Brushless DC motors also known as
electronically commutated motors (ECMs, EC motors) are electric motors powered by direct-current (DC) electricity and having electronic commutation systems, rather than mechanical
commutatorsA commutator is a rotary electrical switch in certain types of electric motors or electrical generators that periodically reverses the current direction between the rotor and the external circuit. In a motor, it applies power to the best location on the rotor, and in a generator, picks off power...
and
brushesA brush is a device which conducts current between stationary wires and moving parts, most commonly in a rotating shaft. Typical applications include electric motors, alternators and electric generators.-Etymology:...
. The current-to-torque and frequency-to-speed relationships of BLDC motors are linear.
BLDC motors may be described as stepper motors, with fixed permanent magnets and possibly more poles on the rotor than the
statorThe stator is the stationary part of a rotor system, found in an electric generator, electric motor and biological rotors.Depending on the configuration of a spinning electromotive device the stator may act as the field magnet, interacting with the armature to create motion, or it may act as the...
, or
reluctance motorA reluctance motor is a type of electric motor that induces non-permanent magnetic poles on the ferromagnetic rotor. Torque is generated through the phenomenon of magnetic reluctance.A reluctance motor, in its various incarnations, may be known as a:...
s. The latter may be without permanent magnets, just poles that are induced on the rotor then pulled into alignment by timed stator windings. However, the term
stepper motor tends to be used for motors that are designed specifically to be operated in a mode where they are frequently stopped with the rotor in a defined angular position; this page describes more general BLDC motor principles, though there is overlap.
Brushless versus Brushed motor
Brushed DC motors have been in commercial use since 1886.
[Frank Julian Sprague#Joining the emerging electrical industry][Electric motor#The first electric motors] BLDC motors, however, have only been commercially possible since 1962.
[http://www.powertecmotors.com/a0201el.pdf][T.G. Wilson, P.H. Trickey, "D.C. Machine. With Solid State Commutation", AIEE paper I. CP62-1372, Oct 7, 1962]
Limitations of brushed DC motors overcome by BLDC motors include lower efficiency and susceptibility of the commutator assembly to mechanical wear and consequent need for servicing, at the cost of potentially less rugged and more complex and expensive control electronics. BLDC motors develop maximum
torqueTorque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
when stationary and have linearly decreasing torque with increasing speed as shown in the adjacent figure.
A BLDC motor has permanent magnets which rotate and a fixed
armatureIn electrical engineering, an armature generally refers to one of the two principal electrical components of an electromechanical machine–generally in a motor or generator, but it may also mean the pole piece of a permanent magnet or electromagnet, or the moving iron part of a solenoid or relay....
, eliminating the problems of connecting current to the moving armature. An electronic controller replaces the brush/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 brush/commutator system.
BLDC motors offer several advantages over brushed DC motors, including more torque per weight, more torque per
wattThe watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
(increased efficiency), increased reliability, reduced noise, longer lifetime (no brush and commutator erosion), elimination of ionizing sparks from the commutator, and overall reduction of
electromagnetic interferenceElectromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
(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.
The maximum power that can be applied to a BLDC motor is exceptionally high, limited almost exclusively by heat, which can weaken the magnets. (Magnets demagnetize at high temperatures, the
Curie pointIn physics and materials science, the Curie temperature , or Curie point, is the temperature at which a ferromagnetic or a ferrimagnetic material becomes paramagnetic on heating; the effect is reversible. A magnet will lose its magnetism if heated above the Curie temperature...
, and for neodymium-iron-boron magnets this temperature is lower than for other types.) A BLDC motor's main disadvantage is higher cost, which arises from two issues. First, BLDC motors require complex
electronic speed controlAn electronic speed control or ESC is an electronic circuit with the purpose to vary an electric motor's speed, its direction and possibly also to act as a dynamic brake...
lers to run. Brushed DC motors can be regulated by a comparatively simple controller, such as a rheostat (variable resistor). However, this reduces efficiency because power is wasted in the rheostat. Second, some practical uses have not been well developed in the commercial sector. For example, in the Radio Control (RC) hobby arena, brushless motors are often hand-wound while brushed motors are usually machine-wound. (Nevertheless, see "Applications", below.)
BLDC motors are often more efficient at converting electricity into mechanical power than brushed DC motors. This improvement is largely due to the absence of electrical and friction losses due to brushes. The enhanced efficiency is greatest in the no-load and low-load region of the motor's performance curve. Under high mechanical loads, BLDC motors and high-quality brushed motors are comparable in efficiency.
AC induction motors require induction of magnetic field in the rotor by the rotating field of the stator; this results in the magnetic and electric fields being out of phase. The phase difference requires greater current and current losses to achieve power. BLDC motors are microprocessor-controlled to keep the stator current in phase with the permanent magnets of the rotor, requiring less current for the same effect and therefore resulting in greater efficiency.
In general, manufacturers use brush-type DC motors when low system cost is a priority but brushless motors to fulfill requirements such as maintenance-free operation, high speeds, and operation in explosive environments where sparking could be hazardous.
Controller implementations
Because the controller must direct the rotor rotation, the controller requires some means of determining the rotor's orientation/position (relative to the stator coils.) Some designs use
Hall effect sensorA Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications....
s or a
rotary encoderA rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to an analog or digital code. The output of incremental encoders provides information about the motion of the shaft which is typically further processed...
to directly measure the rotor's position. Others measure the back
EMFIn physics, electromotive force, emf , or electromotance refers to voltage generated by a battery or by the magnetic force according to Faraday's Law, which states that a time varying magnetic field will induce an electric current.It is important to note that the electromotive "force" is not a...
in the undriven coils to infer the rotor position, eliminating the need for separate Hall effect sensors, and therefore are often called
sensorless controllers. Like an AC motor, the voltage on the undriven coils is sinusoidal, but over an entire commutation the output appears trapezoidal because of the DC output of the controller.
The controller contains 3 bi-directional outputs to drive high-current DC power, which are controlled by a logic circuit. Simple controllers employ comparators to determine when the output phase should be advanced, while more advanced controllers employ a
microcontrollerA microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
to manage acceleration, control speed and fine-tune efficiency.
Controllers that sense rotor position based on back-EMF have extra challenges in initiating motion because no
back-EMFThe counter-electromotive force also known as back electromotive force is the voltage, or electromotive force, that pushes against the current which induces it. CEMF is caused by a changing electromagnetic field. It is the effect of Lenz's Law of electromagnetism...
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 the motor to run briefly backwards, 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.
The controller unit is often referred to as an "ESC", meaning
Electronic Speed ControllerAn electronic speed control or ESC is an electronic circuit with the purpose to vary an electric motor's speed, its direction and possibly also to act as a dynamic brake...
.
Variations in construction
BLDC motors can be constructed in several different physical configurations: In the 'conventional' (also known as '
inrunnerThe term inrunner refers to a type of brushless motor used in radio controlled models, especially in reference to their use in aircraft to differentiate them from outrunners....
') configuration, the permanent magnets are part of the rotor. Three stator windings surround the rotor. In the '
outrunnerThe term outrunner refers to a type of brushless motor primarily used in electrically propelled, radio-controlled model aircraft.This type of motor spins its outer shell around its windings, much like motors found in ordinary CD-ROM computer drives. In fact, CD-ROM motors are frequently rewound...
' (or external-rotor) 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 which surrounds the core. The flat type, used where there are space or shape limitations, uses stator and rotor plates, mounted face to face. Outrunners typically have more poles, set up in triplets to maintain the three groups of windings, and have a higher torque at low RPMs. In all BLDC motors, the coils are stationary.
There are also two electrical configurations having to do with how the wires from the windings are connected to each other (not their physical shape or location). The delta configuration connects the three windings to each other (series circuits) in a triangle-like circuit, and power 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 (parallel circuits) and power is applied to the remaining end of each winding.
A motor with windings in delta configuration gives low torque at low rpm, but can give higher top rpm. Wye configuration gives high torque at low rpm, but not as high top rpm.
[http://www.patentstorm.us/patents/6493924-description.html]
Although efficiency is greatly affected by the motor's construction, the wye winding is normally more efficient. In delta-connected windings, half voltage is applied across the windings adjacent to the undriven lead (compared to the winding directly between the driven leads), increasing resistive losses. In addition, 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.
From a controller standpoint, the two styles of windings are treated exactly the same, although some less expensive controllers are designed to read voltage from the common center of the wye winding.
See Also:Programmable Magnets
AC and DC power supplies
It's helpful to consider three types of motors:
- Direct current (DC) motor: DC applied to both the stator and the rotor (via brushes and commutator), or else a permanent magnet stator. A BLDC motor has switched DC fed to the stator, and a permanent magnet rotor.
- Synchronous (or stepping) motor (AC): AC in one, DC in the other (i.e., rotor or stator). If it has a permanent-magnet rotor, it is much like a BLDC motor.
- Induction motor (AC): AC in both stator and rotor (mentioned for completeness).
Although BLDC motors are practically identical to permanent magnet AC motors, the controller implementation is what makes them DC. While AC motors feed sinusoidal current simultaneously to each of the legs (with an equal phase distribution), DC controllers only approximate this by feeding full positive and negative voltage to two of the legs at a time. The major advantage of this is that both the logic controllers and battery power sources also operate on DC, such as in computers and electric cars. In addition, the approximated sine wave leaves one leg undriven at all times, allowing for back-EMF-based sensorless feedback.
Vector drives are DC controllers that take the extra step of converting back to AC for the motor; they are sophisticated inverters. The DC-to-AC conversion circuitry is usually expensive and less efficient, but these have the advantage of being able to run smoothly at very low speeds or completely stop (and provide torque) in a position not directly aligned with a pole. Motors used with a vector drive are typically called AC motors. When running at low speeds and under load, they don't cool themselves significantly; temperature rise has to be allowed for.
A motor can be optimized for AC (i.e. vector control) or it can be optimized for DC (i.e. block commutation). A motor which is optimized for block commutation will typically generate trapezoidal EMF. One can easily observe the shape of the EMF by connecting the motor wires (at least two of them) to an oscilloscope and then hand-cranking/spinning the shaft.
Another very important issue, at least for some applications like automotive vehicles, is the constant
power speed ratio of a motor (CPSR)CPSR may refer to:*Computer Professionals for Social Responsibility*Current Program Status Register, an ARM computer processor feature - see Jazelle - CPSR: Mode indication*Canadian Political Science Review*Constant Power Speed Ratio...
. The CPSR has direct impact on needed size of the inverter. Example: A motor with a high CPSR in a vehicle can deliver the desired power (e.g. 40 kW) from 3,000 rpm to 12,000 rpm, while using a 100 A inverter. A motor with low CPSR would need a 400 A inverter in order to do the same.
Stepping motors can also operate as AC synchronous motors (for instance, the Slo-Syn by Superior Electric), or the unusual battery-powered quartz-timed micropower clock that has a continuous-motion sweep second hand.
KM rating
"K
M" is the motor constant, it can be measured in Nm torque per square root of W resistive loss. K
M is sometimes called the "motor size constant". The motor constant is winding independent (as long as the same conductive material used for wires); e.g. winding a motor with 6 turns with 2 parallel wires instead of 12 turns single wire will double the K
v velocity constant, but the K
M remains unchanged.
K
M can be used for selecting the size of a motor to use in an application.
K
v can be used for selecting the winding to use in the motor.
Kv rating
"K
v" is the motor velocity constant, measured in RPM per volt (not to be confused with "kV," the abbreviation for "kilovolt")
. The K
v rating of a brushless motor is the ratio of the motor's unloaded RPM to the peak (not RMS) voltage on the wires connected to the coils (the "back-EMF"). For example, a 5,700 K
v motor, supplied with 11.1 V, will run at a nominal 63,270 rpm (=5700 * 11.1).
By
Lenz's lawLenz's law is a common way of understanding how electromagnetic circuits must always obey Newton's third law and The Law of Conservation of Energy...
, a running motor will create a back-EMF proportional to the RPM. Once a motor is spinning so fast that the back-EMF is equal to the battery voltage (also called DC line voltage), it is impossible for the ESCs to "speed up" that motor, even with no load.
Applications
BLDC motors fulfill many functions originally performed by brushed DC motors,
but cost and control complexity prevents BLDC motors from replacing brushed motors completely in the lowest-cost areas. Nevertheless,
BLDC motors have come to dominate many applications, particularly devices such as computer
hard drivesA hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
and CD/DVD players.
Small cooling fans in electronic equipment are powered exclusively by BLDC motors.
They can be found in cordless power tools where the increased efficiency of the motor leads to longer periods of use before the battery needs to be charged.
Low speed, low power BLDC motors are used in
direct-drive turntableA direct-drive turntable is one of two main phonograph designs being manufactured today. The other style is the belt-drive turntable. Each name is based upon the type of drive motor used...
s for "analog" audio discs.
Transport
High power BLDC motors are found in
electric vehicleAn electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
s and hybrid vehicles. These motors are essentially AC synchronous motors with permanent magnet rotors.
The
SegwayThe Segway PT is a two-wheeled, self-balancing transportation machine invented by Dean Kamen. It is produced by Segway Inc. of New Hampshire, USA. The name "Segway" is a homophone of "segue" while "PT" denotes personal transporter....
Scooter and
VectrixVectrix is an electric vehicle company based in Middletown, Rhode Island, United States, with research and development facilities in New Bedford, Massachusetts...
Maxi-Scooter use BLDC technology.
A number of electric bicycles use BLDC motors that are sometimes built into the wheel hub itself, with the stator fixed solidly to the axle and the magnets attached to and rotating with the wheel. The bicycle wheel hub is the motor. This type of electric bicycle also has a standard bicycle transmission with pedals, sprockets, and chain that can be pedaled along with, or without, the use of the motor as need arises.
Heating and ventilation
There is a trend in the
HVACHVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
and
refrigerationRefrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
industries to use BLDC motors instead of various types of
AC motorAn AC motor is an electric motor driven by an alternating current.It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the...
s. The most significant reason to switch to a BLDC motor is the dramatic reduction in power required to operate them versus a typical AC motor.
[http://blog.uscooler.com/index.php/tag/ec-motor/] While shaded-pole and permanent split capacitor motors once dominated as the fan motor of choice, many fans are now run using a BLDC motor. Some fans use BLDC motors also in order to increase overall system efficiency.
[http://highperformancehvac.com/hvac-ecm-blower-motors-hvac.html]
In addition to the BLDC motor's higher efficiency, certain
HVACHVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
systems (especially those featuring variable-speed and/or load modulation) use BLDC motors because the built-in microprocessor allows for programmability, better control over airflow, and serial communication.
Industrial Engineering
Industrial engineeringIndustrial engineering is a branch of engineering dealing with the optimization of complex processes or systems. It is concerned with the development, improvement, implementation and evaluation of integrated systems of people, money, knowledge, information, equipment, energy, materials, analysis...
is a broad area of engineering that includes design, manufacturing, computer control, automation and human factors integration. The application of brushless DC (BLDC) motors within industrial engineering primarily focuses on
manufacturing engineeringManufacturing engineering is a field dealing with different manufacturing practices and the research and development of processes, machines and equipment.-Overview:...
or
industrial automationAutomation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization...
design. In manufacturing, BLDC motors are primarily used for
motion controlMotion control is a sub-field of automation, in which the position or velocity of machines are controlled using some type of device such as a hydraulic pump, linear actuator, or an electric motor, generally a servo...
,
positioningIn robotics, an end effector is the device at the end of a robotic arm, designed to interact with the environment. The exact nature of this device depends on the application of the robot....
or
actuationA linear actuator is an actuator that creates linear motion .Mechanical and hydraulic actuation are the most common methods of achieving the linear motion...
systems.
BLDC motors are ideally suited for manufacturing applications because of their high power density, good Speed-Torque characteristics, high efficiency and wide speed ranges. But their low maintenance is perhaps the greatest advantage in the manufacturing environment. Since BLDC motors due not have a
commutatorA commutator is a rotary electrical switch in certain types of electric motors or electrical generators that periodically reverses the current direction between the rotor and the external circuit. In a motor, it applies power to the best location on the rotor, and in a generator, picks off power...
or brushes, they last much longer and require much less maintenance than
brushed DC motorsA brushed DC motor is an internally commutated electric motor designed to be run from a direct current power source.-Simple two-pole DC motor:The following graphics illustrate a simple, two-pole, brushed, DC motor.DC Motor Rotation...
.
Motion Control Systems
BLDC motors are commonly used as pump, fan and spindle drives in adjustable or variable speed applications. They can develop 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 a variable speed response, BLDC motors operate in an electromechanical system that includes an electronic
motor controllerA motor controller is a device or group of devices that serves to govern in some predetermined manner the performance of an electric motor. A motor controller might include a manual or automatic means for starting and stopping the motor, selecting forward or reverse rotation, selecting and...
and a rotor position feedback sensor. The motor controller electronically commutates the motor by providing a
pulse width modulated (PWM)Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....
output that is based on the speed setpoint and the actual rotor position to ramp the motor's speed up or down as required by the load.
Positioning and Actuation Systems
BLDC motors are used in industrial positioning and actuation applications. For assembly robots,
brushless stepperA stepper motor is a brushless, electric motor that can divide a full rotation into a large number of steps. The motor's position can be controlled precisely without any feedback mechanism , as long as the motor is carefully sized to the application...
or
servothumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
motors are used to position a part for assembly or a tool for a manufacturing process, such as welding or painting. Rather than the rotary output of BLDC motors used in motion control applications, BLDC linear actuators drive a ball screw to obtain a linear output that closes a switch to enable a component in a manufacturing process. BLDC motors are commonly used as linear actuators for valve control.
Stepper motor
The stepper motor is often used in microprocessor and microcontroller-based and robotic equipment, as it provides cost-effective open-loop positional control.
Semiconductor producers include
Infineon TechnologiesInfineon Technologies AG is a German semiconductor manufacturer and was founded on April 1, 1999, when the semiconductor operations of the parent company Siemens AG were spun off to form a separate legal entity. , Infineon has 25,149 employees worldwide...
,
Texas InstrumentsTexas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
and
MicrochipMicrochip can also refer to:* Integrated circuit, a set of electronic components on a single unit.* Microchip Technology, a company that makes popular 8, 16 and 32-bit microcontroller lines.* Microchip implant , a microchip implanted into animals....
. Infineon offers so-called LIN stepper motors used in applications such as instrumentation and gauges, CNC machining, multi-axis positioning, printers and surveillance equipment.
Model engineering
BLDC motors are a popular motor choice for
model aircraftModel aircraft are flying or non-flying models of existing or imaginary aircraft using a variety of materials including plastic, diecast metal, polystyrene, balsa wood, foam and fibreglass...
including helicopters. Their favorable power-to-weight ratios and large range of available sizes, from under 5 gram to large motors rated at thousands of watts, have revolutionized the market for electric-powered model flight.
Their introduction has redefined performance in electric model aircraft and helicopters, displacing virtually all brushed electric motors. They have also encouraged a growth of simple, lightweight electric model aircraft, rather than the previous
internal combustion engineIn radio-controlled modeling, a model engine is an internal combustion engine used to power a radio-controlled aircraft, radio-controlled car, radio-controlled boat, free flight and control line aircraft, and tether car models also use these engines....
s powering larger and heavier models. The large 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 mess compared to small
glow fuelGlow fuel is a generic term used to describe a fuel source used in model engines -- generally the same or similar fuels can be used in model airplanes, helicopters, cars and boats. Glow fuel can be burned by very simple two stroke engines or by more complicated four stroke engines and these...
internal combustion engines that are used is another reason for their popularity.
Legal restrictions for the use of combustion engine driven model aircraft in some countries have also supported the shift to high-power electric systems.
Their popularity has also risen in the Radio Controlled Car, Buggy, and Truck scene, where sensor-type motors (with an extra six wires, connected to
Hall effectThe Hall effect is the production of a voltage difference across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current...
sensors) allow the position of the rotor magnet to be detected. Brushless motors have been legal in RC Car Racing in accordance to
ROARRemotely Operated Auto Racers , abbreviated as ROAR, is the sanctioning body of competitive radio-controlled car racing in the United States and Canada...
(the American governing body for RC Car Racing), since 2006. Several RC Car Brushless motors, feature replaceable and upgradeable parts, such as sintered neodymium-iron-boron (rare earth magnets), ceramic bearings, and replaceable motor timing assemblies. These motors as a result are quickly rising to be the preferred motor type for electric on and off-road RC racers and recreational drivers alike, for their low maintenance, high running reliability and power efficiency (most Sensored motors have an efficiency rating of 80% or greater).
See also
- SEER
Seer or Seers or SEER may refer to:Predicting the future* A clairvoyant, prophet, oracle, or diviner* The Seer , a fictional character on the television series Charmed...
- Coefficient of performance
- Inrunner
The term inrunner refers to a type of brushless motor used in radio controlled models, especially in reference to their use in aircraft to differentiate them from outrunners....
- Outrunner
The term outrunner refers to a type of brushless motor primarily used in electrically propelled, radio-controlled model aircraft.This type of motor spins its outer shell around its windings, much like motors found in ordinary CD-ROM computer drives. In fact, CD-ROM motors are frequently rewound...
- Brushless AC electric motor
A Brushless AC electric motor, also known as a permanent magnet synchronous motor , is similar to a brushless DC electric motor in that the magnetic field of the rotor is supplied by the permanent magnets rather than by electromagnets. However, the stator windings of a brushless AC motor are ,...
External links