What Are RC ESCs — A Simple Guide

Joseph Flynt
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The world of radio controlled (RC) models is filled with jargon that can overwhelm newbies. Don’t worry—there’s less to grasp than first meets the eye. This guide looks at one of the common abbreviations—ESC. So, what are RC ESCs and why should you care? Well, ESC stands for Electronic Speed Controller. You’ll have a good understanding of ESC basics by the end of this page.

I also give the meanings of various other abbreviations throughout the piece. That makes this an all-in-one quick reference guide for RC terminology with the emphasis on ESCs.

Understanding the RC Communication Link

First, let’s look at where ESCs are in the RC communication link:

Operator (you) talks to the Transmitter (TX) -> TX talks to the receiver (RX) -> RX talks to Servos and Electronic Speed controllers (ESC) -> Servos move control surfaces -> ESC drives the motor. Control surfaces are the hinged movable parts of any RC model. They include things like the ailerons, rudder, and elevator on an aircraft. All this stuff happens behind the scenes, so why bother to learn more?

Some RC’ers like to understand how things work. Those who know how their RC vehicle functions become better operators. Some folks want to tinker and upgrade various parts of a model to enhance its performance. None of this is possible unless you know what to buy, how to install and/or configure it, and what the likely outcome is going to be.

Electronic Speed Control in Plain English

Here’s a simplistic breakdown of the vital role of an Electronic Speed Controller:

  • ESC is a circuit composed of tiny electronic components
  • ESCs can be built-in or standalone (removable) units
  • ESCs connect to an RC model’s electronic system
  • ESCs control an electric motor’s speed and thus the speed of an RC model
  • ESCs are the modern version of older, mechanical speed controllers
  • ESCs are more precise and efficient than the older systems above

ESCs Place in a Radio-Controlled Vehicle

Standalone ESCs are by far the favored option for RC enthusiasts. These tiny units fit straight into the throttle control channel of a receiver. So, all you do to upgrade or replace a faulty ESC is unplug the old and connect the new. That’s pretty much it. Installation is child’s play if you have the correct replacement part. Most cheap or toy-grade models have built-in ESCs, many of which are inseparable.

That’s why makers classify their models as either toy-grade or hobby-grade. It’s unlikely that anyone would want to swap the ESC or any other electronic part in a cheap toy. Some RC models sit between hobby and toy-grade quality and allow a little tinkering room for curious beginners.

Types of Electronic Speed Controllers

You now know what an ESC looks like and its job within a model. However, not all ESCs are equal.

  • ESCs are available in a vast variety of options
  • RC’ers choose ESC’s based on specific needs (see below)

ESCs differ in various ways. It’s the same with most electronic parts of a model. The ESC must fit and be compatible with whatever it is you’re upgrading. The primary considerations are types of motor, batteries, amperage, driving styles, and skill levels. Choosing the right ESC is not difficult if you know the workings of your model. The simplest ESC classifications are battery compatibility and motors.

How to Choose Your Next ESC

Buying the right ESC is not difficult when you know what to look for—specifically. That requires some cross-reference with other specs so that you can match the ESC with the model

Here’s a simple rundown of what to look for when choosing a new ESC:

  1. ESC has between 10–20% (no more) higher amp rating than the motor
  2. ESC can handle the same number of cells as the motor
  3. ESC has a built-in Battery Eliminator Circuit or BEC (see below)
  4. ESC must have a low cut off voltage, especially when running a LiPo

Let’s look at the four points above in more detail.

#1 Amp Rating

The maximum rating is expressed in amps like 25A, for example. That tells us what motor we can pair the ESC with. You can match the ESC amp rating with the motor’s max amperage draw. However, it’s better to use a higher amp rating, but not too high (see above). A 10–20% higher amp rating means the ESC runs quite cool and has some room to play with.

There are downsides if the ESC amp rating is either too low or too high:

  1. Too low: limits a motor’s power or risks overheating
  2. Too high: ESC becomes too big and heavy and thus hampers performance

#2 ESCs and Cells

Your new ESC must be able to handle the same number of cells that the motor can. You can find this easy on the specs of any engine and then match it with the ESC. What you’re doing here is looking for the max voltage that can go through the motor.

#3 ESCs and BECs

You need to know about something called a Battery Eliminator Circuit or BEC. A BEC delivers electrical power to your onboard radio system. It does away with the need for a separate battery to power 5V electronics. It’s better, therefore, to buy an ESC that has a built-in BEC (most of them do).

#4 Low Cutoff Voltage

Without a low cut-off voltage, the ESC will drain the Lipo until there’s nothing left. That mustn’t happen. LiPos should NOT be drained to less than 3 volts per cell. Consult the maker or ask in an RC community forum if you’re unsure about this or any of the other points above.

Advance ESC Specs

There are a few other things to consider when buying an ESC. I.ve touched on some of the significant ones below to give you a little insight. Which of these matter depend on the type of model.

  • ESC with reverse/dynamic braking
  • ESC with different modes
  • ESC with cooling systems
  • ESC with computer programming

Reverse/braking is vital for those that use such functions. Boats and land vehicles need them for maneuvering. But reverse/braking has no use for model planes and helicopters. Different products can benefit from particular modes like race, governor, and sports. And the programmable ESCs are for more advanced users.

Those who can program an ESC get to personalize or fine-tune how it works. Some examples are:

  • Battery type
  • Motor type, i.e. brushed, brushless
  • Control the low voltage cutoff point
  • Power curve
  • Acceleration
  • Reverse lockout
  • Current limiter
  • Braking patterns
  • Others

The programmable list can go on depending on the ESC, but you can see the potential.

Summing Up

That’s the ABCs of Electronic Motor Controllers. You should now know what they are, how they work, and what to look for. ESC mismatching is a common newbie blunder, but it doesn’t have to be. Make sure you refer to this guide when you’re ready to upgrade or replace an ESC in your RC models. You may want to print this page out and put a highlight through the parts that matter to you.