Explainers
Motor Types
Cored vs Coreless vs Brushless. Choose the right motor for your application.
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Cored
A cored, brushed DC motor is the most popular variety of servo motor due to its cost effectiveness. The armature windings for the motor are wound around an iron core (hence the name) which doubles as a heat sink. Due to their construction they have higher torque at starting/slow speeds and speed control over a wide range of voltages. These features make cored servo motors suitable for applications requiring steady, high torque and reliability.
Their downside is they have a lower electrical efficiency (approximately 50%) and have higher maintenance requirements due to wearing brushes. Additionally, they have higher inertia, which can slow down response times and make them less ideal for applications needing rapid acceleration and deceleration.
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Coreless
Coreless motors, also brushed DC motors, do not have an iron core. Instead the armature windings form a self-supporting hollow cylinder (hence "coreless"). This smaller, lightweight and compact design drastically reduces rotor inertia, allowing for high acceleration and deceleration rates. Although coreless servo motors tend to offer lower torque compared to their cored counterparts, their linear speed/torque characterestics allow for easier, more rapid and precise motion control at varying speeds. Additionally, they have a high electrical efficiency (approximately 90%) and have longer life due to the reduced electro-erosion. They also tend to have low noise and reduced vibration.
Their construction combined with the use of rare earth magnets, such as Neodymium, make them more expensive than their cored counterparts. Additionally, without the iron core to serve as a heat sink they do not handle thermal overloads. They also require additional electronics. -
Brushless
Unlike brushed motors (which are mechanically driven) brushless DC ("BLDC") motors are electronically driven. Instead of brushes, an electronic controller creates a three-phase variable current that powers the motor's coils in succession which yields a superb 1μs dead band width. This results in exceptional responsiveness, accuracy and centering.
Their design results in a longer life and reduced maintenance requirements, making them better suited to continuous or long-running duty cycles. They also have much higher electromagnetic efficiency. These factors make them versatile for a wide range of applications, including high-performance RC helicopters, airplanes and cars, UAVs and complex industrial automation systems.
3-Pole vs 5-Pole
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3-Pole Motors
3-Pole motors are characterised by having three magnetic poles on the rotor. This basic configuration is commonly found in simpler, more economical electric motors. The primary advantage of a 3-pole motor is its simplicity and cost-effectiveness, making it a popular choice for low to moderate demand applications where precise control and high efficiency are not critical. However, the trade-off for this simplicity is less smooth operation and lower torque efficiency compared to motors with more poles. The fewer number of poles means that these motors might have a higher speed but can exhibit more cogging (the tendency of the motor to jerk between poles), which can affect the smoothness of the motor's rotation, especially at low speeds.
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5-Pole Motors
5-Pole motors feature five magnetic poles on the rotor, offering smoother operation and greater torque efficiency than motors with fewer poles, such as the 3-pole motors. The increased number of poles allows for more gradual transitions between magnetic fields as the rotor spins, which reduces cogging and results in smoother and more precise motor performance. This makes 5-pole motors more suitable for applications requiring finer control and smoother operation, such as in model trains, high-quality electric fans, and precision instruments. The additional poles also contribute to improved starting torque and can enhance the motor's ability to maintain consistent torque under load, albeit typically at a higher cost and complexity than motors with fewer poles.
