electronic speed control

 What is the Electronic Speed Controller (ESC)? it's a great component to correctly control the acceleration of any electric motor, and to avoid some damage. This great component is able to control the capacity of an electric motor. So the electronic speed controller has a very important function for any drone.


1. What does an electronic speed controller do?   

An Electronic Speed Controller (ESC for short) is an electronic circuit that does a basic yet essential job: running a motor. More specifically, ESCs control and regulate the speed of brushless motors. On top of that, there are also cases in which ESCs are used to supply the +5 volts that the flight controller’s servos and other electronics in the craft need to operate in.

To actually grasp in detail what it is that an ESC does, one has got to understand the many parameters that its settings can control. Traditionally, users are more interested in - or familiar with - the following functions and settings:

  • ● Brake

    When ESCs were originally brought to market, multi-rotors were still just a twinkle in the inventor’s eyes. So most pilots used them on helicopters, planes, and even gliders. Some models of this last type of aircraft sometimes had their propellers fold in flat against the body to improve aerodynamics and enter the gliding stage of the flight. So, when a pilot interrupts the throttle, what he/she wants is the motor/propeller on the glider to stop rotating as quickly as possible to allow the folding of the propellers. For purposes such as this, a brake function is quite useful.

  • ● Soft Start

    Soft Start is a setting that, when enables the ability to spin up the motor slowly and gradually so that, if the pilot was a little bit aggressive on the throttle, the ESC would slowly spin up the motor and, once it was up to speed, a much faster throttle response. This function is used mainly to avoid the speed controller just piling all the energy into the motor and stripping the cogs and gears in the model. To put it simply, it is like the opposite of the brake function but for the start and not the cut. Soft Start is to this day very useful to remote-control helicopters since it allows the pilot to simply take the throttle to the level where the aircraft is about to take off and let the ESC do the rest.

  • ● Motor Direction

    Users can define the direction of their motor (reverse or forward/default) by configuring this setting in the ESC. Another option is simply swapping any two of the three wires that are connected to the motor.

  • ● Low Voltage

    If the read voltage begins to drop below a certain level, this function of the ESC makes it reduce the power to the motor. This comes in handy for planes and gliders, but not so useful for helicopters, and, at last, something pilots should absolutely not enabled for multi-rotors.

  • ● Response Time

    This function regulates how quickly the ESC changes the motor speed after the command given by the pilot on the throttle. When setting this parameter, one should keep in mind that accelerating a motor, as well as the attached propeller, involves many physical limitations so do use this with moderation and conscience.

There are many other functions besides the ones that were just explained but these are probably enough to illustrate what traditional ESCs can do.



To understand how an Electronic Speed Control (ESC) works, one has to first know what it is that such device controls and how it basically works. Brushless Motors, which are ideal for drones, as well as for other types of RC aircraft, are built in such a way that they need to be controlled by ESCs.

A Brushless (BLDC) Motor is in its essence made out of two main parts: a stator and a rotor. Contrary to what is found in a Brushed Motor, Brushless Motor’s coils are not located on the rotor, and instead, are fixed on the stator and the rotor is a permanent magnet.

When current runs through a coil, it will create a magnetic field. So, if the appropriate current is applied, the coil will generate a magnetic field that will attract the rotor’s permanent magnet. Furthermore, if each coil is activated one after another, this magnet will keep on rotating as illustrated in the animation below.

The rotor’s magnet, which can have one or more pairs of poles, moves by accompanying the change in the direction of the magnetic fields generated in the stationary coils. Thus, to control the rotation, all the ESC needs to be able to do is properly adjust the direction and the magnitude of the current running in these coils.

Every Electronic Speed Controller receives a speed reference signal, given by the transmitter, corresponding to how high or low the pilot takes the throttle lever (or any other manual input device like a joystick). Then, in response to this signal, the ESC switches the rate of a network of field-effect transistors (FETs) on the stator.

By activating the appropriate FETs at the right time and sequence, a rotating magnetic field through the stator is created, and currents in the coils are generated. Subsequently, the speed of the rotor changes as it tries to keep up with the change in the switching frequency of said transistors. The rapid switching of the transistors is what causes the motor itself to emit its characteristic high-pitched whine, especially noticeable at lower speeds.



Every model of Electronic Speed Controller will have basically 3 different groups of wires, no matter what type of motor the user intends to connect it to. These groups can be distinguished as follows:

  • ●First off, there is a pair of black and red wires with a female connector at the end of each of them. These two wires - marked in red on the image below - are to be plugged into the battery.
  • ●Then, there is a group of wires that should be connected to the motor. By standard, each of these wires has a male connector at their end. This group might have 2 or 3 wires depending on the type of Motor (and ESC) used - if the motor is a Brushless type, then the ESC shall have 3 wires to connect to it, and if it is Brushed, it will have only 2 wires (a pair of black and red). On the image below, which shows an ESC from FrSky’s Neuron series, these 3 wires are marked in yellow.
  • ●And, finally, there is the group that is to be plugged into the receiver. As you can see on the image below, there are 5 pins marked in blue: two are for GND, one for the power source (BEC), one for the signal (PWM), and the last one for the Smart Port telemetry (we will go into this later).
    Traditionally, all the user has to do is connect the GND-BEC-PWM pins and the pins of a channel in the receiver to both communicate and power it.
    However, in case the receiver gets power from another source, then there is no need to activate the BEC function - actually, the user should not activate it at all in this specific case.

    FrSky ESC Neuron 40/60/80
  • Do notice that, on ESCs from the latest lines by FrSky, there is a pin labeled “S. Port”. By connecting this one to the pin under the same name on the receiver, the user will be able to get telemetry data from both the ESC and the RX using the Smart Port Communication Protocol.





Electronic Speed Controllers can vary a lot from model to model, and so does the way every pilot puts them to use. Thus, in this short tutorial, you will learn how to get going with your ESC, and the main discussion will be centered on how to calibrate it.

Do note that the instructions are focused on Brushless type ESCs since the majority of modern RC models, which are our primary focus here, fly with Brushless motors.

For starters, it’s important to have some knowledge on (brushless) ESCs, such as what they are supposed to do - as well as their most useful functions -, their basic working mechanism, and how to correctly wire them to the motor, receiver, and battery. On the Q&A section from Horus, there are some explanations on all of these topics so be sure to check them out if needed.

Once you have all the components ready, assuming that they can work perfectly fine (no product defect) and that the ESC was properly chosen considering the current rating, it is time to move on to the calibration. Follow the steps below for a manual ESC-by-ESC calibration:

  1. 1.Security Check! Before calibrating an ESC, you should ensure that your motor has no props on it and that the LiPo battery is disconnected (or any other kind of battery used);
  2. 2.Connect your ESC to the throttle channel of the receiver (usually the 3rd channel);
  3. 3.Turn on the transmitter and take the throttle stick to the maximum level (full up);
  4. 4.Plug the battery into the ESC. After doing so, you will probably hear a musical tone followed by two short beeps;
  5. 5.Once you hear the two beeps, lower the throttle stick to the minimum level (full down);
  6. 6.Then, the ESC will emit a sequence of short beeps (one for each cell in the battery being used) and at last a single long beep. This indicates the endpoints (corresponding to max and min throttle) have been set and the ESC is calibrated;
  7. 7.Disconnect the battery.

If it seems that the ESC’s was not successfully calibrated, then you might need to reverse the throttle channel on the transmitter. Another solution might be lowering your throttle trim on the transmitter to 50%.

As was said before, the ESC calibration process can vary based on what brand of ESC is being used. Thus, it is recommended to always refer to the manual that comes with your model for more detailed information (such as what each tone means as feedback ) or in case the instructions presented here do not work for your ESC.



If you have ever tried to run a Brushless motor with an Electronic Speed Controller, you probably got confused at some point because things were just not right. Then, you might have started wondering if your ESC was really working or if the problem was actually with the motor. The difficulty lies in the number of variables involved.

Be that as it may, it is recommended to first narrow down the focus of problem investigation to only one component (either the motor or the ESC) and then work on troubleshooting from there. To do this, there is a simple solution that should be followed with great care and caution: mix and match.

Mix and Match

If you have a motor and an ESC to spare that are both proven to be perfectly functional, you could try running the known-to-be-good motor with the suspect-for-defect ESC. Be careful! You should do this for only one click or two and then turn everything off quickly!

If this match (good motor + suspicious ESC) does not work properly too, then the problem might really be in the ESC. But, before jumping so fast into conclusions, you should repeat the test but the other way round - take the known-to-be-good ESC and try running the questionable motor with it.

You should be careful when running both of these two combinations - especially the second one - since a bad ESC is not likely to hurt a motor but a bad motor can kill an ESC. Furthermore, be warned that If you persist on testing for longer periods of time and higher throttle settings, other components involved will also be put at higher risk of damage.

Other basic tests

Besides the mix and match test, a voltage test with any cheap multimeter is also a good place to start: if there is no 5V on the wire that connects the BEC and the throttle channel, then the conclusion is that the receiver is not getting any power. If the ESC does not detect the presence of a receiver, it will not arm itself in most cases.

Another point worth mentioning is that If there is no motor present or if a malfunctioning motor is indeed present, most ESCs will also not arm.



When choosing an Electronic Speed Controller for your RC model, it is essential to take some points into consideration, such as the size of the motor, the choice of propeller, as well as the number of cells in the battery.

A racing drone’s robust brushless motor, equipped with an aggressive high-pitched propeller, for example, can pull more than 40 amperes of current. Therefore, selecting the right ESC is crucial so that the FETS on it will not be damaged by the high current and fail mid-flight.

As you can see, the ESC choice will be mostly defined by the amount of amperage it needs to be able to handle, and that depends on your choice of motor and propeller. However, do bear in mind that ESCs are also distinct in their rate of the number of battery cells, in other words, according to the voltage range that they were made to work with. To put it simply, taking the voltage into account when choosing an ESC is fairly simple and much more straightforward since voltage depends solely on the number of battery cells and battery type.

Considering the great variety of batteries available in the market nowadays (with different options of composition/chemistry and number of cells), the rule/restriction to follow when choosing an ESC ends up relying majorly on the amperage demand of your motor: what we want is to have the ESC be able to handle more power than the motor will draw.

So, choose the motor first. From that, get an ESC that meets the motor’s needs, and, finally, get a battery that fits the ESC’s restrictions and can supply a little more than the amp demand.

If the "draw current" of your motor is already known, then that is practically all you need to know to choose your Electronic Speed Controller - the ESC amp rating should be at least that much and preferably a bit higher (for safety reasons).

If you do not know the exact draw current, but only an estimated or rough value, then you might want to get a bigger ESC (one that will for sure be able to handle all the power and have room for much more). Of course, a bigger ESC will occupy a larger place in the model as well as weight a little more, but if these two disadvantages are of no big concern to you, then this will be a good solution.



All Electronic Speed Controllers come with two different specifications about the current/amperage they can endure: one is the continuous current and the other, the burst (or peak) current.

The continuous current is the maximum current you can safely draw for a long period of time (or continuously, as the name suggests) without compromising the ESC or other components in your system, such as the receiver connected to it.

The burst or peak current is the maximum current the ESC can handle for short periods of time, but with the cost of a cooldown period. The amount of time is usually specified by the ESC’s manufacturer, and it could vary between 5 seconds up to 25 seconds. If you can’t find the burst current time, the rule of thumb is to assume the lowest value of 5 seconds. As one would already expect, the value of the burst current is higher than that of the continuous current.

Pushing the ESC above its burst current can cause de-syncing or even damage it permanently, and worse-case-scenario, if it happens during your flight, it will probably also make your aircraft fall. So you need to keep in mind how much current your system will draw from the battery through your ESC into the motor and other components. That current depends on the number of cells of your battery (as well as its type), the size of the motor, as well as the chosen propeller.

You should not expect your ESC to work on its burst current, so when choosing one, it's best to use the continuous current specification, and give a little spare current, just to be safe. If you define your ESC based on its peak current (even if you mean to only use the burst for a short amount of time during the flight), you can risk it going into cooldown mid-flight and losing your RC model.

The common recommendation is to choose an ESC with 20% more continuous current rating than the propulsion system can draw. That way, in case you want to change propellers and motors, that extra current should allow a little flexibility.



As you might already know, a standard ESC has three sets of wires: the 1st set plugs into the model's main battery; the 2nd one has a standard servo wire that plugs into the throttle channel of the receiver; and, last but not least, the 3rd set of wires plugs into the motor and powers it. What you probably do not know is that you can choose to power the receiver either through the ESC (using that 2nd set of wires) or with an additional, smaller battery. (with lower tension).

In a time when the majority of RC models - mainly airplanes - still used combustion engines, the receiver and servos had to be powered by an additional battery dedicated specifically to them. Traditionally, this battery was a NiCd or NiMH type and offered 4.8V to 6V of tension. This is why all the servos and receivers from that time (and even nowadays) were made to work within this voltage range.

So, in the early stages of electric RC technology development as we know it today, when electric motors were just introduced as an option for RC models, it wasn't uncommon to use two batteries at the same time (one for the motor and another one just for the receiver), since the motor demanded a tension from the battery (7.4V to 44.4V) that was higher than the maximum voltage the receiver could handle. Some pilots chose to maintain this configuration until today for safety reasons and, in this particular case, the ESC does not power the receiver.

However, other pilots chose the modern alternative: a Battery Eliminator Circuit (or BEC for short) instead of an additional battery just for the receiver. This device steps the tension from the motor’s battery down to a lower voltage of 5V to 6V, allowing the receiver to also be powered by the same battery. It also eliminates the expense and added weight of a dedicated receiver battery.

Engineers also noticed that, for currents of small amperage (lower than approximately 50A), it is possible to join a BEC and an ESC under a single case/package and thus created an ESC that is also able to power the receiver with its internal BEC.

If you try to use the motor’s battery to power your receiver and servos through an ESC without a BEC, they just won’t turn on, unless you provide an additional battery.


Customer Reviews

Perfect solution for narrow fuselages! Review by Wilhelm
I use this small „FrSky 2.4GHz ACCESS ARCHER R6 RECEIVER“ in my 7 channel F5J gliders in conjunction with the FrSky Neuron 40S ESC or Neuron 60S ESC. I program the NEURON ESC‘s with the newest BL HELI SUITE 32 software on S-BUS output. Ailerons, flaps, elevator and rudder are connected directly to the receiver via the 6 PWM channel outputs and the NEURON ESC via S-BUS.
Perfect solution for narrow fuselages! - Great value and function!
(Posted on 10/1/2021)

Perfect solution for narrow fuselages! Review by Wilhelm
I use this small „FrSky ARCHER SR6“ receiver in my 7 channel F5J gliders in conjunction with the FrSky Neuron 40S ESC or Neuron 60S ESC. I program the NEURON ESC‘s with the newest BL HELI SUITE 32 software on S-BUS output. Ailerons, flaps, elevator and rudder are connected directly to the receiver via the 6 PWM channel outputs and the NEURON ESC via S-BUS.
Perfect solution for narrow fuselages!
(Posted on 10/1/2021)

FrSky Neuron 60S ESC with diminished size and optional BEC function
Perfect solution for narrow fuselages Review by Wilhelm
I flashed this NEURON 60S ESC with the newest BL HELI SUITE 32 software. So I can programmed the ESC to S-BUS output. Now I can also use the small ARCHER GR6 or ARCHER SR6 receivers in my 7 channel F5J gliders. Ailerons, flaps, elevator and rudder are connected via the 6 PWM channels and the controller via S-BUS.
Perfect solution for narrow fuselages!
(Posted on 9/29/2021)

FrSky Neuron 40S ESC with diminished size and optional BEC function
Perfect solution Review by Wilhelm
With the latest BL HELI SUITE 32 software, this NEURON 40S controller can be programmed to S-BUS output. Now I can also use the small ARCHER GR6 or ARCHER SR6 receivers in my 7 channel F5J gliders. Ailerons, flaps, elevator and rudder are connected via the 6 PWM channels and the controller via S-BUS.
Perfect solution for narrow fuselages! (Posted on 9/18/2021)

Works perfectly with Horus X10 on a EDF plane Review by Emilio
Setup is fairly simple and instructions are clear, the stablization works great currently only using normal mode but the plane tracks perfectly and wind does nothing to my plane, definetly buying another one, makes landings seem so easy as you only need to manage the plane speed and direction the stabilizer takes care of negating wind and making aproach really easy (Posted on 8/19/2021)

Good little receiver Review by Jan
If you do not need the telemetry for "normal" airplanes, you can use this cheap receiver!
Quality is very good for this price and it has full range!
Very light and small receiver, very impressed! (Posted on 7/19/2021)

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