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An electronic speed control (ESC) is an electronic circuit that controls and regulates the speed of an electric motor. It may also provide reversing of the motor and dynamic braking. Miniature electronic speed controls are used in electrically powered radio controlled models. Full-size electric vehicles also have systems to control the speed of their drive motors.
An electronic speed control follows a speed reference signal (derived from a throttle lever, joystick, or other manual input) and varies the switching rate of a network of field effect transistors (FETs). [1] By adjusting the duty cycle or switching frequency of the transistors, the speed of the motor is changed. The rapid switching of the current flowing through the motor is what causes the motor itself to emit its characteristic high-pitched whine, especially noticeable at lower speeds.
Different types of speed controls are required for brushed DC motors and brushless DC motors. A brushed motor can have its speed controlled by varying the voltage on its armature. (Industrially, motors with electromagnet field windings instead of permanent magnets can also have their speed controlled by adjusting the strength of the motor field current.) A brushless motor requires a different operating principle. The speed of the motor is varied by adjusting the timing of pulses of current delivered to the several windings of the motor.
Brushless ESC systems basically create three-phase AC power, like a variable frequency drive, to run brushless motors. Brushless motors are popular with radio controlled airplane hobbyists because of their efficiency, power, longevity and light weight in comparison to traditional brushed motors. Brushless DC motor controllers are much more complicated than brushed motor controllers. [2]
The correct phase of the current fed to the motor varies with the motor rotation, which is to be taken into account by the ESC: Usually, back EMF from the motor windings is used to detect this rotation, but variations exist that use separate magnetic (Hall effect) sensors or optical detectors. Computer-programmable speed controls generally have user-specified options which allow 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.
ESCs are normally rated according to maximum current, for example, 25 amperes (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, lithium ion polymer and lithium iron phosphate 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, if it uses a linear voltage regulator. A well designed BEC using a switching regulator should not have a similar limitation.
Most modern ESCs contain a microcontroller interpreting the input signal and appropriately controlling the motor using a built-in program, or firmware. In some cases it is possible to change the factory built-in firmware for an alternate, publicly available, open source firmware. This is done generally to adapt the ESC to a particular application. Some ESCs are factory built with the capability of user upgradable firmware. Others require soldering to connect a programmer. ESC are usually sold as black boxes with proprietary firmware. As of 2014, a Swedish engineer named Benjamin Vedder started an open source ESC project later called VESC. [3] The VESC project has since attracted attention for its advanced customization options and relatively reasonable build price compared to other high end ESCs. [4]
Large, high-current ESCs are used in electric cars, such as the Nissan Leaf, Tesla Roadster (2008), Model S, Model X, Model 3, and the Chevrolet Bolt. The energy draw is usually measured in kilowatts (the Nissan Leaf, for instance, uses a 160 kW motor that produces up to 340 Nm torque ). Most mass-produced electric cars feature ESCs that capture energy when the car coasts or brakes, using the motor as a generator and slowing the car down. The captured energy is used to charge the batteries and thus extend the driving range of the car (this is known as regenerative braking). In some vehicles, such as those produced by Tesla, this can be used to slow down so effectively that the car's conventional brakes are only needed at very low speeds (the motor braking effect diminishes as the speed is reduced). In others, such as the Nissan Leaf, there is only a slight "drag" effect when coasting, and the ESC modulates the energy capture in tandem with the conventional brakes to bring the car to a stop.
ESCs used in mass-produced electric cars usually have reversing capability, allowing the motor to run in both directions. The car may only have one gear ratio, and the motor simply runs in the opposite direction to make the car go in reverse. Some electric cars with DC motors also have this feature, using an electrical switch to reverse the direction of the motor, but others run the motor in the same direction all the time and use a traditional manual or automatic transmission to reverse direction (usually this is easier, since the vehicle used for the conversion already has the transmission, and the electric motor is simply installed in place of the original engine).
A motor used in an electric bicycle application requires high initial torque and therefore uses Hall effect sensors for speed measurement. Electric bicycle controllers generally use brake application sensors and 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 assistance proportional to applied torque and sometimes support is provided for regenerative braking; however, infrequent braking and the low mass of bicycles limit recovered energy. An implementation is described in a whitepaper by Zilog on an ebike hub motor controller [5] for a 200 W, 24 V brushless DC electric (BLDC) motor. [6]
P.A.S or PAS may appear within the list of components of electric conversion kits for bicycles, which implies Pedal Assistance Sensor or sometimes Pulse Pedal Assistance Sensor. Pulse usually relates to a magnet and sensor which measures the rotational velocity of the crank. Pedal pressure sensors under the feet are possible but not common. [7]
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.
Electronic speed controls for model RC vehicles may incorporate a battery eliminator circuit to regulate voltage for the receiver, removing the need for separate receiver batteries. The regulator may be linear or switched mode. ESCs, in a 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 motor attached to its output. A 1.5 ms pulse-width input signal drives the motor at approximately half-speed. When presented with 2.0 ms input signal, the motor runs at full speed.
ESCs designed for sport use in cars generally have reversing capability; newer sport controls can have the reversing ability overridden so that it can not be used in a race. Controls designed specifically for racing and even some sport controls have the added advantage of dynamic braking capability. 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.
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 "governor mode" which fixes the motor RPM to a set speed, greatly aiding CCPM-based flight. It is also used in quadcopters.
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, rudder and elevator function. This allows the pilot to retain control of the airplane to glide or fly on low power to safety.
ESCs designed for boats are by necessity waterproof. The watertight structure is significantly different from that of non-marine type ESCs, with a more packed air trapping enclosure. Thus arises the need to cool the motor and ESC effectively to prevent rapid failure. Most marine-grade ESCs are cooled by circulated water run by the motor, or negative propeller vacuum near the drive shaft output. Like car ESCs, boat ESCs have braking and reverse capability.
Electronic Speed Controllers (ESC) are an essential component of modern quadcopters (and all multirotors), offering high power, high frequency, high resolution 3-phase AC power to a motor in an extremely compact miniature package. These craft depend entirely on the variable speed of the motors driving the propellers. Fine speed control over a wide range in motor/prop speed gives all of the control necessary for a quadcopter (and all multirotors) to fly.
Quadcopter ESCs usually can use a faster update rate compared to the standard 50 Hz signal used in most other RC applications. A variety of ESC protocols beyond PWM are utilized for modern-day multirotors, including, Oneshot42, Oneshot125, Multishot, and DShot. DShot is a digital protocol that offers certain advantages over classical analog control, such as higher resolution, CRC checksums, and lack of oscillator drift (removing the need for calibration). Modern day ESC protocols can communicate at speeds of 37.5 kHz or greater, with a DSHOT2400 frame only taking 6.5 μs. [8] [9]
Most electric model trains are powered by electricity transported by the rails or by an overhead wire to the vehicle and so the electronic speed control does not have to be on board. This is however not the case for model trains with digital steering systems allowing multiple trains to run on the same track with different speed at the same time.
An anti-lock braking system (ABS) is a safety anti-skid braking system used on aircraft and on land vehicles, such as cars, motorcycles, trucks, and buses. ABS operates by preventing the wheels from locking up during braking, thereby maintaining tractive contact with the road surface and allowing the driver to maintain more control over the vehicle.
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate force in the form of torque applied on the motor's shaft. An electric generator is mechanically identical to an electric motor, but operates in reverse, converting mechanical energy into electrical energy.
Radio-controlled cars, or RC cars for short, are miniature model cars, vans, buses, trucks or buggies that can be controlled from a distance using a specialized transmitter or remote. The term "RC" has been used to mean both "remote controlled" and "radio controlled". "Remote controlled" includes vehicles that are controlled by radio waves, infrared waves or a physical wire connection. RC cars are powered by one of the three energy sources—electricity, nitro fuel or petrol. Electric RC models are powered by small but powerful electric motors and rechargeable nickel-cadmium (Ni-Cd), nickel metal hydride(NiMH), or lithium polymer (LiPo) cells with the former two being the most used. Both NiMH and LiPo have advantages and disadvantages in various RC applications where NiMH is mainly used for recreational and LiPo for more demanding purposes. There are also brushed or brushless electric motors—brushless motors are more powerful, long lasting and efficient, but also much more expensive than brushed motors.
A radio-controlled model is a model that is steerable with the use of radio control (RC). All types of model vehicles have had RC systems installed in them, including ground vehicles, boats, planes, helicopters and even submarines and scale railway locomotives.
A power inverter, inverter, or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of rectifiers which were originally large electromechanical devices converting AC to DC.
Electronic stability control (ESC), also referred to as electronic stability program (ESP) or dynamic stability control (DSC), is a computerized technology that improves a vehicle's stability by detecting and reducing loss of traction (skidding). When ESC detects loss of steering control, it automatically applies the brakes to help steer the vehicle where the driver intends to go. Braking is automatically applied to wheels individually, such as the outer front wheel to counter oversteer, or the inner rear wheel to counter understeer. Some ESC systems also reduce engine power until control is regained. ESC does not improve a vehicle's cornering performance; instead, it helps reduce the chance of the driver losing control of the vehicle.
A motor controller is a device or group of devices that can coordinate in a 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 regulating the speed, regulating or limiting the torque, and protecting against overloads and electrical faults. Motor controllers may use electromechanical switching, or may use power electronics devices to regulate the speed and direction of a motor.
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 the DC current pulses to control the speed and torque of the motor. This control system is an alternative to the mechanical commutator (brushes) used in many conventional electric motors.
A DC motor is an electrical motor that uses direct current (DC) to produce mechanical force. The most common types rely on magnetic forces produced by currents in the coils. Nearly all types of DC motors have some internal mechanism, either electromechanical or electronic, to periodically change the direction of current in part of the motor.
Drive by wire or DbW technology in the automotive industry is the use of electronic or electro-mechanical systems in place of mechanical linkages that control driving functions. The concept is similar to fly-by-wire in the aviation industry. Drive-by-wire may refer to just the propulsion of the vehicle through electronic throttle control, or it may refer to electronic control over propulsion as well as steering and braking, which separately are known as steer by wire and brake by wire, along with electronic control over other vehicle driving functions.
In electronics, a chopper circuit is any of numerous types of electronic switching devices and circuits used in power control and signal applications. A chopper is a device that converts fixed DC input to a variable DC output voltage directly. Essentially, a chopper is an electronic switch that is used to interrupt one signal under the control of another.
A variable-frequency drive is a type of AC motor drive that controls speed and torque by varying the frequency of the input electricity. Depending on its topology, it controls the associated voltage or current variation.
A servomotor is a rotary or linear actuator that allows for precise control of angular or linear position, velocity, and acceleration in a mechanical system. It constitutes part of a servomechanism, and consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.
A servo drive is an electronic amplifier used to power electric servomechanisms.
A transmission control unit (TCU), also known as a transmission control module (TCM), or a gearbox control unit (GCU), is a type of automotive ECU that is used to control electronic automatic transmissions. Similar systems are used in conjunction with various semi-automatic transmissions, purely for clutch automation and actuation. A TCU in a modern automatic transmission generally uses sensors from the vehicle, as well as data provided by the engine control unit (ECU), to calculate how and when to change gears in the vehicle for optimum performance, fuel economy and shift quality.
Brake-by-wire technology in the automotive industry is the ability to control brakes through electronic means, without a mechanical connection that transfers force to the physical braking system from a driver input apparatus such as a pedal or lever.
A Pedelec or EPAC, is a type of low-powered electric bicycle where the rider's pedalling is assisted by a small electric motor. However, unlike some other types of e-bikes, pedelecs are classified as conventional bicycles in many countries by road authorities rather than as a type of electric moped. Pedelecs have an electronic controller that cuts power to the motor when the rider is not pedalling or when a certain speed – usually 25 km/h (16 mph) or 32 km/h (20 mph) – is reached. Pedelecs are useful for people who ride in hilly areas or in strong headwinds. While a pedelec can be any type of bicycle, a pedelec city bike is very common. A conventional bicycle can be converted to a pedelec with the addition of the necessary parts, e.g., motor, battery, etc.
An outrunner is an electric motor having the rotor outside the stator, as though the motor were turned inside out. They are often used in radio-controlled model aircraft.
An electric skateboard is a personal transporter based on a skateboard. The speed is usually controlled by a wireless hand-held throttle remote, or rider body weight-shifting between front of the board for forward motion and rear for braking. As for the direction of travel to the right or left, it is adjusted by tilting the board to one side or the other. The classification of electric skateboards and legality of their use on roads or pavements varies between countries.
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