Electronic speed controller
An Electronic Speed Controller (ESC) is an electronic device that is connected to a servo channel on the receiver and, rather than controlling the position of a servo, allows the signal from the receiver to control the speed and torque of the connected electric motor.
There are two types of electronic speed controller for the two different types of motor in common use:
- With a brushed motor, the speed is controlled simply by restricting the amount of power delivered to the motor. The easiest way for the speed controller to do this is to supply the power is short pulses, many times a second. The longer the pulses, the more power, and the faster the motor turns. Brushed motors connect to the speed controller via two wires; to reverse the direction of the motor, the wires are swapped.
- With a brushless motor, power is controlled in the same way, but the speed controller must electronically select between the multiple sets of windings in the motor to make it turn. Most modern brushless speed controllers are known as sensorless controllers and make use of the voltage generated (Back EMF) in the momentarily unpowered windings to determine the position of the motor. Virtually all brushless motors and controllers used in model helicopters have three wires; to reverse the direction of the motor, swap the connections of any two wires.
The ESC must be rated high enough to handle the maximum amount of current expected to be drawn by the motor at any given time.
Many ESCs for smaller (450 sized and below) helicopters include a battery eliminator circuit, allowing the 'high voltage' battery powering the main motor (via the ESC) also to power the flight electronics, which typically require a much lower voltage.
Most ESCs have a hot start prevention function, which prevents the ESC initializing until it sees a "low throttle" signal from the receiver. You may have to move your throttle trim towards the bottom to achieve this.
Most brushless ESCs use the motor as a speaker, and can make a range of tones to indicate the ESC's state, such as "armed" or "in programming mode".
Most ESCs are programmable to some degree. The programming mode is often accessed by powering up the ESC at full throttle; alternatively a programming card can be bought to configure the ESC more easily. Typical configurable settings include:
- Battery cutoff voltage, to prevent overdischarging lipo batteries.
- Soft start to prolong the life of components.
- Governor mode.
- Commutation timing adjustment.
- High and low throttle positions.
- Electronic speed control on Wikipedia.
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