Electronic Speed Controllers (ESCs)
An Electronic Speed Controller or ESC is an electronic circuit designed to vary an electric motor’s speed, its direction and possibly also to act as a dynamic brake. The types most often used for brushless motors essentially provide an electronically-generated three phase, low voltage, source of energy for the motor. Our ESC is a stand-alone unit which goes between the voltage source (Lipo) and the motor and has a separate control lead that plugs into the receiver’s throttle control channel.
Brushless ESC systems basically drive three-phase brushless motors by sending a sequence of signals to cause rotation of the magnetic field wich causes the motor’s moving part to rotate in sympathy. The correct phase sequence varies with the direction of motor rotation, which is to be taken into account by the ESC.
ESCs are normally rated according to maximum current, for example, 25 amperes ( 25A). Generally the higher the rating, the larger and heavier the ESC tends to be. This is a factor that must be taken into account when calculating mass and balance of your model. Most modern ESCs support Nickel Metal Hydride (NiMH) or Lithium Ion Polymer (Lipo) batteries and are programmed to detect the appropriate input and cut-off voltages. The type of battery and number of cells connected is an important consideration when choosing an ESC with a Battery Eliminator Circuit (BEC), whether built into the controller or as a stand-alone unit, to supply voltage to the receiver.
A Battery Eliminator Circuit (BEC) provides an appropriate voltage supply for the Receiver and Servos hence eliminating the need to carry a separate receiver battery. ESCs having a built in BEC circuit employ one of two methods:
a) Linear voltage regulator
b) Switching voltage regulator.
You don’t need to understand the technology of these options. Type a) BEC circuits suffer from falling power rating the more Lipo battery cells connected. This means that a lower number of servos can be supported by an integrated BEC, if it uses a linear voltage regulator.
A well designed BEC using a type b) switching regulator should not have a similar limitation.
ESCs using b) type regulators are generally more expensive than the more basic a) types. Having said this, for our purpose, an ESC with a linear regulator is more than capable of handling the three or four servos you will be using in your trainer from a three or four cell Lipo.
If you decide to purchase an ESC without a built in BEC circuit, you have the choice of using a “stand alone” BEC also known as a UBEC or a conventional receiver NiMH battery. Most “stand alone” BECs are of the switching variety so this problem should not arise. There is also an advantage to using a stand alone” BEC as heat build up within the ESC does not affect its performance. Under extreem circumstances, this can be the case with ESC/BEC combined circuits.