Brushless DC electric motor (BLDC motors, BL motors) also known as electronically commutated motors (ECMs, EC motors) aresynchronous motors that are powered by a DC electric source via an integrated inverter/switching power supply, which produces an AC electric signal to drive the motor. In this context, AC, alternating current, does not imply a sinusoidal waveform, but rather a bi-directional current with no restriction on waveform. Additional sensors and electronics control the inverter output amplitude and waveform (and therefore percent of DC bus usage/efficiency) and frequency (i.e. rotor speed).
The rotor part of a brushless motor is often a permanent magnet synchronous motor, but can also be a switched reluctance motor, orinduction motor.
Brushless motors may be described as stepper motors; 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 brushless motor principles, though there is overlap.
Two key performance parameters of brushless DC motors are the motor constants Kv and Km.
Brushless vs. brushed motors
Brushed DC motors have been in commercial use since 1886. Brushless motors, on the other hand, did not become commercially viable until 1962.
Brushed DC motors develop a maximum
torque when stationary, linearly decreasing as velocity increases.
[5] Some limitations of brushed motors can be overcome by brushless motors; they include higher efficiency and a 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 which rotate around a fixed
armature, eliminating problems associated with 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.
Brushless motors offer several advantages over brushed DC motors, including more torque per weight, more torque per
watt (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 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 a
microcontroller or
microprocessor computer, or may alternatively be implemented in analogue hardware, or in digital firmware using an
FPGA. Commutation with electronics instead of brushes allows for greater flexibility and capabilities not available with brushed DC motors, including speed limiting, "micro stepped" operation for slow and/or fine motion control, and a holding torque when stationary.
The maximum power that can be applied to a brushless motor is limited almost exclusively by heat;
[citation needed] too much heat weakens the magnets
[6] and may damage the winding's insulation.
When converting electricity into mechanical power, brushless motors are more efficient than brushed motors. This improvement is largely due to the brushless motor's velocity being determined by the frequency at which the electricity is switched, not the voltage. Additional gains are due to the absence of brushes, which reduces mechanical energy loss due to friction. The enhanced efficiency is greatest in the no-load and low-load region of the motor's performance curve.
[citation needed] Under high mechanical loads, brushless motors and high-quality brushed motors are comparable in efficiency.
[citation needed][disputed – discuss]
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.
Controller implementations[edit]
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 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 the need for separate Hall effect sensors, and therefore are often called
sensorless controllers.
A typical controller contains 3 bi-directional outputs (i.e. frequency controlled three phase output), 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
microcontroller 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-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 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.
Variations in construction[edit]
Schematic for delta and wye winding styles. (This image does not illustrate the motor's inductive and generator-like properties)
Brushless motors can be constructed in several different physical configurations: In the 'conventional' (also known as
inrunner) configuration, the permanent magnets are part of the rotor. Three stator windings surround the rotor. In the
outrunner (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 or axial flux 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 brushless motors, the coils are stationary.
There are two common electrical winding configurations; the delta configuration connects 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 speed, but can give higher top speed. Wye configuration gives high torque at low speed, but not as high top speed.
[7]
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 driven 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.
Applications[edit]
The four poles on the stator of a two-phase brushless motor. This is part of a computer cooling
fan; the rotor has been removed.
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 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 turntablesfor
gramophone records.
Transport[edit]
High power brushless motors are found in
electric vehicles and
hybrid vehicles. These motors are essentially AC synchronous motors with permanent magnet rotors.
The
Segway Scooter and
Vectrix Maxi-Scooter use brushless motors.
A number of
electric bicycles use brushless 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.
[8]
Heating and ventilations[edit]
There is a trend in the
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 the dramatic reduction in power required to operate them versus a typical AC motor.
[9] While
shaded-pole and
permanent split capacitor motors once dominated as the fan motor of choice, many fans are now run using a brushless motor.
[when?] Some fans use brushless motors also in order to increase overall system efficiency.
[10]
In addition to the brushless motor's higher efficiency, certain
HVAC systems (especially those featuring variable-speed and/or load modulation) use brushless motors because the built-in microprocessor allows for programmability, better control over airflow, and serial communication.
Industrial engineering[edit]
Brushless motors are ideally suited for manufacturing applications because of their high power density, good speed-torque characteristics, high efficiency and wide speed ranges and low maintenance. The most common uses of brushless DC motors in industrial engineering are linear motors. servomotors, actuators for industrial robots, extruder drive motors and feed drives for CNC machine tools.
[11]
Motion control systems[edit]
Brushless 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.
[12] To obtain a variable speed response, brushless motors operate in an electromechanical system that includes an electronic
motor controller and a rotor position feedback sensor.
[13]
Brushless dc motors are widely used as
servomotors for machine tool servo drives. Servomotors are used for mechanical displacement, positioning or precision motion control. In the past DC
stepper motors were used as servomotors; however, since they are operated with
open loop control, they typically exhibit torque pulsations.
[14] Brushless dc motors are more suitable as servomotors since their precise motion is based upon a closed
loop control system that provides tightly controlled and stable operation.
Positioning and actuation systems[edit]
Brushless motors are used in industrial positioning and actuation applications.
[15] For assembly robots,
[16] brushless stepper or
servo motors are used to position a part for assembly or a tool for a manufacturing process, such as welding or painting. Brushless motors can also be used to drive linear actuators
[17]
Motors that directly produce linear motion are called
linear motors. The advantage of linear motors is that they can produce linear motion without the need of a
transmissionsystem, such as a ball-and-lead screw, 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, a motor controller excites the coil windings in the actuator causing an interaction of the magnetic fields resulting in linear motion.
[18] Tubular linear motors are another form of linear motor design operated in a similar way.
Model engineering[edit]
Legal restrictions for the use of combustion engine driven model aircraft in some countries[clarification needed] have also supported the shift to high-power electric systems.Brushless motors are a popular motor choice for
model aircraft including
helicopters. Their favorable power-to-weight ratios and large range of available sizes, from under 5 gram to large motors rated at well into the
kilowatt output range, have revolutionized the market for electric-powered model flight, displacing virtually all brushed electric motors. They have also encouraged a growth of simple, lightweight electric model aircraft, rather than the previous
internal combustion engines 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 fuel internal combustion engines is another reason for their popularity.
Radio controlled cars[edit]
Their popularity has also risen in the
radio controlled car area. Brushless motors have been legal in North American RC car racing in accordance to
ROAR since 2006. These motors provide a great amount of power to RC racers and, if paired with appropriate gearing and high-discharge
Li-Po (lithium polymer) or considerably safer
LiFePO4 batteries, these cars can achieve speeds over 100 miles per hour (160 km/h).
[citation needed]
Brushless motors are capable of producing more torque and have a larger peak RPM compared to nitro or gasoline powered engines.
Nitro engines climax to peak at around 46,800 RPM and 2.95HP, while a smaller brushless motor generally maximum torque start then tapering off can reach 50,000 RPM and 5HP.
We grabbed our usual assortment of tools to make the board. Our fine tip 15 watt soldering iron, a set of "helping hands," a tube of solder some pliers and pair of diagonal or flat cutters. Of course, we always keep a multi-meter handy.
Take a few 
The real star is this little guy. It's a MP3 / WAV decoder and headphone amp all in one. Soldering this chip to the board is the single most difficult, but important part of the build.
To mount the SMD chip, we tinned the solder pads with some solder. If you've got some liquid flux, your life will be easier later on. If you don't, just don't cook the solder too much as you tin the pads. Be sparing, it doesn't take much.
Yeah, yeah, we know this looks ugly, but we prettied it up later. Place the chip on the pads and heat each pin to melt the solder onto it. While the rest of the board is clear, make sure you've got a solid connection at each pin. You can 
There are two crystals in the kit. The marked crystal is 24.576Mhz, while the unmarked is 10Mhz. They're not polarized, so they can be mounted in either direction, just be sure to put them in the right locations.
After each component is soldered on, we trim each lead. We've found that flat cutter like these leave duller edges and help reduce flying bits.
If you haven't worked with resistor networks before, you'll be missing a vital bit of information. The dot on the end indicates the common lead. This corresponds with the bar on the resistor nets in the instruction diagram.
With long components, we usually solder one lead, and position the part while it's still hot. After that, finishing the job is easy. (To ensure good connections, make sure you heat the lead, then melt the solder on the hot tip/part lead.)
The headphone jack has fairly large leads. Since it's another surface mount component, we tinned the pads before mounting it. You can get away without doing it -- in fact, we didn't bother when we installed the SD card jack.
Make note of the position of the notch on the DIP jack for the PIC controller. It won't effect operation, but the notch indicates the pin numbering. It's good to be in the habit of following the standard.
The symbol for a diode looks like a triangle with a bar across one corner. The bar indicates the cathode of the diode -- the line on the end of the diode also indicates the cathode. Make sure you orient these in the proper direction before soldering them down.
The shape of the leads on the .01uf capacitors is by far the most annoying part of the build. They are too wide for all of the mounting holes.
The fix is simple enough. Grab a pair of pliers and carefully straighten the leads. Just don't torque on the lead near the body of the capacitor! 
Once that's done, the biggest pain in the neck is placing all the caps in the various board locations. We noted a botched stencil mask job here - the labels for c11 and c12 overlap with the solder pads for the decoder chip. Ah well, we got the idea.
Mounting the voltage regulator is easy, just spread the leads a bit and insert it. The flat face corresponds with the stencil on the board.
This 10uf capacitor requires a bit of a bending job. Make sure to orient the leads correctly before you bend them.
The cap doesn't quite fit between the resistor net and the chip socket. We bent the network over a bit and made sure it didn't interfere with chip insertion.
The biggest flaw in the instructions has to do with the LEDs. LEDs are polarized - The instruction sheet only notes the flat side of the LED to indicate polarity -- but the small LEDs that come with the kit lack a flat side. The short lead on the LED also indicates the cathode. So insert the LEDs with the short lead at the flat notation of the LED on the board. Careful now!
When you try to install the PIC controller chip, you'll find that the leads are a bit wider than the socket. This is always the case with DIP hardware. To fix it, place the edge on a flat surface and push down gently. The idea is to bend all the pins uniformly.
We powered our Daisy up with 5v from our bench top PSU. (Modified PC power supply) We noted some noise from the PSU in the sound output - battery power prevents this.
The most interesting feature of this mp3 player is the flexibility of the configuration. Thanks to all the inputs and jumper configurations, the player can be customized to perform in most ways you can think of. We wish it included a USB port to allow the memory card to be easily accessed. For now you'll need something else to load your songs with. The various d-pins are temporarily grounded to tell the player what to do: track, volume, pause, etc.
