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An electronic speed control or ESC is a device mounted onboard an electrically powered radio control model in order to vary its drive motor's speed, its direction and even to act as a dynamic brake in certain controllers.

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 RC vehicles. Some RC 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.

Regardless of the type used, an ESC interprets control information not as mechanical motion as would be the case of a servo, but rather in a way that varies the switching rate of a network of field effect transistors, or "FET's." 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 extra batteries. ESCs are normally rated according to maximum current (amps) supported, for example, 25A. 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 voltages. The type of battery and number of cells connected is an important consideration for the BEC.

Novak GT7 electronic speed control and power capacitor for high-performance racing R/C cars and trucks

ESCs designed for sport use in cars 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. This puts the voltage being generated by the motor back to work recharging the vehicle's drive batteries. On full-sized vehicles, regenerative braking is used in electric and hybrid golf cars and hybrid automobiles while dynamic braking is used in diesel-electric locomotives to help slow trains on long downgrades.

Castle Creations Phoenix-25 brushless electronic speed control for R/C aircraft. Note the three motor leads exiting the unit to the right

ESCs for electric powered airplanes are very similar to those used in cars. However, features like reverse are not needed. Some units like the Castle Creations Phoenix-25 pictured at right may be programmed to spin the motor in either forward or reverse depending on the application. Dynamic brakes are used to stop a propeller from windmilling allowing folding props used on gliders to fold in, therefore reducing drag.

Brushless motors have recently become very popular in the radio controlled airplane scene. Brushless DC motor controllers are much more complicated than brushed motor controllers. They have to convert the DC from the battery into phased AC (usually three phase) that the brushless motor can use. The correct phase varies with the motor rotation, which is where the complication lies. Usually, back EMF from the motor is used to detect this rotation, but variations exist that use magnetic or optical detectors. Computer-programmable speed controls generally have user-specified options which allows setting low voltage cut-off limits, timing, and braking. Reversing the motor's rotational direction is achieve by switching any two of the three leads from the ESC to the motor, not by the ESC.

• Castle Creations
• Novak Electronics
• Radio controlled model