Electronic speed control
Encyclopedia
An 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. ESCs are often used on electrically powered radio controlled models.
An ESC can be a stand-alone unit which plugs into the receiver's throttle control channel or incorporated into the receiver itself, as is the case in most toy-grade R/C vehicles. Some R/C manufacturers that install proprietary hobby-grade electronics in their entry-level vehicles, vessels or aircraft use onboard electronics that combine the two on a single circuit board.
, but rather in a way that varies the switching rate of a network of field effect transistors, or FETs. The rapid switching of the transistors is what causes the motor itself to emit its characteristic high-pitched whine, especially noticeable at lower speeds. It also allows much smoother and more precise variation of motor speed in a far more efficient manner than the mechanical type with a resistive coil and moving arm once in common use.
Most modern ESCs incorporate a battery eliminator circuit
(or BEC) to regulate voltage for the receiver
, removing the need for receiver batteries. BECs are usually either linear
or switched mode voltage regulators.
DC ESCs in the broader sense are PWM
controllers for electric motors. The ESC generally accepts a nominal 50 Hz PWM servo input signal whose pulse width varies from 1 ms to 2 ms. When supplied with a 1 ms width pulse at 50 Hz, the ESC responds by turning off the DC motor attached to its output. A 1.5 ms pulse-width input signal results in a 50% duty cycle output signal that drives the motor at approximately half-speed. When presented with 2.0 ms input signal, the motor runs at full speed due to the 100% duty cycle (on constantly) output.
s or inrunner
s have become very popular with radio controlled airplane hobbyists because of their efficiency, power, longevity and light weight in comparison to traditional brushed motors. However, brushless DC motor controllers are much more complicated than brushed motor controllers.
The correct phase varies with the motor rotation, which is to be taken into account by the ESC: Usually, back EMF from the motor is used to detect this rotation, but variations exist that use magnetic (Hall Effect
) or optical detectors. Computer-programmable speed controls generally have user-specified options which allows setting low voltage cut-off limits, timing, acceleration, braking and direction of rotation. Reversing the motor's direction may also be accomplished by switching any two of the three leads from the ESC to the motor.
, for example, 25 ampere
s or 25 A. Generally the higher the rating, the larger and heavier the ESC tends to be which is a factor when calculating mass and balance in airplanes. Many modern ESCs support nickel metal hydride and lithium ion polymer batteries with a range of input and cut-off voltages. The type of battery and number of cells connected is an important consideration when choosing a Battery eliminator circuit
(BEC), whether built into the controller or as a stand-alone unit. A higher number of cells connected will result in a reduced power rating and therefore a lower number of servos supported by an integrated BEC.
generally have reversing capability; newer sport controls can have the reversing ability overridden so that it can be used in a race. Controls designed specifically for racing and even some sport controls have the added advantage of dynamic braking capability. Simply put, the ESC forces the motor to act as a generator
by placing an electrical load across the armature. This in turn makes the armature
harder to turn, thus slowing or stopping the model. Some controllers add the benefit of regenerative braking.
but infrequent braking and the low mass of bicycles limits recovered energy. An implementation is described in an application note for a 200 W, 24 V Brushless DC (BLDC) motor.
mode" which fixes the motor RPM to a set speed, greatly aiding CCPM
-based flight.
and elevator
function. This allows the pilot
to retain control of the plane
to glide or fly on low power to safety.
Electronic circuit
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...
with the purpose to vary an electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
's speed, its direction and possibly also to act as a dynamic brake. ESCs are often used on electrically powered radio controlled models.
An ESC can be a stand-alone unit which plugs into the receiver's throttle control channel or incorporated into the receiver itself, as is the case in most toy-grade R/C vehicles. Some R/C manufacturers that install proprietary hobby-grade electronics in their entry-level vehicles, vessels or aircraft use onboard electronics that combine the two on a single circuit board.
Function
Regardless of the type used, an ESC interprets control information not as mechanical motion as would be the case of a servoServomechanism
thumb|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...
, but rather in a way that varies the switching rate of a network of field effect transistors, or FETs. The rapid switching of the transistors is what causes the motor itself to emit its characteristic high-pitched whine, especially noticeable at lower speeds. It also allows much smoother and more precise variation of motor speed in a far more efficient manner than the mechanical type with a resistive coil and moving arm once in common use.
Most modern ESCs incorporate a battery eliminator circuit
Battery eliminator circuit
A battery eliminator circuit is an electronic circuit designed to deliver electrical power to other circuitry without the need for a battery. Historically the expression was sometimes used to describe devices used to power battery-driven equipment from mains electricity...
(or BEC) to regulate voltage for the receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
, removing the need for receiver batteries. BECs are usually either linear
Linear regulator
In electronics, a linear regulator is a voltage regulator based on an active device operating in its "linear region" or passive devices like Zener diodes operated in their breakdown region...
or switched mode voltage regulators.
DC ESCs in the broader sense are PWM
Pulse-width modulation
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....
controllers for electric motors. The ESC generally accepts a nominal 50 Hz PWM servo input signal whose pulse width varies from 1 ms to 2 ms. When supplied with a 1 ms width pulse at 50 Hz, the ESC responds by turning off the DC motor attached to its output. A 1.5 ms pulse-width input signal results in a 50% duty cycle output signal that drives the motor at approximately half-speed. When presented with 2.0 ms input signal, the motor runs at full speed due to the 100% duty cycle (on constantly) output.
Brushless ESC
Brushless motors otherwise called outrunnerOutrunner
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...
s or inrunner
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....
s have become very popular with radio controlled airplane hobbyists because of their efficiency, power, longevity and light weight in comparison to traditional brushed motors. However, brushless DC motor controllers are much more complicated than brushed motor controllers.
The correct phase varies with the motor rotation, which is to be taken into account by the ESC: Usually, back EMF from the motor is used to detect this rotation, but variations exist that use magnetic (Hall Effect
Hall effect
The 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...
) or optical detectors. Computer-programmable speed controls generally have user-specified options which allows setting low voltage cut-off limits, timing, acceleration, braking and direction of rotation. Reversing the motor's direction may also be accomplished by switching any two of the three leads from the ESC to the motor.
Classification
ESCs are normally rated according to maximum currentElectric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
, for example, 25 ampere
Ampere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
s or 25 A. Generally the higher the rating, the larger and heavier the ESC tends to be which is a factor when calculating mass and balance in airplanes. Many modern ESCs support nickel metal hydride and lithium ion polymer batteries with a range of input and cut-off voltages. The type of battery and number of cells connected is an important consideration when choosing a Battery eliminator circuit
Battery eliminator circuit
A battery eliminator circuit is an electronic circuit designed to deliver electrical power to other circuitry without the need for a battery. Historically the expression was sometimes used to describe devices used to power battery-driven equipment from mains electricity...
(BEC), whether built into the controller or as a stand-alone unit. A higher number of cells connected will result in a reduced power rating and therefore a lower number of servos supported by an integrated BEC.
Cars
ESCs designed for sport use in carsRadio-controlled car
Radio-controlled cars are self-powered model cars or trucks that can be controlled from a distance using a specialized transmitter...
generally have reversing capability; newer sport controls can have the reversing ability overridden so that it can be used in a race. Controls designed specifically for racing and even some sport controls have the added advantage of dynamic braking capability. Simply put, the ESC forces the motor to act as a generator
Electrical generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...
by placing an electrical load across the armature. This in turn makes the armature
Armature (electrical engineering)
In 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....
harder to turn, thus slowing or stopping the model. Some controllers add the benefit of regenerative braking.
Electric Bicycles
A motor used in an electric bicycle application requires high initial torque and therefore uses Hall sensor commutation for speed measurement. Electric bicycle controllers generally use brake application sensors, pedal rotation sensors and provide potentiometer-adjustable motor speed, closed-loop speed control for precise speed regulation, protection logic for over-voltage, over-current and thermal protection. Sometimes pedal torque sensors are used to enable motor assist proportional to applied torque and sometimes support is provided for regenerative brakingRegenerative brake
A regenerative brake is an energy recovery mechanism which slows a vehicle or object down by converting its kinetic energy into another form, which can be either used immediately or stored until needed...
but infrequent braking and the low mass of bicycles limits recovered energy. An implementation is described in an application note for a 200 W, 24 V Brushless DC (BLDC) motor.
Helicopters
ESCs designed for radio-control helicopters do not require a braking feature (since the one way bearing would render it useless anyhow) nor do they require reverse direction (although it can be helpful since the motor wires can often be difficult to access and change once installed). Many high-end helicopter ESCs provide a "GovernorGovernor (device)
A governor, or speed limiter, is a device used to measure and regulate the speed of a machine, such as an engine. A classic example is the centrifugal governor, also known as the Watt or fly-ball governor, which uses a rotating assembly of weights mounted on arms to determine how fast the engine...
mode" which fixes the motor RPM to a set speed, greatly aiding CCPM
Cyclic/collective pitch mixing
Used in radio-controlled helicopters, Cyclic/collective pitch mixing reduces mechanical complexity and increases precision of control of the helicopter rotor's swashplate.- Conventional operation :...
-based flight.
Airplanes
ESCs designed for radio-control airplanes usually contain a few safety features. If the power coming from the battery is insufficient to continue running the electric motor the ESC will reduce or cut off power to the motor while allowing continued use of ailerons, rudderRudder
A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...
and elevator
Elevator (aircraft)
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's orientation by changing the pitch of the aircraft, and so also the angle of attack of the wing. In simplified terms, they make the aircraft nose-up or nose-down...
function. This allows the pilot
Aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...
to retain control of the plane
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
to glide or fly on low power to safety.