Brushless and Brushed, What’s the Difference?
The principle behind brushless and brushed motors is very similar. When an electric current is passed through the windings of the motor, magnets distributed within the motor are attracted or repelled. The repetitive repulsion and attraction of the magnets translates into a revolution of the shaft. This allows the motor to spin an attached propeller at extremely high speeds, in turn, producing thrust.
Brushed FPV Drone Motor
The internal operation of a brushed motor is contrary to that of a brushless FPV drone motor. In the brushed motor, the stator provides a permanent magnetic field that surrounds the rotor. The rotor of the brushed motor is an electromagnet which is influenced by the surrounding stator. A pair of brushes attached to DC power contact the commutator ring at the base of the rotor. The commutator ring is divided, therefore its rotation will periodically reverse the direction of the current flowing through the rotor, as its rotation causes the commutator to reverse its polarity. The alternation of the commutator ring polarity translates into uninterrupted revolution of the rotor.
This entire process occurs internally within a motor can, which provides excellent protection for the delicate components. Although, efficiency of the system is reduced due to the greater thermal insulation of the internal mechanics. It is possible to reverse the rotation direction of the motor by inverting the polarity of the DC power input. Due to the contact of the brushes with the commutator, longevity of the brushed motor is greatly reduced in comparison to the brushless motor. In terms of application, a brushed motor is better suited for micro class multicopters, their small size, low weight and simple driving technique improves their suitability for micro FPV flight.
Brushless FPV Drone Motor
As the name implies, a brushless FPV drone motor lack brushes. The brushless motor can be effectively divided into two separate components; the rotor and the stator. The stator is the central unit into which the rotor is mounted. The stator is made up of a network of radial electromagnets that alternatively power on and off to produce a temporary magnetic field when a current is passed through the windings. The rotor holds a collection of permanent magnets which are positioned in close proximity to the semi-permanent stator electromagnets. Attractive and repulsive interaction of the stator and rotor magnets is translated into rotational movement. When assembled, the shaft of the rotor is inserted into a pair of ball bearings located in the stator that maintain linear, smooth revolution of the rotor.
Although the brushless motor is powered by DC current, it can’t be driven directly. Instead, the brushless motor is wired to the control electronics, effectively eliminating the need for brushes or a commutator. Longevity of the brushless motor is excellent as there is no physical contact between the rotor and the stator. The brushless motor is also more efficient than the brushed motor. The brushless motor is extensively used in mini and some micro multicopter applications, where high power outputs and efficiency are prioritized.
Motor Sizing and Identification
The size of a brushless motor is identified by a four-digit code that details the dimensions of the stator in millimeters, for example: 2206. The first two numbers in the series determine the diameter of the stator, in this case, 22mm. The final two describe the height of the stator, the last two numbers in this series are “06” therefore the stator unit is 6mm tall. It is important to remember that these numbers do not describe the external dimensions of the brushless motor itself.
The size of a brushed motor can be identified through a simpler two number system that clearly defines the diameter and height of the exterior can in millimetres. Example: 6×15, the first number “6” is a measurement of the cans diameter and “15” the height of the can.