Controlling a radio-controlled (RC) model car is a skill. The ‘driver’ needs good control of the speed of the vehicle and the power being applied to the driven wheels.
Your Transmitter has either a trigger or stick to operate the ‘throttle’. The ESC (Electronic Speed Control) translates this movement by the driver into a signal that increases or decreases the power produced by the motor.
The signal from your transmitter is picked up by the Receiver in the model and, once decoded, is sent to the ESC. The ESC then converts this very small signal into much larger signals that are sent to the motor to turn the wheels of the model.
If you bought your RC car complete, the ESC that is fitted (which may be part of the receiver) will be carefully matched to the motor and battery supplied with the model.
If you build your own car from a kit you can choose from a wide variety of ESC’s at price points from under £50 to over £200. What you choose will depend on the type of motor you are using and the type of racing you are doing.
How does an ESC work?
The simplest form of speed control would be a switch you can turn on to make the motor run and then turn off to stop it. This is clearly not going make the model very controllable but that is where the hobby started.
Since Radio Controls systems became ‘proportional’ the control of the model’s speed has become much more sophisticated.
Motor speed controls send pulses of power from the battery to the motor. These pulses can be very narrow with a long gap between them, which will cause the motor to run slow, or very wide with almost no gaps, so the motor will run at full speed. An infinite variation is possible depending on how far you pull or push the transmitter control.
The speed control has electronic switches inside (FET’s, or Field Effect Transistors) that are turned on by the Control’s circuits to send a pulse of power to the motor, then switched off to stop the power. The frequency of these pulses can be from a few hundred per second to many thousands depending on the design and complexity of the ESC.
Types of ESC.
There are two types of Electric Motor that are used to power RC Cars and Trucks, Brushed and Brushless. Almost all ESC’s are designed to work with only one type of motor, either Brushed or Brushless.
A Brushed motor may look like these:
The first thing to notice is that it has two connections. The black motor above has access to the brushes for maintenance, the others are known as ‘closed end-bell’.
A Brushless motor may look like these:
Each of these Brushless motors has three connections to the coils. On the first one you can see a connector on the back cover, just below the letter ‘B’. This is called the sensor port. The Purple motor on the right does not have this port as it is a ‘sensor-less’ motor. Almost all Brushless motors used in Model Car Racing classes are fitted with sensors.
This is a typical modern ESC for Brushed Motors. You will see it has 4 thick wires, the Red and Black are the power connectors to the battery and the Blue and Yellow wires connect to the motor.
There is also a thin three wire cable that connects to your Receiver and another wire to the on off switch.
ESC’s such as this are simple to connect and easy to install.
This is a typical brushless ESC; you will see the same thick Red and Black wires that connect to the battery and the three-wire cable that connects to the Receiver (small blue plug) and the wires to the switch.
In addition, we now have three thick wires that connect to the Motor (Blue, Yellow and Orange) and an extra device attached to two thin red and black wires. The extra device is a Capacitor. It connects across the battery connections and its purpose is to filter out high frequency noise to protect your ESC.
Hidden from view is the sensor port that also connects to the motor using a sensor cable which usually comes with the motor.
So clearly this is a lot more complex and harder to install in our vehicle.
Is it worth the effort? Well in short, yes. In the first instance most Racing Classes now use Brushless motors and you have to use the correct motor for the class you want to race in. Secondly Brushless motors require very little maintenance and have a very long life.
A brushless ESC is more complex than a brushed ESC, so the two types of motor are not normally usable on the same ESC. There is always a but though. The largest maker of RC cars is Tamiya and they supply an ESC with some of their kits that can be used with both types of motor, but it is very much the exception.
A Brushless motor has three coils wound around the inside of the case with a magnetic rotor which spins in the centre. The ESC has to send power to the three coils at the right time to attract the magnetic rotor and make it spin in the correct direction. This means the ESC needs to know where the magnet in the rotor is. That is the job of sensors inside the end of the motor which connect to the ESC via the sensor lead.
But didn’t you mention sensor-less motors? These use a different design of ESC that senses the rotors position using the motors own coils. As the magnet sits under a coil it changes the characteristic of the coil, so the ESC can work out which way to send the signals to make the motor move. Early versions of this had issues with ‘stuttering’ at the start as the motor could be sent the wrong way and then quickly corrected, this is why racing classes all adopted the sensor design.
Getting it stopped……
As well as controlling the power going to the motor, the ESC can also apply the brakes. When the motor is spinning, whatever type of motor is in use, the spinning magnet causes the coils to work like a generator to produce electricity.
If no power is being applied to the motor and we place an electrical load across the motor leads, that load will slow the rotation of the motor, so slowing the model.
The ESC switches the load across the motor as you move the throttle trigger or stick away from neutral in the reverse of the throttle direction.
Most Brushless ESCs use even more complex braking techniques to send pulses to the coils to ‘repel’ the magnet as it approaches a coil (remember the sensor lead tells the ESC where the magnet is) and so slow the rotation of the motor. None of these techniques work when the model is stopped, so they cannot work when it is parked on a slope for instance, but normally produce enough braking to judge your entry to a corner.
Getting it backwards….
Back when we all used Brushed motors, there were two types of ESC’s, serious racing ESC’s which were forwards only, and Reversing ESC’s which were not for real racers were they?
Now that we all use Brushless Motors, all the ESC’s can produce reverse, but the transmitter trigger or stick only has two directions of travel. If Reverse is enabled on the ESC normally the first movement of the stick or trigger to the reverse will put the brakes on, and the second movement will give reverse. You may find this helpful while you are learning, but you get better control over the brakes if the ESC is set to ‘Forwards Only”.
Adjusting the ESC.
A brushed Esc may have some controls to set the Operating mode (FWD/Brake, FWD/Reverse etc), the type of battery in use (LiPo or NiMh) and maybe the neutral position from the Transmitter.
Brushless Speed Controls have many more adjustments but hardly any controls. Usually there will be a ‘set-up’ button that you use to program the ESC to match your transmitter, so Neutral is Neutral, FWD is FWD and full FWD is max power.
For the other more detailed parameters you normally need an external programming box.
This will allow you to access a large number of parameters which affect the way your ESC and motor behaves. Different manufacturers use different interfaces, so one box will not work with every ESC out there unfortunately.
The Program Box will also allow you to connect your ESC to a Laptop or other computer so you can update the program in the ESC and adjust m any more parameters.
Some Manufacturers have systems that allow you to connect to the ESC via wi-fi or Bluetooth so you can adjust the ESC from a mobile phone, which can be very useful trackside.
This is certainly an advanced area of the topic and your Retailer or fellow club racers should be able to help you through the maze. You will find a wealth of information on Manufacturer web sites, YouTube and the internet in general.
It’s all about the timing…and what is Blinky about?
All Electric Motors can be ‘tuned’ to spin faster if you change the time when the current switches through the coils.
On Brushed Motors this was done by rotating the end bell with the brushes. This moved the point at which current was switched by the commutator relative to the magnets in the motor.
Brushless motors can be adjusted the same way, most now have adjustable end-bells so the sensors can be moved in relation to the coils. You can just make out a scale on this enlarged view of a motor shown earlier:
But the complex electronics in a Brushless ESC also allows you to vary the timing electronically in real time as the motor is driving the model, this is known as ‘Turbo advance’ as it can give a surge in power when it ‘cuts in’ not unlike a turbo on a full size car. This is commonly used in ‘Modified’ or ‘Open’ Class racing.
Many ESC’s have a special mode when these advanced tuning modes are inaccessible. This is called a ‘Zero Timing’ mode.
When the ESC is in this mode the status LED on the ESC is made to flash (or blink) if the transmitter is at neutral. That is why this mode was called ‘Blinky’, initially in the US, and then in the RC racing world in general. This is often a feature of ‘Spec’ or ‘Stock’ class Racing. The Blinking LED is used by Scrutineers to check that the ESC’s are legal for this class of racing.
Selecting your ESC
If you have joined a Club and have an idea what you want to race, ask around at the Club and most Racers will be only too happy to help. If you buy a model that is popular at your local club, there will always be someone there who can help you set it up.
Your first choice will depend on the type pf motor, Brushed or Brushless.
If you will be running a Brushless motor are you entering a class that runs a ‘Blinky’ set-up? If so, make sure you select an ESC that offers a “Blinky” or Zero Timing option. Most do but do check carefully. Most Hobby Shops or On-Line stores will have several ranges to choose from, almost all are made in the Far East, but some have UK importers, and this will help if you have problems.
You do not need to buy the most expensive model for your first ESC, look out for the lower priced models or maybe even Second Hand. You can upgrade to the higher priced options when your skill level and pocket allows. Save your money for Race Fees, Practise makes perfect!