The simplest place to start with a discussion on brushless motors is the fact that they have no brushes (hence the term brushless!). This is significant in two ways. The first is that it removes a large amount of friction from the motor operation. The second is that it means there is no direct conduction through the motor that would allow it to turn with a connection of power to the motor, hence the need for a brushless motor controller in order to obtain rotary motion from a brushless DC motor.
Whereas a traditional DC motor had brushes which conducted power from the stator to the rotor and back out again, therefore driving the turning force, a brushless motor relies on motor phases being turned on and off in sequence in order to drive the motor round.
A brushless motor has the electromagnets on the stator and the permanent magnet on the rotor.
Depending on the type of brushless motor being used it can have a range of different specifications including a different number of poles however the key switching implications the different electromagnets mounted on the stator on and off in order to move the permanent magnet Rotor around.
If one imagines the process with a very simple setup with 2 sets of poles (arranged in pairs) then it is easy to see how this works with the central magnet being in 90 degree movements across the two pole pairs.
1. Coil 1 Positive-
2. Coil 2 Positive-
3. Coil 1 Negative
4. Coil 2 Negatives
As the electromagnets are switched on and off in this sequence they would therefore move the permanent magnet rotor around.
Based on the sequence above would seem logical that the motors performance would be rather jumpy, in the same way a stepper motor can often be seen to be taking fixed steps.
The reason this can be avoided is largely down to the type of motor controller which is used and how it is set up.
In order to get the principle of the brushless motor across we have used a very simplified example but it is important to remember that the coils would not simply be switched on and off (as in full power on/full power off) but rather can be gradually powered off and on in order to smooth out the motor turning.
At low speeds with a low number of poles in the motor it is still quite possible that a of jumpiness might be observed (this is why many lower speed use use stepper motors rather than brushless) but at higher speeds and with the right type of controller in use this will be smoothed out by a combination of the mass on the shaft (operating in the same way as a flywheel operates), the controller and the speed. For more information and guidance on motor ‘cogging’ or jumpiness and how to remove it then please click here.
The permanent magnet is on the rotor and the electromagnets are on the stator.
By powering the electromagnets in sequence it is possible to move the permanent magnet around and therefore turn the motor.
Different motors have different numbers of poles and the more poles there are the smoother the motor typically be.
Now that we understand the basic principles of brushless motor performance and how they work, it is worth considering why we might choose to use brushless motors over brushed DC motors.
The removal of the brushes has several major advantages:
1. Brushes wear out over time due to friction. The typical lifespan for brushed motors is around 2000 hours whereas a brushless motor typically will last 10000 hours (please note these numbers are only to be used as rules of thumb as there are a huge number of factors which will influence motor life).
2. Brushes cause sparks and electrical noise within the motor.
3. The friction created by the brushes limits the top speed of the motor and can create heat issues.
4. As the electromagnets are on the stator it is easier to keep them cool through heat sinking or other cooling techniques.
5. Electromagnets being mounted on the stator also makes it easier to increase the accuracy of control within the motor because they can be mounted very precisely and accurately.
As you have probably worked out by now, it is impossible to turn a brushless motor without a brushless motor controller.
If you apply power to the motor in the same way that you might do with a brushed DC motor you simply lock one coil up and make the shaft very hard to turn.
At their simplest, these controllers can simply control the speed of the motor without any introducing optimidation or advanced control options.
However, controllers such as the ZDBL Series of Brushless Motor Controllers are designed to be optimised to the specification of each motor, as well as offering advanced programming options such as preset acceleration curves and startup programs.
Brushless motors are superior to brushed DC motors.
The removal of brushes from the design reduces friction, increase life, increases the top speed, increases the power density and enables much more accurate control.
It is for these reasons that many companies and engineers are now switching from brushed DC to brushless DC.
The one central disadvantage which is often highlighted is quite simply related to the cost which is higher than DC motors. However, depending on your application, the cost may be an issue but is always worth thinking about the lifespan of the product that you are building.
If a brushless motor and controller costs 3 times as much as a DC motor but lasts 5 times as long (and therefore requires less man hours, costs and hassle in parts replacing) then it is quite likely to deliver for money over its life.
If you have any questions about the cost effectiveness of brushless motors or would like support in sourcing the right motor for your application then please feel free to contact us by phone, online chat or email.
We will give impartial advice on the best system for your application even if it means you do not use any Zikodrive Motor Controllers.
In the same way that brushed DC motors are used in a huge range of applications, so too are brushless motors. The power density and efficiency of brushless motors is also making them increasingly popular in a range of other applications, particularly as environmental regulations and energy efficiency become more important in a range of industries.
Typical applications include pumps and process control applications, automotive, space and laboratory equipment. It is important to remember that brushless DC motors tend to be better at higher speeds than lower speeds (although, depending on the pole count of the motors it may be possible to achieve excellent lower speed performance.
On the opposite side of this discussion, single pole brushless DC motors are (more or less) the fastest rotating motors it is possible to use with speeds of 100000 rpm being perfectly achievable.
If you feel you understand the basic theory behind brushless motors but are keen to find out more about some of the issues which arise with using them in practice then you can visit our MOTOR CONTROL FREQUENTLY ASKED QUESTIONS page.
We are constantly expanding this section to try and deliver informative and useful articles on a range of motor control subjects and there is a specific section on brushless motors.
If you do not see the question that you are looking for included in this please do get in touch with us as we welcome submissions from customers and potential customers.
We will then look to answer your query and include it on the FAQs section as soon as we can.