Corally

Article disponible en français

        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


        II - 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 equipments

What is a brushless system? How is it looks like? What is it on? And many more questions.

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 acceleration.

Brushless Rotor

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.

	Brushless Setup	Brushed Setup