doing phd in sathyabama university, Tamil Nadu,India.