Both brushed and brushless motors are DC motors, which convert electrical energy into mechanical energy through the interaction of magnetic fields.
A brushless motor, as the name suggests, is a motor that does not use brushes to convert electrical energy into mechanical work. Before understanding the term "brushless," it's best to first understand the function of brushes in a brushed motor.
Brushed Motors
Brushes (in a brushed motor) connect current to a set of coils. When energized, these coils generate a magnetic field. This magnetic field interacts with the stationary magnetic field of the stator magnet (the stationary part of the motor), causing the rotor to rotate at a certain angle. The brushes then energize the next set of coils, causing the rotor to continue rotating at a certain angle, creating a cyclical, rotating, mechanical cycle that produces rotational motion. The two ends of the coils are connected to a commutator. The commutator has copper plates for brush contact and conductivity. Each segment is insulated from the next. These segments are called "commutator segments".
The assembly consisting of the motor shaft, coils, and commutator is called the armature.
The magnetic field generated by the energized coils causes the motor rotor to rotate. Currents of opposite polarity will reverse the direction of rotation. Brushed motors do not require external electronic equipment; they only need a DC power supply. Changes in the polarity of the internal (rotor) coils cause the internal (rotor) to rotate.
-Brushed Motors
Brushed motor
Brushless Motors
Brushless motors do not have a mechanical connection to input current into the coils. Instead, a driver is needed to excite and switch the coils to generate a rotating magnetic field. Typically, the coils are wound in the stator, and magnets are mounted on the rotor. Changes in the polarity of the outer (stator) coils cause the inner (rotor) to rotate.
There are two common types of brushless stators: slotted stators and slotless stators. In a slotted stator, the conductor is wound around the teeth of the stator. When the coil is energized, the teeth provide mechanical stiffness to hold the coil in place. In a slotless stator, the conductor is wound into a coil. The coil is then flattened and formed into a cylinder. The spool (basket) is then painted or heated to activate the adhesive properties of the magnet. The only mechanical stiffness of a slotless stator is the adhesion to adjacent conductors.
There are no teeth to hold the electrical wires in place. The slotless configuration allows more copper wire to be accommodated per unit volume, thereby increasing power density (output power per unit volume).
What are the differences between brushed motors and brushless motors?
In a brushed motor, the stator is the outer magnet, and the rotor is the coil. A brushless motor is the opposite—the fixed magnetic field is the stator coil, and the rotor is a permanent magnet.
In both cases, the interaction of these fields generates torque, causing the rotor to rotate. As the rotor rotates, the current in the windings is switched or reversed to produce continuous rotation.
Brush commutation devices typically use brushes made of graphite, which are mounted on metal bars (commutators) connected to the rotor coils. As the rotor rotates, the brushes transfer current from one set of coils to another.
The brushless device achieves commutation by sending a signal from a shaft position sensor to an external winding switching circuit.
Typical speed
Brush systems perform best when operating continuously between 1,000 RPM and 10,000 RPM. Higher speeds are limited to a practical limit of 10,000 RPM due to the inherent characteristics of the brush-commutator interface. As the rotor accelerates, the brushes begin to float on the commutator, causing poor physical and electrical contact. Brushless motors, on the other hand, can typically operate at much higher speeds—they are limited only by the mechanical integrity of the rotor, speed-related losses, and the stability of the bearings used.
Noise generation
The noise of a brushed motor comes from the bearings, brushes, and rotor imbalance. In a brushless design, the noise generated by the brushes is eliminated, resulting in quieter operation.
Life expectancy
Generally, brushless motors have a longer lifespan than brushed motors. The main limiting features of brushed motors are their brushes and commutator. The typical lifespan of brushes is usually 2,000 to 5,000 operating hours, but this should not be considered a guarantee for all applications. Brushless units typically have a lifespan exceeding 10,000 hours, but this is generally limited by bearing life and environmental conditions.
cost
Often, the total lifecycle cost of two products can be the deciding factor. Brushless motors require electronic actuators, while brushed motors do not.
The additional cost of the electronic driver makes brushless motor systems more expensive than brushed motors. Both types require a power source. Brushed motors can operate directly from a power supply. Brushless motors require a driver powered by an electrical supply. In addition to the motor cost, ongoing maintenance costs should also be considered during the selection process.
The following chart provides further comparison between brushed motors and brushless motors:
Both brushed and brushless motor technologies are suitable for today's motion control market. The choice depends on how the factors mentioned above influence the designer's objectives. Ametek PITTMAN application engineers are experts in these design considerations, and you can contact us to assist you in your selection.
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