Motors are a critical part of electric RC. When it comes to electric motors there are two kinds: Brushed and Brushless. What are the differences? Why would you upgrade? What do you need to support either type?
The obvious difference between the two motors is their use of brushes. The brushed motor works in the way that most of us know of how motors works from grade 10 science class. Generally, the armature or wire coils on the motor shaft act as electromagnets when a current is passed through them. The motor is configured such that there are permanent magnets around the armature that make use of the electromagnet fields produced to rotate the motor. The wire coils are attached to a commutator assembly on the armature which acts as a connection point for current transfer. The commutator is what makes physical contact with the brushes. So, since the armature is rotating, the commutator assembly and brushes are needed to transfer electricity to the coils for creating the magnetic fields. This mechanical contact will eventually ware down the commutator and brushes and require maintenance.
Brushless motors perform the same function but are built in a different configuration. The biggest difference being that the armature is fixed and it is the permanent magnets that are rotating. This means the permanent magnets are part of the motor shaft. With the armature fixed, there is no need for the commutator assembly and brushes or the maintenance involved. Brushless motors also are more efficient since there is no loss due to the mechanical nature of brushes. However, to get this configuration to work requires more complicated control electronics.
- Cheaper to produce/ purchase
- Simpler to control
Brushless Motor Pros
- Higher efficiencies
- Much less maintenance
With the mechanical contacts between the commutator and brushes of brushed motors there are sparks or arcs created each time the brush makes contact with a different part of the commutator. This arching causes electromagnetic interference (EMI) that may interfere with the vehicle’s transmitter/receiver resulting in ‘glitching’. To reduce the EMI generated brushed motors require the installation of filter capacitors. Brushless motors do not require these capacitors.
A specific type of Electronic Speed Control (ESC) is needed depending on what type of motor is being used. There are some Brushless ESCs that can bet set to run brushed motors but a brushed motor specific ESC will not operate a brushless motor. Generally it is simpler to control a brushed motor. In the past there were mechanical ESC that used high power resistors to reduce voltage going to the motor.
In brushed motors the commutator/ brushes are also used to ensure the motor rotates in the correct direction. In brushless motors another method is required to ensure the motor rotates in the correct direction. What is needed is a way to determine the position of the motor shaft. Knowing this position the ESC can send power to the correct coils for proper rotation. Different methods are used for this determination depending on the motor type.
Brushless motors are either Sensored or Sensorless. Sensored motors use a hall effect sensor to determine the motor shaft position. Sensorless motors use the back EMF on the unpowered coils to determine position. Some people experience ‘cogging’ with sensorless motors at low speed since the sensorless method for determining position is not as accurate as the sensored method.
Brushless set ups are part of some stock trucks these days but if they are not, upgrades to a brushless setup is sought after due to the benefits of the brushless system. If you are looking to upgrade keep in mind that it is a system change – you will need to replace the ESC and motor. The biggest drawback to upgrading to brushless is the cost. But the benefit of lower maintenance and longer life may even things out in the long run.