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What is an ESC and why does my RC car or truck need one? This article introduces the basics of the Electronic Speed Controller covering some of the common questions we get from customers. For the purposes of this article, we will be concentrating on electronic speed controllers in the context of RC cars, but some of the concepts also apply to drones.

What are they and what do they do?

The Electronic Speed Controller (ESC) can be thought of as brain of our vehicles, a complex processing unit that allows them to move at the pull of a trigger. Typically they control the speed and direction of the motor by constantly altering the power feed from the battery, in response to control signals taken from the receiver (that they also often power).

Think of them as a middleman. Having collected an instruction to accelerate from the wireless transmitter, the receiver will task the speed controller to accelerate the car with 80% power. The ESC will take power from the battery, adjust it to suit the instruction (polarity, ferocity etc) before passing it to the motor, which in turn spins to generate forward motion with the model. These instructions are updated multiple times a second, the ESC continuously modulating power to the motor as to the drivers requirements.

All shapes and sizes

Gone are the days of external BEC's and resistors hooked up to basic 3-speed mechanical (in this case rotating) speed-controllers actuated by servos like this:

Photo property of Metro Hobbies Australia


Electronic speed controllers now come in varying packages depending on what they are suitable for. They range from integrated all-in-one units such as FTX's 3-in-1 Receiver/ESC/Steering servo combo seen below:

FTX Colt RC remote control buggy review receiver esc

To more serious, standalone, compact, configurable units with large-gauge silicone wiring, cooling fans, anodised heat sinks, huge capacitors, jumper settings, sensor wires, data ports and powerful BEC's. You can find the ESC in your model by tracing the motor or battery wiring to it, see if you can identify the ESC's in the photos below.

Powering up

Speed controllers often feature the 'master power' button for the vehicle. This can be in the form of a single button (such as the EZ-set on the blue Traxxas ESC) or a small two-position switch on a fly-lead seen below.

Other units such as Axial's AE-5 are 'live' as soon as you plug the battery in.

ESC wiring plugs

Speed controllers are at the centre of the electronic system on an RC model. As such they have connections for the battery, motor, receiver and more. The battery connector you will be most familiar with, typically two thick silicone wires (often one red, one black) terminated with an XT60/EC3/Tamiya/Traxxas or deans/star connector.

electronic speed controller introduction primer

Brushed ESC's will typically have a pair of wires feeding to the motor (seen with bullet connectors on the red/black wires feeding the Maverick unit above) whilst brushless ESC's tend to have three or more wires such as blue/yellow/white marked cables on the Traxxas TRX unit below.

Traxxas XO-1 speed controller

There will also be a slim multi-wire cable with a 3-pin plastic connector on the end that plugs into the receiver unit.

Battery chemistry flexibility

A single type of battery connector can be used for multiple types of battery chemistry (NiMH, LiPo, Li-Ion etc) so if it is unable to auto detect type, it is important to manually set the ESC to it.

ESC's that require setting, typically feature a jumper that needs moving in accordance with the manual or an information sticker on the side as seen on the Axial and Kyosho models above.

Adjusting Settings : Programmable ESCs

Basic ESC have limited configuration, handled by a startup process or by a jumper setting. This is often limited to setting the end points and neutral position in conjunction with the transmitter, as seen in the instruction booklet below.

Traxxas TRX4 Brushless absima a10 manual

More expensive ESC's can be configured in greater detail just by a single 'set' button and feedback LED found on the unit or on a breakaway box alongside the power button. The manual included with the unit will provide instructions on how the set button and readout LED can be manipulated to customise the settings as seen in the table below.

More advanced ESC settings can be adjusted via a plug-in programming card, a special USB adaptor plugged into a computer, or more recently, a wireless dongle that connects to an app on your smartphone where settings can be altered.

Hobbywing's wifi express module provides a wifi link to their advanced ESC's

Settings that can be adjusted include LiPo cutoff voltage, running mode, reversing force, thermal cutoff temps, BEC voltage, drag brake function/ferocity, throttle curve and much, much more.

What is a BEC?

BEC stands for battery elimination circuit. Without going into too much detail, modern ESC's feature internal circuits that provide a regulated power supply, intended for running receivers and steering servos without needing to run extra cables from the battery to power these devices directly. They will prioritise this power supply to ensure you can retain control of the model during full power runs where the motor might demand all of the energy from the battery.

Traxxas TRX-4 Light kit installation lighting module standard esc

The Traxxas XL5-HV ESC shown above has battery eliminator circuitry powerful enough to run the receiver, steering servo, two extra micro-servos for the diff locks and an extensive LED lighting kit.

Where can i get a replacement?

Modern ESC's are impressively reliable but not always bulletproof. If yours has fried after an ill-advised trip through a puddle, all is not lost. We stock a selection of brushed and brushless ESC's compatible with a whole host of RC cars. Our staff can also advise on compatible alternative units or even upgrades!

RC Geeks : RC Nerds

This is part of a series of primer articles introducing RC terms. Interested in learning more? Read our introduction to transmitters, our battery introduction, a brief explanation of brushless RC cars, explanation on charging batteries alongside plenty of other tutorial articles. If you found this article helpful, or noticed any errors, please leave a comment below.

Written by

Tom Begley

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