Split Stator

An important difference between a universal and a split-phase motor is that the split-phase motor has…?

A. two brushes attached to the stator.
B. a single coil formed on the rotor.
C. two windings on the stator.
D. an armature with a commutator.

C. Two windings, one for starting and one for running.

Techical design performance of the traction machine

Rotating magnetic field as a vector sum magnetic from 3 phase coils.

An electric motor converts electrical energy into kinetic energy. The reverse task, to convert kinetic energy into electrical energy, is performed by a generator or dynamo. In many cases the two devices differ only in their application construction details and minor, and some applications use a single device to fill both roles. For example, the traction motors used on locomotives often perform 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 the wire and the magnetic field. Most magnetic motors are engines Rotary, linear, but there. 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 rotates because the wires and magnetic field are arranged so that a couple develops around the rotor shaft. The motor contains electromagnets that are wrapped in a frame. Despite this framework is often called the armature, that term is often erroneously applied. Correctly, the armature is the part of the engine through which blood is supplied input. Depending on the design of the machine, either the rotor or the stator can serve as armor.

DC motors

Electric motors of various sizes.

One of the first electromagnetic rotary motors 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 is passed through the cable, the cable goes around the magnet, showing that the current resulted in a circular magnetic field around the wire. This motor is often demonstrated in physics classes at the school, but (brine water) is sometimes used instead of toxic mercury. This is the most Simple Class of electric motors called homopolar motors. A further refinement is the wheel of Barlow.

Another early engine design used an alternative electric plunger inside a solenoid switching; concept that could be seen as an electromagnetic version of a two-stroke engine internal combustion.

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

The classic DC motor has a rotating armature in the form of an electromagnet. A switch called a rotary switch reverses the direction of the electric current twice every cycle, the flow through the armature, so that the poles of the electromagnet push and pull against the permanent magnets on the outside of the engine. Since the poles of the armature electromagnet pass the poles of permanent magnets, the switch reverses the polarity armature of the electromagnet. In that moment of change of polarity, inertia keeps the engine is classic in the right direction. (See diagram below.)

A simple DC motor power. When the coil is powered, a magnetic field generated around the armature. The left side of the armature away from the magnet attracted to the left and right, causing rotation.

The armature continues to rotate.

When the armature becomes horizontally aligned, the commutator reverses the direction of current through the coil, the magnetic field reversal. The process repeats.

Field wound DC motor

The permanent magnets in the stator outside () of a DC motor can be replaced by electromagnets. By varying the field current is possible to change the link speed / torque motor. Normally, the field winding will be placed in series (series wound) with the armature winding for high torque at low speed into the wound parallel (shunt) with the armor to get a high speed low torque engine, or have a settlement in part, in parallel, and partly in the series (composed of the wound) of a balance that gives a constant speed in a range of loads. Further reductions in the current field are possible to win even faster, but the pair proportionately smaller, so-called "weak field" operation.

Theory

If the axis of a DC motor is activated by an external force, the engine will behave like a generator and produce an electrical driving force (EMF). This tension is also generated during normal engine operation. The spinning motor produces a voltage known as back EMF, because he opposes the applied voltage the engine. Therefore, the voltage drop in an engine is the voltage drop due to back EMF and the voltage drop resulting from the parasitic resistance internal windings apperature's. The current through a motor is given by the following equation:

I = (Vapplied? Vbackemf) / Rapperature —

The mechanical energy produced by the motor is given by:

P = I * Vbackemf —

Since the emf is proportional the engine speed when an electric motor is first started or is completely stalled, there is zero back EMF. Therefore, the current through the apperature is much greater. This high current will produce a strong electric field to start the engine turning. As the motor turns, the increase of EMF back until it is equal 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, current and back EMF of an engine load:

Load = Vbackemf * I —

Vapplied = I * Rapperature? Vbackemf —

Vbackemf = speed * Fluxapperature —

Speed control

In general, the speed of rotation of a DC motor is proportional to the voltage applied to it, and the torque is proportional to current. Speed control can be achieved through battery outlets variable, the variable supply voltage, resistors or electronic controls. The address of a motor wound DC field can be changed by investing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors).
The effective stress can be modified by inserting a series resistor or by an electronically controlled switching device made of thyristors, transistors arc rectifiers, or, earlier, as mercury. In a circuit known as a helicopter, the average voltage applied to the motor is varied by changing the voltage very quickly. As the "on" to "off" relationship (duty cycle) is varied to alter the average applied voltage, engine speed varies. The percentage "on" time multiplied by the supply voltage provides the average voltage applied to the motor. Therefore, with a source of 100 V and 25% "in" Medium voltage while the engine is 25 V. During the 'off' time, the motor current flows through a diode called a flywheel diode. At this point in the cycle of current supply will be zero, and hence the motor current average is always greater than the current offer unless the percentage "on" time is 100%. 100% "on" time of supply and motor current are equal. The rapid switching wastes less energy than the resistances in series. Output filters smooth the average voltage applied to the motor and reduce motor noise. This method is also called pulse width modulation, or PWM, and it is often controlled by a microprocessor.

As the number of motors, DC motor develops its maximum torque at low speed, it is often used in traction applications such as electric locomotives, and trams. Another application is starter motors for diesel and small gasoline. No Series Motors be used in applications where the unit may fail (such as tape drives). As the engine accelerates, the armature (and hence field) current reduces. The reduction in field causes the engine to speed up (see the 'weak' in the previous section) until it destroys itself. This can also be a problem with railway motors in the event of a loss of adhesion since, unless quickly brought under control, The motors can reach speeds much higher than it would in normal circumstances. This can not only cause problems for themselves engines and fishing gear, but because of the speed differential between the rails and wheels can also cause severe damage to the rails and wheel treads, as 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 to weaken the resistance and the field, the electronic control controls the motor current and changes the field to weaken the resistance in the circuit when the motor current drops below a preset value (this is when the engine is at its full design speed). Once the resistance is in the motor circuit speed is increased above its normal speed at its rated voltage. When increases the motor current control is disconnected from the resilience and low-speed torque is available.

An interesting method of speed control of a motor DC is the Ward Leonard control. It is a method of controlling a DC motor (usually a shunt or compound wound) and was developed as a method of providing a motor speed-controlled AC power, though not without its advantages in DC systems. The AC supply is used to drive an AC motor, usually a motor induction that drives a DC generator or dynamo. The DC output of the armature is directly connected to the armature of the DC motor (usually construction identical). The shunt field windings of both DC machines are driven through a variable resistor of the generator armature. This variable resistance offers very good control of velocity standstill at full speed, and a consistent pair. This control method is the de facto method from its development until it was replaced by systems Solid state thyristor. We found service in almost any environment that requires good speed control, passenger lifts through to head large mine shafts, and even industrial process machinery and electric cranes. Its main disadvantage is that three teams are required to implement a scheme (five in very large installations, such as DC machines are often duplicated and controlled by a tandem variable resistor). In many applications, the motor-generator is often left permanently to avoid delays that would otherwise be caused by starting, as required. There are numerous legacy Ward-Leonard facilities still in service.

Universal motors

A variant of the engine wound field DC motor is universal. The name derives from the fact that you can use supply AC / DC, although in practice they are almost always used with AC supply. The principle is that an engine of the wound field DC current in the field and armor (and thus the resulting magnetic field) 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 meet the AC impedance (should be considered as pulsating force), and the resultant motor is generally less efficient than a pure DC motor equivalent. Operating at normal line frequency power, the maximum output of universal motors is limited and motors exceeding one kilowatt are rare. But universal motors also form the basis of the traditional railway traction motor. In this application, to maintain their high electrical efficiency, which were operated supplies low frequency AC of 25 Hz and 16 2 / 3 Hertz operation being common. Because they are the universal motors, locomotives using this design also commonly capable of operating from a third rail DC powered.

The advantage of the universal motor is that AC power supplies can be used in engines with the typical characteristics of DC motors, especially high starting torque and very compact, if you run High speed is used. The downside is the maintenance and problems caused by the short life of the collector. As a result of these motors are generally used in devices of CA, such as food mixers and power tools being used only intermittently. The continuous monitoring of the speed of a universal motor running on AC is very easy to perform using a thyristor circuit, while stepped speed control can be performed using multiple taps on the field coil. Mixers households that are advertised many speeds usually combine a field coil with several taps and a diode that can be inserted in series with the motor (causing the engine to run a half-wave DC at half RMS voltage of the AC power line).

Unlike AC motors, universal motors can easily exceed one revolution per cycle of the mains current. This makes them useful for appliances such as blenders, vacuum cleaners and hair dryers when it requires a high-speed operation. Vacuum Many weed trimmer engines and exceed 10,000 RPM Dremel and other similar miniature grinders often exceed 30,000 rpm. A theoretical universal motor operating without mechanical load speeding, which can damage it. In real life, although having different friction, armature "windage" and the burden of any fan built-in cooling all measures to prevent speeding.

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

The advantages of universal motor and alternating current distribution in fact the installation of a low frequency Current distribution of economic traction for some railway facilities. At sufficiently low frequencies, the engine performance is about the same that if the engine is operating on DC. Frequencies as low as 162 / 3 Hertz were used.

AC motors

In 1882, Nikola Tesla identified the principle of rotating magnetic field and pioneered the use of a rotating field of force to operate the machines. Exploded the principle to design a unique two-phase induction motor in 1883. In 1885, Galileo Ferraris independently researched the concept. In 1888, Ferrari released their research in a paper to the Royal Academy of Sciences of Turin.

Introduction of Tesla's motor from 1888 initiated what is known as the second revolution industry, making possible the generation and distribution systems of long distance power transmission system by alternating current, also the invention of Tesla (1888) [1]. Before the invention of the rotating magnetic field, motors operated by a driver who passes continuously through a magnetic field stationary (as in homopolar motors).

Tesla had suggested that a machine switches can be removed and the device might work in a field rotational 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

induction motor.

Stator power

Rotor energy

Total energy supplied

Power developed

10

90

90

900

50

50

100

2500

In the induction motor, the field and armature were ideally strengths field of equality and the field and armature cores were of equal size. The total energy supplied to operate the device equal to the sum of the energy expended in the armature and field coils. [3] The power developed in the functioning of 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. An effective system of commercial polyphase generation and long-range transport was designed by the Almeria Decker Mill Creek, No. 1 [5] in Redlands in California [6].

Components and types

A typical AC motor consists of two parts:
1. A fixed stator coils have not supplied with AC current to produce a magnetic field rotating, and;
2. An internal rotor connected to the output shaft which are given by the spin pair.

There are two basic types of DC motors alternate depending on the type of rotor used:

• The synchronous motor, which rotates exactly at the supply frequency or a submultiple supply frequency, and;
• The induction motor, which turns slightly slower, and usually (though not necessarily exclusively) takes the form of squirrel cage motor.

Phase induction motors AC

Three phase induction motors rated 1 hp AC (746 W) and 25 W with small engine, CD player, toys and CD / DVD drive head travel

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

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

Induction motors are the workhorses of industry and engines of 500 kW (670 hp force) in production occur in highly standardized frame sizes, 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 kW in output, piping to compressors and units of tunnel wind. There are two types of rotors used in induction motors.

Squirrel Cage rotors: Most common engines common alternative use squirrel cage rotor, which are found in virtually all domestic and light industrial alternating current motors. The squirrel cage is his name its shape – a ring at each end of the rotor, with bars connecting the rings running the length of the rotor. It is typically cast aluminum or copper poured between rolled products of iron of the rotor, and usually only sounds the end will be visible. The vast majority of the rotor currents will flow through the bars in place the highest resistance and usually varnished laminates. Very tensions high flows are typical in the bars and end rings, high efficiency motors often the use of molten copper in order to reduce the rotor resistance.

In operation, the squirrel cage motor can be considered as a transformer with a rotation secondary – where the rotor is not rotating 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 discharge to the synchronous speed is only consume power to maintain rotor speed against friction and resistance losses by increasing the mechanical load and electrical load will – The electrical load is inherently related to mechanical loading. This is similar to a transformer where the primary electrical load is related to the secondary electric charge.

For this reason, as an example, a blower motor squirrel cage can cause the lights in a dark house and starts, but not dim the lights when you remove your fanbelt (and therefore mechanical load). In addition, a stalled squirrel cage motor (overloaded or a jammed shaft) will consume current limited only by circuit resistance in her attempts to start. Unless something else limits the current (or turns it off completely) overheating and destruction the winding insulation is the likely result.

Virtually every washing machine, dishwasher, separate fan, record player, etc. uses a variant of a squirrel cage motor.

Rotor Winding: An alternative design, called the wound rotor, is used when speed is required variable. In this case, the rotor has the same number of poles on the stator and the coils are made of wire, connected to slip rings on the tree. Carbon brushes slip rings to connect an external controller as a variable resistor that allows changing the motor slip rate. In certain high-speed variable wound rotor power units, receipt of 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 way for variable speed control before the advent of compact power electronic devices. Investors transistor with a frequency converter can 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 when only a single stage of the network is available, but this is never used in home appliances have because it can cause electrical interference and because of the high power requirements.)

Several methods of starting a polyphase motor are used. When the great inrush current and torque can be high allow the engine can be started through the line, by applying full line voltage to the terminals. When necessary to limit the current starting boot (where the motor is large compared to short-circuit capacity of the supply), reduced voltage starting using series inductors, an autotransformer, thyristors, or other devices that are used. One technique sometimes used is the star from the delta, where the motor coils are initially connected to the acceleration load, then moved to Delta, when the load is up to high speed. This technique is more common in Europe than in North America. Transistorized units directly can vary the voltage applied, as required by the motor starting characteristics and the load.

This type of motor is becoming increasingly common in applications traction as the locomotives, which 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 relation:

Ns = 120F / p

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

Actual RPM for an induction motor will be lower than this calculated synchronous speed by an amount known as slip that increases the torque produced. No load speed will be very close to synchronous. When loaded, standard motors have between 2-3% slip, special motors may have up to 7% slip, and a class of motors known as torque motors are rated for operation at 100% slip (0 RPM / full stop).
The AC motor slip is calculated by:

S = (NS? Nr) / Ns

where
NR = rotational speed in revolutions per minute.
Slip S = Standard, 0 to 1.

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

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

Three-phase AC synchronous motors

If connections to the rotor windings of a three phase motor are taken out of the ring and fed a separate field current to create a constant 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 magnetic field produced by the polyphase electrical supply.

The synchronous motor can also be used as an alternator.

Nowadays, synchronous motors are frequently driven by transistorized variable-frequency drives. This greatly facilitates the problem of starting the massive rotor of a large synchronous motor. Also, please launched as induction motors using a squirrel cage winding that shares the common rotor: once the motor reaches synchronous speed, no current induced in the squirrel cage winding so it has little effect on the synchronous operation of the engine, besides stabilizing the engine speed load changes.

Synchronous motors are occasionally used as traction motors, the TGV may be the best known example of such use.

Two-phase AC servo motors
A typical two-phase AC servo motor has a squirrel cage rotor and a field consisting of two coils: 1) a constant voltage (AC) main winding, and 2) voltage control (AC) winding in quadrature with the primary winding to produce a magnetic field swivel. The electrical resistance of the rotor is made high intentionally so that the speed of the torque curve is fairly linear. Two-phase servo motors are inherently high speed, low torque devices, strongly oriented to the unit load.

Single-phase AC induction

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

A common single-phase motor is the shaded pole motor, which is used in devices requiring low torque, such as electric fans or small appliances. In this motor, small single turn copper "coil shading "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 flux through the coil (Lenz's law), thus moving the maximum field strength across the pole face on each cycle, thus producing the necessary rotation the magnetic field.

Another common single phase motor is the division of phase induction motor, 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 connection with a centrifugal switch.

In the split-phase motor, the start of the winding is designed with a greater resistance than the running winding. This creates an LR circuit which slightly changes the current phase at the beginning of settlement. When starting the engine, the start of the winding is connected to the source power through a set of spring contacts pressed by the centrifugal switch is not yet rotating. The starting winding is wound with fewer turns wire smaller than the main winding, so it has a smaller inductance (L) and increased resistance (R). The lower L / R creates a small gap, no more about 30 degrees between the flux due to liquidation and the main flow of the starting winding. The starting direction of rotation can be reversed only by exchange connections start of the liquidation in connection with the running winding.

The phase of the magnetic field at the beginning of the settlement moves phase of the power grid, enabling the creation of a moving magnetic field that starts the engine. Once the engine reaches operating near design speed, the centrifugal switch activates, opening the contacts and disconnecting the start of the liquidation of the power supply. Then the motor operates exclusively in the running winding. The starting winding must be disconnected, since it would increase the losses in the engine.

A capacitor start motor, starting capacitor is inserted in series with the start of the liquidation, the establishment of an LC circuit that is capable of a phase change is much higher (and therefore a pair of startup much higher). The capacitor naturally adds expense to such motors.

Another variation is the Permanent Split-Capacitor (PSC) motor (also known as a starting point of the capacitor and the runtime). This motor operates similarly to the capacitor start motor described above, but do not change from centrifuge and the second winding is permanently connected to the power supply. PSC motors are frequently used in air handling, fans and blowers and other cases where variable speed is desired. By changing taps on the running winding but keeping the load constant, the engine can be made to run at different speeds. Are also provided clearance 6 connections are available separately, a 3-phase motor can be converted into a capacitor start and run commoning motor by two of the windings and connecting the third via a capacitor to act as the start of liquidation.

Repulsion motors single-rotor wind phase AC motors that are similar to universal motors. In a repulsion motor, the armature brushes are shorted and not connected in series with the field. Several types of repulsion motors have been manufactured, but the repulsion-start induction run (RS-IR) has been used motor more often. The RS-IR motor has a centrifugal switch that shorts all segments of the collector for the engine operates as an induction motor, once has accelerated to full speed. IR RS-engines have been used to provide high starting torque per ampere under conditions of cold and poor regulation operating temperatures voltage source. Few repulsion motors of any kind are sold after 2006.

Single-phase AC synchronous motors

Small single-phase AC motors can also be designed with magnetized rotors (or variations on this idea). The rotors in these motors do not require any current induced so do not slip backward against the mains frequency. Instead, they spin in sync with the grid frequency. Due to its high accuracy rate, these engines are generally used to mechanical clocks, audio turntables, and tape drives, also formerly widely used in high precision instruments clock as strip-chart recorders or telescope drive mechanisms. The shaded pole synchronous motor is one version.

Because inertia makes it difficult to accelerate instantly arrested rotor synchronous speed, these motors normally require some special feature to start. Several designs use a small induction motor (which may share the same field coils and rotor as the synchronous motor) or a very light rotor with a dual mechanism sense (to ensure that the rotor begins in the direction "forward").

Torque motors

A torque motor is a specialized form of induction motor that can operate indefinitely in the position (locked-rotor turning) without damage. In this mode, the engine applying a constant torque load (hence the name). A common application of a torque motor would be the supply and take-coil motors in one 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 winch is powered 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 requiring additional mechanisms 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 nucleus iron with salient poles is controlled by a set of external magnets that are connected electronically. A stepper motor can also be regarded as a cross between a motor electric current and a solenoid. As each coil is activated in turn, the rotor is aligned with the magnetic field produced by the energy field winding. Unlike of a synchronous motor, in its application, the motor can not continuously rotate but "steps" from one place to another, such as field coils are energized and without current in sequence. Depending on the sequence, the rotor can rotate forward or backward.

Drivers of step motor power or completely simple completely deenergize the field windings, leading the rotor to "Cog" to a limited number of positions, more sophisticated drivers can proportionally control the power of the field windings which allows the rotor to position "between" the "gear" items and therefore rotate very well. Computer-controlled engines step by step is one of the most versatile forms of positioning systems, especially when part of a digital servo-controlled system.

Step Into The motors can rotate in a specific angle with ease, and hence stepper motors are used in computer disk drives, when high precision offered is necessary for the proper functioning of, for example, a hard drive or CD drive.

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. Thus, the machine could act as a machine of constant excitation direct current (dc machine separately excited).

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

Brushless DC motors

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

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

Halfway between regular DC motors and stepper motors is the realm of motor brushless DC. 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 detect the position of the rotor and associated drive electronics. The coils are activated, phase one after another, by the electronics of the disk as triggered by signals from Hall effect sensors. In effect, they act as three-phase synchronous motors containing its own unit of variable frequency electronic. A special kind of motor driver brushless DC using EMF Feedback through connections the main stage instead of Hall effect sensors to determine position and speed. These engines are widely used in electric radio controlled vehicles.

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

• Compared with the fans of AC shaded-pole motors, which are very efficient, running much colder than the equivalent AC motors. This operation is much improved life cool fan bearings.
• Without a switch to perform the engine life of a brushless DC can be significantly higher compared to a DC motor through the brushes and a switch. Commutation also tends to cause a lot of power and RF noise, without a switch or brushes, a brushless motor can be used in sensitive electrical devices such as audio equipment or computers.
• The same hall effect devices providing commutation can also provide a convenient tachometer signal for closed loop control (servo control) applications. In fans, the tachometer signal can used to derive a
• good fan "of the signal.
• The engine can be easily synchronized with an internal clock or external As for precise speed control.
• Brushed motors can not be used in the vacuum of space, because it will weld themselves into a position immovable.
  Modern range of DC motors, brushless power in a fraction of a watt to many kilowatts. Larger brushless motors up to about 100 kW grade used in electric vehicles. Also find significant use in high-performance electric model aircraft.

Coreless DC motors

Nothing in the design of any of the engines described above requires that the iron (steel) parts of the rotor actually rotate; torque is exerted only on the coils of electromagnets. Taking advantage of this fact is the DC motor without a nucleus, a specialized agency of brush type 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 cylinder filled with clearance inside the stator magnets, a basket surrounding the stator magnets, or a flat cake (possibly formed in printed circuit board) extends between the upper and lower stator magnets. The windings are typically stabilized by being impregnated with epoxy resins.

Due the rotor is much lighter in weight (mass) of a conventional rotor formed from copper coils of steel sheet, the rotor can accelerate much faster, often achieving a mechanical time constant of 1 ms. This is especially true if the use of coils of aluminum rather than the heavier copper. But because there is no metal in mass in the rotor to act as a heat sink, even small coreless motors must often be cooled by forced air.

These engines are commonly used to drive the capstan (s) and tape drives are still widely used in high performance servo control systems.

Engines linear

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

Linear motors are most commonly 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

Nanomotor built at the University of California at Berkeley. The engine is 500 nm through 300 times more smaller than the diameter of a human hair

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

carbon cylinders), are able to electrostatically rotate the outer shell in relation to the inner core. These bearings are very robust; Devices have thousands of times it has fluctuated with no indication of wear. The work was done in situ in a SEM. These nanoelectromechanical systems (NEMS) are the following step in miniaturization that may find its way into commercial aspects in the future.
Note: The thin vertical chain saw in the middle, the nanotube is attached to the rotor. When cutting the outer tube, 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.