Electronic Speed Controller

Which ESC is right for you?

What is an Electronic Speed Controller?

An electronic speed controller (ESC) is what controls how fast the motors turns. The ESC plugs into the throttle channel of the receiver.

The factors that determine what ESC to use include the type of motor you have, the size of the motor, and the type of batteries.

Brushless or Canned Motor?

ESC's designed specifically for brushed motors will only work with brushed motors. Likewise, electronic speed controllers designed specifically for brushless motors will only work for brushless motors. There are a few ESC's that are designed to work with both.

In layman's terms, a brushed ESC simply turns the voltage on and off very rapidly(several times a second). To increase the speed, the ESC increases the amount of time that the voltage is on while decreasing the amount of time that the voltage is off. This is called "chopping" the voltage. To slow the motor down, this process is reversed.

The brushes on a brushed motor determine how the electromagnets are energized to keep the motor spinning. For a more in depth explanation of how brushless RC motors work click here. A brushless ESC has the added task of determining how each pole needs to be energized at any given time to keep the motor spinning. The brushless ESC needs to have feed back from the motor in order to perform this task.

Why? The brushes on a brushed motor are in a fixed position relative to the permanent magnets. When the armature rotates, the brushes contact the plates of the commutator at the perfect spot each revolution to keep the motor turning. Without feedback, the ESC on a brushless motor has no idea where the permanent magnets are in relation to the electromagnets(poles).

All brushless motors and brushless ESC's have three wires. Only two of the three wires are energized by the ESC at any given time. The pole that is not energized (coasting) will actually generate a small amount of voltage that is proportional to how fast the motor is turning. This small voltage is used by the ESC to determine how fast and in what direction the motor is turning at any given time. With this information, the ESC knows how to charge the electromagnets to keep the motor turning.

How big is your motor?

Electronic speed controllers are rated for a maximum current. The more current an ESC is rated for, the more expensive and heavier it will be. Choose an electronic speed controller that is rated for slightly more than what your motor will pull at full throttle. Too much current will damaged an electronic speed controller very quickly!

What type of battery?

LiPo batteries will be permanently damaged if the voltage of any cell drops below 3.0 volts. For this reason, LiPo batteries require an electronic speed controller with a low voltage cutoff (LVC). The LVC will cut the power to the motor when the voltage reached 3.2V, or whatever you set the LVC to be.

You will want to choose an ESC that can handle the voltage of the battery pack you plan to use. The voltage rating for each ESC is clearly stated in the specifications.

Battery Eliminator Circuit (BEC)

The motor requires much more power than the receiver and speed controller. A battery eliminator circuit(BEC) converts the voltage from the motor battery to a lower voltage for the receiver and ESC. This eliminates the need for a separate low voltage battery for the receiver and ESC.

The BEC also senses when the battery is getting low and cuts power to the motor while allowing the servos to function for a safe landing.

The BEC is usually incorporated circuit board of the ESC for small to medium size electric airplanes. Large RC airplanes that require larger voltages to power the motor will require a stand-alone BEC, which is called a voltage regulator.