disponible en franšais
I - Introduction
Use on RC planes from many years, brushless system appears recently on RC
cars. Particularly in racing, brushless systems are a new parameter and
some change in race's rules allowed racers to use them; as example, Jon
Orr won the ROAR Carpet Championship last march with a 1/12 pan car. So,
those systems are allowed in racing in some countries and will be allowed
in some others. The main criteria is the technology used to control the
motor, clearly speaking, it is about sensored and sensorless systems!
First, have a look to the brushed system and after that we will se deeply
inside the brushless world with sensored and sensorless systems
- Brushed System
Ok, first some recall on brushed ESC & motors, we've got below two -
on many more - high class ESC: three wires, one goes directly to the motor,
a second goes directly to the batteries and the last one links battery and
motor. For motor side, brushes and spring are located in the head. The
basic principle on brushed system is the following: the current comes from
the battery via the ESC and goes to the motor and specially the commutator
with the help of the brushes, brushes push on the commutator by springs.
Electric current creates after some magnetic field, counteract by the
magnet on the static part. That's it!
Here we are with brushed system, classical, working for ages with a lot of
success. It looks simple to tune - and it is! People get a lot of
experience with those system and particularly motor, motor which can be
tuned to obtain the maximum in performance. To have some increases in
performance, good brushes, spring and a correct head timing help a lot
with a well build and balanced motor, as others parameters. So, it works
fine like that. Nevertheless, there are some drawbacks. On the ESC side,
no thing special, the point is more on the motor side. As we see
previously, a brushed motor is equipped with ... brushed, obviously! Those
brushes pushed on the commutator by springs get weary after some runs.
Either the technology always push forward the limit, one day or another,
brushes need to be change and commutator need to be machine. Also, springs
can get lazy and have to be change as well.
III - Brushless System
1 - Background
Important: Brushless system
are not for beginners, experience in driving, chassis tuning, gearing and
batteries are highly needed due to performances offered by those
What is a brushless system? How is it looks like? What is it on? And many
Here are two brushless motor and ESC, which that make a brushless system.
Compared with the brushed system, the motor got no brushes - so is
denomination -, no spring and no commutator. For the ESC, five power wires
get out the electronics "box". As it can be seen on one ESC's
picture, two wires are dedicated to battery and three to motor.
But how it works? For ESC, current get in on one side, the battery wires
side and get out on the motor wires side. The main difference is on motor
design. As see, the brushed motor get a commutator, the brushless motor
not. The key point is the layout. On a brushed motors, magnets are on the
stator and the inductance on the rotor. The brushless motor layout is
reversed, magnets on the rotating part, inductance on the static part. The
positive point for brushless comparing with brushed motor is that there is
no brushes wear, no lazy springs. Due to the limited mechanical fiction, a
brushless motor run freely and so increase runtime. Also, rotating masses
are reduced and that gives another favorable point for brushless: higher
RPM. The reduced rotating masses get also less inertia and so greater
Here is about the general theory, now the practical cases. Brushless
system are devided in two classes, the sensored and the sensorless.
The sensored system use a ... sensor, for those who tend to be lost, and
sensorless not. The sensor is use to control/detect the rotor's position.
The sensorless doesn't use a sensor but the electronics part is slightly
complicated in term of control. We do not push forward here, electronics
matter can reveal some tricks only interesting for specialist.
Last point and not the least, some brushless ESC are compatible with
brushed motors. Some examples below show that fact.