Brushless Electronic Speed Controllers.
When looking at a brushed motor, it is easy to see how they are controlled quite simply by limiting the amount of voltage available to the motor.
This could be done with a simple mechanical switch, a slightly more elaborate but still mechanical sliding potentiometer,
or ultimately, with a relatively sophisticated, but still simple, electronic box to vary the voltage.
The electronic box is called an Electronic Speed Controler, or ESC. (Mechanical speed controllers can be known as MSCs).
Generation 1 - A new dawn.
Brushless motors are a little more sophisticated, in that each of the coils needs to be powered in sequence, and kept in synch with the
motor speed as it varies from 0 rpm up to speeds in excess of 50,000 rpm, as well as varying the voltage required to energise each coil.
Modern brushless ESCs are sophisticated pieces of electronics with appreciable amounts of computing power.
This first generation of ESCs had to do all that the previous brushed ESCs were capable of, setting punch control to ramp the voltage in,
altering the braking forces, and setting safety cut-outs for when the voltage dropped too low, being just a few.
They also compute where the rotor has moved to, and so when to apply power to the next coil.
They do this in two ways, sensored or unsensored.
The Sensored ESCs and motors are linked together with a lead of small wires which relay information between the motor and the ESC.
This way, the ESC knows, exactly where the rotor is in the motor, because the sensor has relayed that data down the lead.
The ESC then times the pulse of energy to the next coil so that the rotor is given the required push or pull at exactly the right time to either accelerate or slow it.
Unsensored motors and ESC are not connected by sensor wires. Unsensored motors, dont have any sensors in them, reducing costs.
Sensored motors can be used without the sensor lead, but many are not as efficient to run this way, as a motor designed to be unsensored.
Without the feedback from the motor, the ESC effectively has to guess what the motor is doing. It applies pulses to the coils in the motor in such a way
that the motor will respond to the inputs whatever it was doing before. This is far less precise, and to an extent. less efficient than having
a sensored setup, so the sensorless concept has more or less fallen by the wayside as far as onroad racing is concerned.
Generation 2 - Do more.
After Brushless motors had been around for a while, the manufactureres started to ask what else could be done with the onboard processing power,
to differentiate themselves from what other manufacturers were offering.
Generation 2 BL-ESCs were able to set throttle profiles, brake profiles, current limits, the same as Gen 1 ESCs.
But crucially, it was realised that motor timing could be controlled by the ESC rather than mechanically altering the relationship between the coils
and sensors on the motor.
Up to now, if you wanted to alter the timing of a motor, you had to physically move the endbell of the motor.
(Anticlockwise to advance the timing, and clockwise to retard the timing).
On a 540 size motor diameter, 1mm of movement on the endbell is approx. 3 degrees of timing.
On a brushed motor you are moving the brushes relative to the coils, on a brushless motor, you move the sensors relative to the coils.
The effect, (of advancing the timing), is to swap revs and power for efficiency, and current draw. You also swap revs for torque.
All this means that if you advance the timing too far, (to get the revs and the power you crave), you reduce the torque to the extent that
the motor cannot pull properly out of the corners, and in extreme cases, cannot pull away from a standing start.
The first Generation 2 speedos allowed you to set brushless timing in software, on the ESC, without moving the endbell on the motor.
Clearly this can only work where the sensors are operative, and relaying information back to the computer chip on the ESC.
Therefore, all ESCs which can alter motor timing, are sensored by definition.
It was then a short step to alter the timing, while the motor was running, so that you had torque to pull away,
but then over a certain number of revs, advance the timing some more to increase the power.
The first Gen 2 ESCs which did this were relatively crude, and had only a limited number of set profiles to chose from, which perfromed this "trick".
But they were very effective. Suddely, everone needed to upgrade their ESC, and the old Gen1, and early Gen2 (sometimes known as Gen1.5) ESCs
were effectively obsolete.
Generation 3 - Turbo.
The so called third generation of ESCs, took this concept further, and provided a number of profiles, which set and varied the timing advance
according to a number of different conditions.
The best of the new crop of ESCs, provided a computer interface to allow you to program your own profile of dynamic timing into the ESC,
where you could set the rpm when timing started to be added, when it should stop, and how fast to add the timing.
This capability started to become known as Boost, or in some cases Turbo.
Some manufacturers also allowed software updates, which meant that you didn't need to buy a new ESC every time new ideas surfaced.
In 2009, another new innovation. As well as dynamically advancing the timing with the rev profile, the ability to add in a flood of timing when
the throttle had been fully open (Wide Open Throttle), for a set period. The manufacturer who helped to pioneer these innovations, Tekin, called
this capability TURBO, and therefore called the existing capability, (to ramp in timing according to revs), BOOST.
Back to the Future?
By this time, to get the best from your ESC meant you had to have a computer, and you needed to be able to think about what the motor was
theoretically doing on each corner of the circuit you were driving.
Some drivers think it has all gone a bit far, and are promoting a new class of zero timed ESCs.
Either where the ESC doesn't have the capability to dynamically advance the timing (Gen1), or can be configured to blink a light to show that it
currently isn't doing so.
At Adur, we call this class, "Sportsman Stock", and limit the motor type to 17.5 Brushless. This class is surprisingly close in performance to
the "old" Stock 27 turn brushed class, which everyone used to start with a few years back.
You'll hear people talking about Gen1, Gen2 and Gen3 ESCs a lot, but when challenged to place a specific definition it's hard. In truth, there is a
lot of overlap between the generations, and so there is no definitive time when Gen1 became Gen2, or even a guide to say that ESC 'X' belongs to a
Some people will just divide into Gen1 (not able to set dynamic timing), and Gen2 (able to set boost and turbo timing dynamically).
Broadly speaking though
- Cannot alter the motor timing at all.
- Can alter the default timing of the motor. The same as twisting the endbell on the motor. (STATIC TIMING)
- Can alter motor timing on the fly depending on motor RPM. (BOOST)
- Can add in timing depending on detection of Wide Open Throttle. (TURBO)
How to set up a Gen 3 ESC.
With all of these different parameters, it can be easy to lose sight of the basics, and get lost in the available options.
The first thing you should set up is the gearing you are going to run on the car.
Most manufacturers say, or have said, that you should "gear to temperature".
What does that mean exactly?
In the Generation 1 days, where the maximum revs of the motor was pretty much set by the available voltage in the battery, the only way to
get the car to go faster, was to alter the gearing. As Brushless motors do not have the friction of the brushes limiting revs and efficiency.
You can continue to raise the gearing in pursuit of speed until the motor gets hot enough to melt solder, heat fracture metal components and burn out coils.
Therefore each motor manufacturer has a guideline temperature which should not be exceeded at the end of the 5 minute race.
Temperature is measured with a heat gun type of thermometer at the endbell of the motor as soon as the race is over. The internal temperature can be much higher of course.
With gen 3 ESCs the situation can be more complex, so we don't gear to temperature any more, but we should still aim not to exceed the manufacturers limit at the end of 5 minutes.
1) Set gearing.
To set the gearing of the car, take all of the timing, boost and turbo out of the ESC.
Drive the track paying particular attention to the punch out of the infield corners. don't worry at all about how fast the car is along the straights.
Alter the gearing up or down until your progress through the twisty parts of the track is optimised. i.e., you are driving fast through the infield and getting out of the corners as quickly as your car setup will allow.
2) Add static timing.
Either on the endbell of the motor, or on the ESC, add timing to the motor as long as it doesnt slow your corner exit speeds, and impact you times through the infield.
3) Add boost timing.
For boost, you need to think about...
Again, don't worry about top speed down the straight. Turbo can fill this gap.
- At what number of rpm you want to start adding extra timing
- How much extra timing you can add
- At what rpm you can should the timing feeding in, (which gives you the overall "ramp")
Boost impacts acceleration between corners. If you start feeding it in too early, the motor will not have enough torque to punch out of the corner.
Too late, and you wont get the benefit of the extra timing, and other cars will out accelerate you between corners.
The trick is to find the best start and stop parameters, and amount of timing to go fastest through the infield on a given track.
Adding too much timing to the boost, or ramping it too quickly just adds heat to the motor as you are feeding in energy which the motor cant use.
Boost will raise your speeds down long straights, but it's primary mission is to get you from corner to corner quicker.
4) Add Turbo.
You have 3 parameters to play with here. The amount of extra timing to feed in, how quickly it ramps in, and how long after WOT is detected before it starts.
How much timing to add is tricky. Again, you don't want to add so much that the motor can use it, and gets hot instead.
This then is a function of what speed you are doing on entry to the main straight, when you hit full throttle, and also of how much timing you have already got for static and boost.
I normally start with a further 10 degrees on top of that already specified, and then add a couple of degrees at a time until the car goes no faster at the end of the straight.
The ramp can be used to fine tune how quickly the car accelerates onto turbo, and can be useful to calm the back end of the car if you are accelerating into the corner onto the straight.
How long after WOT before the turbo comes in, is dependant on your driving style, but can be used to avoid the turbo cutting in, if you use full throttle on other parts of the track, where it is not needed, or wanted.
There are of course, many opinions on how to set up these generation 3 ESCs, some prefer to avoid the issue altogether and buy an ESC such as the LRP or Nosram range, which don't require a PC to set it up, and you can simply select from the Pre-defined profiles.
Some people will disagree with what I have written above, or think it's too much trouble, life is too short, and "please give me some settings to start with".
However, more than ever, the ESC settings are personalised to your driving style, as well as the motor characteristics and the track layout.
Paying attention to how the car is working, and altering the ESC settings to suit you, will pay dividends in the long run.
This technique works for me, and if nothing else, I'm sure it will start a debate.