Brushless DC electric motor
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 a direct-drive design.
[5][7][6] It consists of a rotating cylinder or disc divided into multiple metal contact segments on the rotor.
In brushless DC motors, an electronic controller replaces the brush commutator contacts.
[5][7][6] 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.
Brushed DC motors develop a maximum torque when stationary, linearly decreasing as velocity increases.
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 the commutator, and an overall reduction of electromagnetic interference (EMI).
Controller software can be customized to the specific motor being used in the application, resulting in greater commutation efficiency.
Because the controller implements the traditional brushes' functionality, it needs to know the rotor's orientation 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.
Simple controllers employ comparators working from the orientation sensors to determine when the output phase should be advanced.
Outrunners typically have more poles, set up in triplets to maintain the three groups of windings, and have a higher torque at low RPMs.
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.
Brushless motors are found in many modern cordless tools, including some string trimmers, leaf blowers, saws (circular and reciprocating), and drills/drivers.
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.
[21] Brushless DC motors are widely used as servomotors for machine tool servo drives.
DC stepper motors can also be used as servomotors; however, since they are operated with open loop control, they typically exhibit torque pulsations.
Their favorable power-to-weight ratios and wide range of available sizes have revolutionized the market for electric-powered model flight, displacing virtually all brushed electric motors, except for low powered inexpensive often toy grade aircraft.
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 is another reason for their popularity.
Legal restrictions for the use of combustion engine driven model aircraft in some countries,[citation needed] 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.
These motors provide 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).
[26] Brushless motors are capable of producing more torque and have a faster peak rotational speed compared to nitro- or gasoline-powered engines.
Larger brushless RC motors can reach upwards of 10 kilowatts (13 hp) and 28,000 r/min to power one-fifth-scale models.
