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108-409: A brushless DC electric motor ( BLDC ), also known as an electronically commutated motor , is a synchronous motor using a direct current (DC) electric power supply. It uses an electronic controller to switch DC currents to the motor windings producing magnetic fields that effectively rotate in space and which the permanent magnet rotor follows. The controller adjusts the phase and amplitude of

216-436: A coil of wire wound around an iron core. DC running through the wire winding creates the magnetic field , providing the power that runs the motor. The misalignment generates a torque that tries to realign the fields. As the rotor moves, and the fields come into alignment, it is necessary to move either the rotor's or stator's field to maintain the misalignment and continue to generate torque and movement. The device that moves

324-415: A gland ) that covers the inside and outside edges of the bearing race to keep the grease from escaping. Bearings may also be packed with other materials. Historically, the wheels on railroad cars used sleeve bearings packed with waste or loose scraps of cotton or wool fiber soaked in oil, then later used solid pads of cotton. Bearings can be lubricated by a ring oiler , a metal ring that rides loosely on

432-422: A microcontroller , or may alternatively be implemented using analog or digital circuits. Commutation with electronics instead of brushes allows for greater flexibility and capabilities not available with brushed DC motors, including speed limiting, microstepping operation for slow and fine motion control, and a holding torque when stationary. Controller software can be customized to the specific motor being used in

540-703: A plain bearing ; this underlies speculation that cultures such as the Ancient Egyptians used roller bearings in the form of tree trunks under sleds. There is no evidence for this sequence of technological development. The Egyptians' own drawings in the tomb of Djehutihotep show the process of moving massive stone blocks on sledges as using liquid-lubricated runners which would constitute plain bearings. There are also Egyptian drawings of plain bearings used with hand drills . Wheeled vehicles using plain bearings emerged between about 5000 BC and 3000 BC . A recovered example of an early rolling-element bearing

648-408: A shaded-pole type. Costs are an important parameter for starters. Rotor excitation is a possible way to resolve the issue. In addition, starting methods for large synchronous machines include repetitive polarity inversion of the rotor poles during startup. By varying the excitation of a synchronous motor, it can be made to operate at lagging, leading and unity power factor . Excitation at which

756-435: A bearing into a bore or onto a shaft, it's important to keep the housing bore and shaft outer diameter to very close limits, which can involve one or more counterboring operations, several facing operations, and drilling, tapping, and threading operations. Alternatively, an interference fit can also be achieved with the addition of a tolerance ring . The service life of the bearing is affected by many factors not controlled by

864-438: A company to produce his innovation. Over a century, the company grew to make bearings of all types, including specialty steel bearings and an array of related products and services. Erich Franke invented and patented the wire race bearing in 1934. His focus was on a bearing design with a cross-section as small as possible and which could be integrated into the enclosing design. After World War II, he founded with Gerhard Heydrich

972-441: A decline in use of brushed motors. These disadvantages are: During the last hundred years, high-power DC brushed motors, once the mainstay of industry, were replaced by alternating current (AC) synchronous motors . Today, brushed motors are used only in low-power applications or where only DC is available, but the above drawbacks limit their use even in these applications. In brushless DC motors, an electronic controller replaces

1080-423: A different principle: The following table summarizes the notable characteristics of each of these bearing types. Reducing friction in bearings is often important for efficiency, to reduce wear and to facilitate extended use at high speeds and to avoid overheating and premature failure of the bearing. Essentially, a bearing can reduce friction by virtue of its shape, by its material, or by introducing and containing

1188-439: A direct-drive design. Brushed DC motors were invented in the 20th century and are still common. Brushless DC motors were made possible by the development of solid state electronics in the 1960s. An electric motor develops torque by keeping the magnetic fields of the rotor (the rotating part of the machine) and the stator (the fixed part of the machine) misaligned. One or both sets of magnets are electromagnets , made of

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1296-706: A discrete device); or it may be a layer of bearing metal either fused to the substrate (semi-discrete) or in the form of a separable sleeve (discrete). With suitable lubrication, plain bearings often give acceptable accuracy, life, and friction at minimal cost. Therefore, they are very widely used. However, there are many applications where a more suitable bearing can improve efficiency, accuracy, service intervals, reliability, speed of operation, size, weight, and costs of purchasing and operating machinery. Thus, many types of bearings have varying shapes, materials, lubrication, principle of operation, and so on. There are at least 6 common types of bearing, each of which operates on

1404-401: A drive system can operate at exactly the same speed. The power supply frequency determines motor operating speed. Hysteresis motors have a solid, smooth, cylindrical rotor, cast of a high coercivity magnetically "hard" cobalt steel. This material has a wide hysteresis loop (high coercivity ), meaning once it is magnetized in a given direction, it requires a high magnetic field to reverse

1512-682: A fixed armature , eliminating problems associated with connecting current to the moving armature. An electronic controller replaces the commutator assembly of the brushed DC motor, which continually switches the phase to the windings to keep the motor turning. The controller performs similar timed power distribution by using a solid-state circuit rather than the commutator system. Brushless motors offer several advantages over brushed DC motors, including high torque to weight ratio, increased efficiency producing more torque per watt , increased reliability, reduced noise, longer lifetime by eliminating brush and commutator erosion, elimination of ionizing sparks from

1620-490: A fluid between surfaces or by separating the surfaces with an electromagnetic field. Combinations of these can even be employed within the same bearing. An example is where the cage is made of plastic, and it separates the rollers/balls, which reduce friction by their shape and finish. Bearing design varies depending on the size and directions of the forces required to support. Forces can be predominately radial , axial ( thrust bearings ), or bending moments perpendicular to

1728-476: A great amount of power to RC racers and, if paired with appropriate gearing and high-discharge lithium polymer (Li-Po) or lithium iron phosphate (LiFePO4) batteries, these cars can achieve speeds over 160 kilometres per hour (99 mph). Brushless motors are capable of producing more torque and have a faster peak rotational speed compared to nitro- or gasoline-powered engines. Nitro engines peak at around 46,800 r/min and 2.2 kilowatts (3.0 hp), while

1836-464: A groove in the axle assembly. Bearings played a pivotal role in the nascent Industrial Revolution , allowing the new industrial machinery to operate efficiently. For example, they were used for holding wheel and axle assemblies to greatly reduce friction compared to prior non-bearing designs. The first patent for a radial-style ball bearing was awarded to Jules Suriray , a Parisian bicycle mechanic, on 3 August 1869. The bearings were then fitted to

1944-401: A hole. Lubrication is used to reduce friction. Lubricants come in different forms, including liquids, solids, and gases. The choice of lubricant depends on the specific application and factors such as temperature, load, and speed. In the ball bearing and roller bearing , to reduce sliding friction, rolling elements such as rollers or balls with a circular cross-section are located between

2052-476: A laminated metal backing. The PTFE liner offers consistent, controlled friction as well as durability, whilst the metal backing ensures the composite bearing is robust and capable of withstanding high loads and stresses throughout its long life. Its design also makes it lightweight-one tenth the weight of a traditional rolling element bearing. There are many methods of mounting bearings, usually involving an interference fit . When press fitting or shrink fitting

2160-433: A motor controller excites the coil windings in the actuator causing an interaction of the magnetic fields resulting in linear motion. Tubular linear motors are another form of linear motor design operated in a similar way. Brushless motors have become a popular motor choice for model aircraft including helicopters and drones . Their favorable power-to-weight ratios and wide range of available sizes have revolutionized

2268-461: A motor without losing its synchronism is called steady state stability limit of a synchronous motor. Synchronous motors are especially useful in applications requiring precise speed or position control: Bearing (mechanical) A bearing is a machine element that constrains relative motion to only the desired motion and reduces friction between moving parts . The design of the bearing may, for example, provide for free linear movement of

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2376-410: A net lagging power factor, the presence of overexcited synchronous motors moves the system's net power factor closer to unity, improving efficiency. Such power-factor correction is usually a side effect of motors already present in the system to provide mechanical work, although motors can be run without mechanical load simply to provide power-factor correction. In large industrial plants such as factories

2484-1078: A rotating component. Examples include ultra high-speed bearings in dental drills, aerospace bearings in the Mars Rover, gearbox and wheel bearings on automobiles, flexure bearings in optical alignment systems, and air bearings used in coordinate-measuring machines . Common motions permitted by bearings are: The first plain and rolling-element bearings were wood , closely followed by bronze . Over their history, bearings have been made of many materials, including ceramic , sapphire , glass , steel , bronze , and other metals. Plastic bearings made of nylon , polyoxymethylene , polytetrafluoroethylene , and UHMWPE , among other materials, are also in use today. Case Hardening Steel SAE 4118 High Alloy Steel M50NiL Watchmakers produce "jeweled" watches using sapphire plain bearings to reduce friction, thus allowing more precise timekeeping. Even basic materials can have impressive durability. Wooden bearings, for instance, can still be seen today in old clocks or in water mills where

2592-448: A separate source or from a generator directly connected to the motor shaft. A permanent magnet synchronous motor and reluctance motor requires a control system for operating ( VFD or servo drive ). There is a large number of control methods for synchronous machines, selected depending on the construction of the electric motor and the scope. Control methods can be divided into: The PMSMs can also operate on open-loop control, which

2700-428: A smaller brushless motor can reach 50,000 r/min and 3.7 kilowatts (5.0 hp). Larger brushless RC motors can reach upwards of 10 kilowatts (13 hp) and 28,000 r/min to power one-fifth-scale models. Synchronous motor Synchronous and induction motors are the most widely used AC motors. Synchronous motors rotate at a rate locked to the line frequency since they do not rely on induction to produce

2808-413: A solid steel cast rotor with projecting (salient) toothed poles. Typically there are fewer rotor than stator poles to minimize torque ripple and to prevent the poles from all aligning simultaneously—a position that cannot generate torque. The size of the air gap in the magnetic circuit and thus the reluctance is minimum when the poles align with the stator's (rotating) magnetic field, and increases with

2916-436: A squirrel cage in the rotor for starting—these are known as line-start or self-starting. These are typically used as higher-efficiency replacements for induction motors (owing to the lack of slip), but must ensure that synchronous speed is reached and that the system can withstand torque ripple during starting. PMSMs are typically controlled using direct torque control and field oriented control . Reluctance motors have

3024-447: A stationary armature and rotating field winding. This type of construction has an advantage over DC motor type where the armature used is of rotating type. Electric motors generate power due to the interaction of the magnetic fields of the stator and the rotor. In synchronous motors, the stator carries 3 phase currents and produces 3 phase rotating magnetic flux (and therefore a rotating magnetic field). The rotor eventually locks in with

3132-457: A synchronous machine shows armature current as a function of field current. With increasing field current armature current at first decreases, then reaches a minimum, then increases. The minimum point is also the point at which power factor is unity. This ability to selectively control power factor can be exploited for power factor correction of the power system to which the motor is connected. Since most power systems of any significant size have

3240-484: A type of linear motion bearing consisting of both an external and internal 90-degree vee angle. In the early 1980s, Pacific Bearing's founder, Robert Schroeder, invented the first bi-material plain bearing that was interchangeable with linear ball bearings. This bearing had a metal shell (aluminum, steel or stainless steel) and a layer of Teflon-based material connected by a thin adhesive layer. Today's ball and roller bearings are used in many applications, which include

3348-684: A variable speed response, brushless motors operate in an electromechanical system that includes an electronic motor controller and a rotor position feedback sensor. Brushless DC motors are widely used as servomotors for machine tool servo drives. Servomotors are used for mechanical displacement, positioning or precision motion control. DC stepper motors can also be used as servomotors; however, since they are operated with open loop control , they typically exhibit torque pulsations. Brushless motors are used in industrial positioning and actuation applications. For assembly robots, Brushless technogy may be used to build linear motors . The advantage of linear motors

Brushless DC electric motor - Misplaced Pages Continue

3456-446: A world-leading center for ball bearing production. The modern, self-aligning design of ball bearing is attributed to Sven Wingquist of the SKF ball-bearing manufacturer in 1907 when he was awarded Swedish patent No. 25406 on its design. Henry Timken , a 19th-century visionary and innovator in carriage manufacturing, patented the tapered roller bearing in 1898. The following year he formed

3564-461: Is a trend in the heating, ventilation, and air conditioning (HVAC) and refrigeration industries to use brushless motors instead of various types of AC motors . The most significant reason to switch to a brushless motor is a reduction in power required to operate them versus a typical AC motor. In addition to the brushless motor's higher efficiency, HVAC systems, especially those featuring variable-speed or load modulation, use brushless motors to give

3672-553: Is a wooden ball bearing supporting a rotating table from the remains of the Roman Nemi ships in Lake Nemi , Italy . The wrecks were dated to 40 BC. Leonardo da Vinci incorporated drawings of ball bearings in his design for a helicopter around the year 1500; this is the first recorded use of bearings in an aerospace design. However, Agostino Ramelli is the first to have published roller and thrust bearings sketches. An issue with

3780-646: Is another reason for their popularity. Legal restrictions for the use of combustion engine driven model aircraft in some countries, most often due to potential for noise pollution —even with purpose-designed mufflers for almost all model engines being available over the most recent decades—have also supported the shift to high-power electric systems. Their popularity has also risen in the radio-controlled (RC) car area. Brushless motors have been legal in North American RC car racing in accordance with Radio Operated Auto Racing (ROAR) since 2006. These motors provide

3888-414: Is applied at each of the connections. The wye ( Y -shaped) configuration, sometimes called a star winding, connects all of the windings to a central point, and power is applied to the remaining end of each winding. A motor with windings in delta configuration gives low torque at low speed but can give higher top speed. Wye configuration gives high torque at low speed, but not as high top speed. The wye winding

3996-435: Is commonly used in large and complex internal combustion engines in parts of the engine where directly splashed oil cannot reach, such as up into overhead valve assemblies. High-speed turbochargers also typically require a pressurized oil system to cool the bearings and keep them from burning up due to the heat from the turbine. Composite bearings are designed with a self-lubricating polytetrafluorethylene (PTFE) liner with

4104-410: Is derived from the verb " to bear "; a bearing being a machine element that allows one part to bear (i.e., to support) another. The simplest bearings are bearing surfaces , cut or formed into a part, with varying degrees of control over the form, size, roughness , and location of the surface. Other bearings are separate devices installed into a machine or machine part. The most sophisticated bearings for

4212-422: Is determined by load, temperature, maintenance, lubrication, material defects, contamination, handling, installation and other factors. These factors can all have a significant effect on bearing life. For example, the service life of bearings in one application was extended dramatically by changing how the bearings were stored before installation and use, as vibrations during storage caused lubricant failure even when

4320-439: Is due to the strain of the ball and race. With fluid bearings, it is due to how the pressure of the fluid varies with the gap (when correctly loaded, fluid bearings are typically stiffer than rolling element bearings). Some bearings use a thick grease for lubrication, which is pushed into the gaps between the bearing surfaces, also known as packing . The grease is held in place by a plastic, leather, or rubber gasket (also called

4428-411: Is greatest in the no-load and low-load regions of the motor's performance curve. Environments and requirements in which manufacturers use brushless-type DC motors include maintenance-free operation, high speeds, and operation where sparking is hazardous (i.e. explosive environments) or could affect electronically sensitive equipment. The construction of a brushless motor resembles a stepper motor , but

Brushless DC electric motor - Misplaced Pages Continue

4536-498: Is in operation, the speed of the motor is dependent only on the supply frequency. When the motor load is increased beyond the breakdown load, the motor falls out of synchronization and the rotor no longer follows the rotating magnetic field. Since the motor cannot produce torque if it falls out of synchronization, practical synchronous motors have a partial or complete squirrel-cage damper called an amortisseur winding to stabilize operation and facilitate starting. Because this winding

4644-488: Is limited only by the lifetime of their bearings . Brushed DC motors develop a maximum torque when stationary, linearly decreasing as velocity increases. Some limitations of brushed motors can be overcome by brushless motors; they include higher efficiency and lower susceptibility to mechanical wear. These benefits come at the cost of potentially less rugged, more complex, and more expensive control electronics. A typical brushless motor has permanent magnets that rotate around

4752-406: Is normally more efficient. Delta-connected windings can allow high-frequency parasitic electrical currents to circulate entirely within the motor. A Wye-connected winding does not contain a closed loop in which parasitic currents can flow, preventing such losses. Aside from the higher impedance of the wye configuration, from a controller standpoint, the two winding configurations can be treated exactly

4860-417: Is operating at an AC supply frequency of 60 Hz. The number of pole-pairs is 6, so the synchronous speed is: The number of magnetic poles, p {\displaystyle p} , is equal to the number of coil groups per phase. To determine the number of coil groups per phase in a 3-phase motor, count the number of coils, divide by the number of phases, which is 3. The coils may span several slots in

4968-408: Is similar to that of a synchronous alternator . The stator frame contains wrapper plate (except for wound-rotor synchronous doubly fed electric machines ). Circumferential ribs and keybars are attached to the wrapper plate. To carry the weight of the machine, frame mounts and footings are required. The synchronous stator winding consists of a 3 phase winding. It is provided with a 3 phase supply, and

5076-420: Is smaller than that of an equivalent induction motor and can overheat on long operation, and because large slip-frequency voltages are induced in the rotor excitation winding, synchronous motor protection devices sense this condition and interrupt the power supply (out of step protection). Above a certain size, synchronous motors cannot self-start. This property is due to rotor inertia; it cannot instantly follow

5184-462: Is sometimes used for start-up thus enabling the position sensing operation. The synchronous speed of a synchronous motor is given: in RPM , by: and in rad·s , by: where: A single-phase , 4-pole (2-pole-pair) synchronous motor is operating at an AC supply frequency of 50 Hz. The number of pole-pairs is 2, so the synchronous speed is: A three-phase , 12-pole (6-pole-pair) synchronous motor

5292-621: Is surrounded by the rotor), inrunners (the rotor is surrounded by the stator), or axial (the rotor and stator are flat and parallel). The advantages of a brushless motor over brushed motors are high power-to-weight ratio, high speed, nearly instantaneous control of speed (rpm) and torque, high efficiency, and low maintenance. Brushless motors find applications in such places as computer peripherals (disk drives, printers), hand-held power tools, and vehicles ranging from model aircraft to automobiles. In modern washing machines, brushless DC motors have allowed replacement of rubber belts and gearboxes by

5400-475: Is that they can produce linear motion without the need of a transmission system, such as ballscrews , leadscrew , rack-and-pinion , cam , gears or belts, that would be necessary for rotary motors. Transmission systems are known to introduce less responsiveness and reduced accuracy. Direct drive, brushless DC linear motors consist of a slotted stator with magnetic teeth and a moving actuator, which has permanent magnets and coil windings. To obtain linear motion,

5508-421: The magnetic circuit of these machines needs to be able to concentrate the magnetic flux, typically leading to the use of spoke type rotors. Machines that use ferrite magnets have lower power density and torque density when compared with neodymium machines. PMSMs have been used as gearless elevator motors since 2000. Most PMSMs require a variable-frequency drive to start them. However, some incorporate

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5616-399: The power line frequency , which is carefully controlled in large interconnected grid systems. Synchronous motors are available in self-excited, fractional to industrial sizes. In the fractional power range, most synchronous motors are used to provide precise constant speed. These machines are commonly used in analog electric clocks, timers and related devices. In typical industrial sizes,

5724-437: The angle between them. This creates torque that pulls the rotor into alignment with the nearest pole of the stator field. At synchronous speed the rotor is thus "locked" to the rotating stator field. This cannot start the motor, so the rotor poles usually have squirrel-cage windings embedded in them, to provide torque below synchronous speed. The machine thus starts as an induction motor until it approaches synchronous speed, when

5832-463: The application, resulting in greater commutation efficiency. The maximum power that can be applied to a brushless motor is limited almost exclusively by heat; too much heat weakens the magnets and damages the windings' insulation. When converting electricity into mechanical power, brushless motors are more efficient than brushed motors primarily due to the absence of brushes, which reduces mechanical energy loss due to friction. The enhanced efficiency

5940-423: The applied load changes. One source of motion is gaps or "play" in the bearing. For example, a 10 mm shaft in a 12 mm hole has 2 mm play. Allowable play varies greatly depending on the use. As an example, a wheelbarrow wheel supports radial and axial loads. Axial loads may be hundreds of newtons force left or right, and it is typically acceptable for the wheel to wobble by as much as 10 mm under

6048-440: The ball and roller bearings is that the balls or rollers rub against each other, causing additional friction. This can be reduced by enclosing each individual ball or roller within a cage. The captured, or caged, ball bearing was originally described by Galileo in the 17th century. The first practical caged-roller bearing was invented in the mid-1740s by horologist John Harrison for his H3 marine timekeeper. In this timepiece,

6156-521: The bearing manufacturers. For example, bearing mounting, temperature, exposure to external environment, lubricant cleanliness, and electrical currents through bearings . High frequency PWM inverters can induce electric currents in a bearing, which can be suppressed by the use of ferrite chokes . The temperature and terrain of the micro-surface will determine the amount of friction by touching solid parts. Certain elements and fields reduce friction while increasing speeds. Strength and mobility help determine

6264-446: The bearing. A second source of motion is elasticity in the bearing itself. For example, the balls in a ball bearing are like stiff rubber and under load deform from a round to a slightly flattened shape. The race is also elastic and develops a slight dent where the ball presses on it. The stiffness of a bearing is how the distance between the parts separated by the bearing varies with the applied load. With rolling element bearings, this

6372-421: The bottom, with gears partially immersed in the liquid, or crank rods that can swing down into the pool as the device operates. The spinning wheels fling oil into the air around them, while the crank rods slap at the surface of the oil, splashing it randomly on the engine's interior surfaces. Some small internal combustion engines specifically contain special plastic flinger wheels which randomly scatter oil around

6480-461: The brush commutator contacts. An electronic sensor detects the angle of the rotor and controls semiconductor switches such as transistors that switch current through the windings, either reversing the direction of the current or, in some motors turning it off, at the correct angle so the electromagnets create torque in one direction. The elimination of the sliding contact allows brushless motors to have less friction and longer life; their working life

6588-1005: The built-in microprocessor continuous control over cooling and airflow. The application of brushless DC motors within industrial engineering primarily focuses on manufacturing engineering or industrial automation design. Brushless motors are ideally suited for manufacturing applications because of their high power density, good speed-torque characteristics, high efficiency, wide speed ranges and low maintenance. The most common uses of brushless DC motors in industrial engineering are motion control , linear actuators , servomotors , actuators for industrial robots, extruder drive motors and feed drives for CNC machine tools. Brushless motors are commonly used as pump, fan and spindle drives in adjustable or variable speed applications as they are capable of developing high torque with good speed response. In addition, they can be easily automated for remote control. Due to their construction, they have good thermal characteristics and high energy efficiency . To obtain

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6696-456: The caged bearing was only used for a very limited oscillating motion, but later on, Harrison applied a similar bearing design with a true rotational movement in a contemporaneous regulator clock. The first patent on ball bearings was awarded to Philip Vaughan , a British inventor and ironmaster in Carmarthen in 1794. His was the first modern ball-bearing design, with the ball running along

6804-408: The central rotating shaft of the bearing. The ring hangs down into a chamber containing lubricating oil. As the bearing rotates, viscous adhesion draws oil up the ring and onto the shaft, where the oil migrates into the bearing to lubricate it. Excess oil is flung off and collects in the pool again. A rudimentary form of lubrication is splash lubrication . Some machines contain a pool of lubricant in

6912-485: The commutator, and an overall reduction of electromagnetic interference (EMI). With no windings on the rotor, they are not subjected to centrifugal forces, and because the windings are supported by the housing, they can be cooled by conduction, requiring no airflow inside the motor for cooling. This in turn means that the motor's internals can be entirely enclosed and protected from dirt or other foreign matter. Brushless motor commutation can be implemented in software using

7020-450: The commutator, making sliding electrical contact with successive segments as the rotor turns. The brushes selectively provide electric current to the windings. As the rotor rotates, the commutator selects different windings and the directional current is applied to a given winding such that the rotor's magnetic field remains misaligned with the stator and creates a torque in one direction. The brush commutator has disadvantages that has led to

7128-445: The company Franke & Heydrich KG (today Franke GmbH) to push the development and production of wire race bearings. Richard Stribeck's extensive research on ball bearing steels identified the metallurgy of the commonly used 100Cr6 (AISI 52100), showing coefficient of friction as a function of pressure. Designed in 1968 and later patented in 1972, Bishop-Wisecarver's co-founder Bud Wisecarver created vee groove bearing guide wheels,

7236-427: The controller implements the traditional brushes' functionality, it needs to know the rotor's orientation relative to the stator coils. This is automatic in a brushed motor due to the fixed geometry of the rotor shaft and brushes. Some designs use Hall effect sensors or a rotary encoder to directly measure the rotor's position. Others measure the back-EMF in the undriven coils to infer the rotor position, eliminating

7344-454: The conventional inrunner configuration, the permanent magnets are part of the rotor. Three stator windings surround the rotor. In the external-rotor outrunner configuration, the radial relationship between the coils and magnets is reversed; the stator coils form the center (core) of the motor, while the permanent magnets spin within an overhanging rotor that surrounds the core. Outrunners typically have more poles, set up in triplets to maintain

7452-451: The current pulses that control the speed and torque of the motor. It is an improvement on the mechanical commutator (brushes) used in many conventional electric motors. The construction of a brushless motor system is typically similar to a permanent magnet synchronous motor (PMSM), but can also be a switched reluctance motor , or an induction (asynchronous) motor . They may also use neodymium magnets and be outrunners (the stator

7560-432: The duration by which ten percent of the bearings in that application can be expected to have failed due to classical fatigue failure (and not any other mode of failure such as lubrication starvation, wrong mounting etc.), or, alternatively, the duration at which ninety percent will still be operating. The L10/B10 life of the bearing is theoretical, and may not represent service life of the bearing. Bearings are also rated using

7668-443: The fields based on the position of the rotor is called a commutator . In brushed motors this is done with a rotary switch on the motor's shaft called a commutator. It consists of a rotating cylinder or disc divided into multiple metal contact segments on the rotor. The segments are connected to conductor windings on the rotor. Two or more stationary contacts called brushes , made of a soft conductor such as graphite , press against

7776-568: The increased efficiency of the motor leads to longer periods of use before the battery needs to be charged. Low speed, low power brushless motors are used in direct-drive turntables for gramophone records . Brushless motors can also be found in marine applications, such as underwater thrusters . Drones also utilize brushless motors to elevate their performance . Brushless motors are found in electric vehicles , hybrid vehicles , personal transporters , and electric aircraft . Most electric bicycles use brushless motors that are sometimes built into

7884-528: The interaction between synchronous motors and other, lagging, loads may be an explicit consideration in the plant's electrical design. where, here, When load is applied, torque angle δ {\displaystyle \delta } increases. When δ {\displaystyle \delta } = 90° the torque will be maximum. If load is applied further then the motor will lose its synchronism, since motor torque will be less than load torque. The maximum load torque that can be applied to

7992-480: The interior of the mechanism. For high-speed and high-power machines, a loss of lubricant can result in rapid bearing heating and damage due to friction. Also, in dirty environments, the oil can become contaminated with dust or debris, increasing friction. In these applications, a fresh supply of lubricant can be continuously supplied to the bearing and all other contact surfaces, and the excess can be collected for filtration, cooling, and possibly reuse. Pressure oiling

8100-491: The load the bearing type can carry. Alignment factors can play a damaging role in wear and tear, yet overcome by computer aid signaling and non-rubbing bearing types, such as magnetic levitation or air field pressure. Fluid and magnetic bearings can have practically indefinite service lives. In practice, fluid bearings support high loads in hydroelectric plants that have been in nearly continuous service since about 1900 and show no signs of wear. Rolling element bearing life

8208-426: The magnetization. The rotating stator field causes each small volume of the rotor to experience a reversing magnetic field. Because of hysteresis the phase of the magnetization lags behind the phase of the applied field. Thus the axis of the magnetic field induced in the rotor lags behind the axis of the stator field by a constant angle δ, producing torque as the rotor tries to "catch up" with the stator field. As long as

8316-778: The main axis. Different bearing types have different operating speed limits. Speed is typically specified as maximum relative surface speeds, often specified ft/s or m/s. Rotational bearings typically describe performance in terms of the product DN where D is the mean diameter (often in mm) of the bearing and N is the rotation rate in revolutions per minute. Generally, there is considerable speed range overlap between bearing types. Plain bearings typically handle only lower speeds, rolling element bearings are faster, followed by fluid bearings and finally magnetic bearings which are limited ultimately by centripetal force overcoming material strength. Some applications apply bearing loads from varying directions and accept only limited play or "slop" as

8424-559: The market for electric-powered model flight, displacing virtually all brushed electric motors, except for low powered inexpensive often toy grade aircraft. They have also encouraged growth of simple, lightweight electric model aircraft, rather than the previous internal combustion engines powering larger and heavier models. The increased power-to-weight ratio of modern batteries and brushless motors allows models to ascend vertically, rather than climb gradually. The low noise and lack of mass compared to small glow fuel internal combustion engines

8532-418: The most demanding applications are very precise components; their manufacture requires some of the highest standards of current technology. Rotary bearings hold rotating components such as shafts or axles within mechanical systems and transfer axial and radial loads from the source of the load to the structure supporting it. The simplest form of bearing, the plain bearing , consists of a shaft rotating in

8640-420: The motor to run backwards briefly, adding even more complexity to the startup sequence. Other sensorless controllers are capable of measuring winding saturation caused by the position of the magnets to infer the rotor position. A typical controller contains three polarity-reversible outputs controlled by a logic circuit. Simple controllers employ comparators working from the orientation sensors to determine when

8748-406: The motors have important differences in implementation and operation. While stepper motors are frequently stopped with the rotor in a defined angular position, a brushless motor is usually intended to produce continuous rotation. Both motor types may have a rotor position sensor for internal feedback. Both a stepper motor and a well-designed brushless motor can hold finite torque at zero RPM. Because

8856-406: The moving part or for free rotation around a fixed axis ; or, it may prevent a motion by controlling the vectors of normal forces that bear on the moving parts. Most bearings facilitate the desired motion by minimizing friction. Bearings are classified broadly according to the type of operation, the motions allowed, or the directions of the loads (forces) applied to the parts. The term "bearing"

8964-422: The need for separate Hall effect sensors. These are therefore often called sensorless controllers. Controllers that sense rotor position based on back-EMF have extra challenges in initiating motion because no back-EMF is produced when the rotor is stationary. This is usually accomplished by beginning rotation from an arbitrary phase, and then skipping to the correct phase if it is found to be wrong. This can cause

9072-487: The only load on the bearing was its own weight; the resulting damage is often false brinelling . Bearing life is statistical: several samples of a given bearing will often exhibit a bell curve of service life, with a few samples showing significantly better or worse life. Bearing life varies because microscopic structure and contamination vary greatly even where macroscopically they seem identical. Bearings are often specified to give an "L10" (US) or "B10" (elsewhere) life,

9180-640: The output phase should be advanced. More advanced controllers employ a microcontroller to manage acceleration, control motor speed and fine-tune efficiency. Two key performance parameters of brushless DC motors are the motor constants K T {\displaystyle K_{T}} (torque constant) and K e {\displaystyle K_{e}} (back-EMF constant, also known as speed constant K V = 1 K e {\displaystyle K_{V}={1 \over K_{e}}} ). Brushless motors can be constructed in several different physical configurations. In

9288-453: The power factor is unity is termed normal excitation voltage . The magnitude of current at this excitation is minimum. Excitation voltage more than normal excitation is called over excitation voltage, excitation voltage less than normal excitation is called under excitation. When the motor is over excited, the back emf will be greater than the motor terminal voltage. This causes a demagnetizing effect due to armature reaction. The V curve of

9396-459: The power line frequency to run the gear mechanism at the correct speed. Such small synchronous motors are able to start without assistance if the moment of inertia of the rotor and its mechanical load are sufficiently small. The motor accelerates from slip speed to synchronous speed during an accelerating half cycle of the reluctance torque. Single-phase synchronous motors such as in electric wall clocks can freely rotate in either direction, unlike

9504-407: The races or journals of the bearing assembly. A wide variety of bearing designs exists to allow the demands of the application to be correctly met for maximum efficiency, reliability, durability, and performance. It is sometimes assumed that the invention of the rolling bearing, in the form of wooden rollers supporting– or bearing –an object being moved, predates the invention of a wheel rotating on

9612-413: The reluctance type, hysteresis motors are used where precise constant speed is required. Usually made in larger sizes (larger than about 1 horsepower or 1 kilowatt) these motors require direct current (DC) to excite (magnetize) the rotor. This is most straightforwardly supplied through slip rings . A brushless AC induction and rectifier arrangement can also be used. The power may be supplied from

9720-418: The resultant air-gap flux by the forward motion of the prime mover ". Motor action occurs if the field poles are "dragged behind the resultant air-gap flux by the retarding torque of a shaft load ". The two major types of synchronous motors are distinguished by how the rotor is magnetized: non-excited and direct-current excited. In non-excited motors, the rotor is made of steel. It rotates in step with

9828-405: The rotating magnetic field and rotates along with it. Once the rotor field locks in with the rotating magnetic field, the motor is said to be synched. A single-phase (or two-phase derived from single phase) stator is possible, but in this case the direction of rotation is not defined and the machine may start in either direction unless prevented from doing so by startup arrangements. Once the motor

9936-538: The rotating stator field. A major advantage of the hysteresis motor is that since the lag angle δ is independent of speed, it develops constant torque from startup to synchronous speed. Therefore, it is self-starting and doesn't need an induction winding to start it, although many designs embed a squirrel-cage conductive winding structure in the rotor to provide extra torque at start-up. Hysteresis motors are manufactured in sub-fractional horsepower ratings, primarily as servomotors and timing motors. More expensive than

10044-406: The rotation of the stator's magnetic field. Since a synchronous motor produces no inherent average torque at standstill, it cannot accelerate to synchronous speed without a supplemental mechanism. Large motors operating on commercial power include a squirrel-cage induction winding that provides sufficient torque for acceleration and also serves to damp motor speed oscillations. Once the rotor nears

10152-422: The rotor "pulls in" and locks to the stator field. Reluctance motor designs have ratings that range from fractional horsepower (a few watts) to about 22 kW . Small reluctance motors have low torque , and are generally used for instrumentation applications. Moderate torque, multi-horsepower motors use squirrel cage construction with toothed rotors. When used with an adjustable frequency power supply, all motors in

10260-420: The rotor is below synchronous speed, each particle of the rotor experiences a reversing magnetic field at the "slip" frequency that drives it around its hysteresis loop, causing the rotor field to lag and create torque. The rotor has a 2-pole low reluctance bar structure. As the rotor approaches synchronous speed and slip goes to zero, this magnetizes and aligns with the stator field, causing the rotor to "lock" to

10368-422: The rotor is provided with a DC supply. DC excited motors require brushes and slip rings to connect to the excitation supply. The field winding can be excited by a brushless exciter. Cylindrical, round rotors, (also known as non-salient pole rotor) are used for up to six poles. In some machines or when a large number of poles are needed, a salient pole rotor is used. Most synchronous motor construction uses

10476-491: The rotor to create a constant magnetic field. The stator carries windings connected to an AC electricity supply to produce a rotating magnetic field (as in an asynchronous motor ). At synchronous speed the rotor poles lock to the rotating magnetic field. PMSMs are similar to brushless DC motors . Neodymium magnets are the most common, although rapid fluctuation of neodymium magnet prices triggered research in ferrite magnets . Due to inherent characteristics of ferrite magnets ,

10584-463: The rotor's magnetic field. Induction motors require slip : the rotor must rotate at a frequency slightly slower than the AC alternations in order to induce current in the rotor. Small synchronous motors are used in timing applications such as in synchronous clocks , timers in appliances, tape recorders and precision servomechanisms in which the motor must operate at a precise speed; accuracy depends on

10692-499: The same. Brushless motors fulfill many functions originally performed by brushed DC motors, but cost and control complexity prevents brushless motors from replacing brushed motors completely in the lowest-cost areas. Nevertheless, brushless motors have come to dominate many applications, particularly devices such as computer hard drives and CD/DVD players. Small cooling fans in electronic equipment are powered exclusively by brushless motors. They can be found in cordless power tools where

10800-479: The stator core, making it tedious to count them. For a 3-phase motor, if you count a total of 12 coil groups, it has 4 magnetic poles. For a 12-pole 3-phase machine, there will be 36 coils. The number of magnetic poles in the rotor is equal to the number of magnetic poles in the stator. The principal components of electric motors are the stator and the rotor. Synchronous motor and induction motor stators are similar in construction. The construction of synchronous motor

10908-429: The stator's rotating magnetic field, so it has an almost-constant magnetic field through it. The external stator field magnetizes the rotor, inducing the magnetic poles needed to turn it. The rotor is made of a high- retentivity steel such as cobalt steel. These are manufactured in permanent magnet , reluctance and hysteresis designs: A permanent-magnet synchronous motor (PMSM) uses permanent magnets embedded in

11016-425: The synchronous motor provides an efficient means of converting AC energy to work ( electrical efficiency above 95% is normal for larger sizes) and it can operate at leading or unity power factor and thereby provide power-factor correction. Synchronous motors fall under the category of synchronous machines that also includes synchronous generators. Generator action occurs if the field poles are "driven ahead of

11124-451: The synchronous speed, the field winding becomes excited and the motor pulls into synchronization. Very large motor systems may include a "pony" motor that accelerates the unloaded synchronous machine before load is applied. Electronically controlled motors can be accelerated from zero speed by changing the frequency of the stator current. Small synchronous motors are commonly used in line-powered electric mechanical clocks or timers that use

11232-406: The three groups of windings, and have a higher torque at low RPMs. In the flat axial flux type , used where there are space or shape constraints, stator and rotor plates are mounted face to face. In all brushless motors, the coils are stationary. There are two common electrical winding configurations; the delta configuration connects three windings to each other in a triangle-like circuit, and power

11340-407: The varying load. In contrast, a lathe may position a cutting tool to ±0.002 mm using a ball lead screw held by rotating bearings. The bearings support axial loads of thousands of newtons in either direction and must hold the ball lead screw to ±0.002 mm across that range of loads Stiffness is the amount that the gap varies when the load on the bearing changes, distinct from the friction of

11448-413: The water provides cooling and lubrication. By far, the most common bearing is the plain bearing , a bearing that uses surfaces in rubbing contact, often with a lubricant such as oil or graphite. A plain bearing may or may not be a discrete device. It may be nothing more than the bearing surface of a hole with a shaft passing through it, or of a planar surface that bears another (in these cases, not

11556-657: The wheel hub itself, with the stator fixed solidly to the axle and the magnets attached to and rotating with the wheel. The same principle is applied in self-balancing scooter wheels. Most electrically powered radio-controlled models use brushless motors because of their high efficiency. Brushless motors are found in many modern cordless tools, including some string trimmers , leaf blowers , saws ( circular and reciprocating ), and drills / drivers . The weight and efficiency advantages of brushless over brushed motors are more important to handheld, battery-powered tools than to large, stationary tools plugged into an AC outlet. There

11664-461: The winning bicycle ridden by James Moore in the world's first bicycle road race, Paris-Rouen , in November 1869. In 1883, Friedrich Fischer , founder of FAG , developed an approach for milling and grinding balls of equal size and exact roundness by means of a suitable production machine, which set the stage for the creation of an independent bearing industry. His hometown Schweinfurt later became

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