pm dc motor selection conditions
Many engineers believe that low-voltage DC motors are what they find in tools and equipment. A conventional DC motor in which a winding is wound and a magnet is placed on the casing. This is usually the first motor we introduced in the science class at school.
DC motors are used in millions of drive systems; providing low-cost solutions for many commercial applications, powering applications ranging from toys to automotive rearview mirrors, the characteristics and advantages of DC motors tell us that they are cheap and large Mass production.
Perhaps the lesser known technique used on small DC motors is the rotorless design. These motors can be found in many devices that require high-speed servo performance, such as robots, X-ray drives, prosthetics, laboratory analysis equipment, thermal imaging, radar drives, and high-end recording platforms. Applications using DC motors benefit from high dynamic drive, linear speed and torque control with high power-to-size ratio (compact size).
The design is based on a coreless or ironless winding, the body is located below the windings, and the outer casing of the motor is a magnetic circuit, which makes the design very compact. The commutators and brushes of smaller DC motors are made of precious metals such as silver, gold, platinum or palladium. They have low friction and hardly produce magnetic interference. The starting voltage of the motor is very low, and for large motors, they often use a copper-graphite commutation system to handle higher currents. The advantage of this type of motor is that no magnetic field can be decomposed and their inertia is very low. These factors offer some significant advantages over traditional motors. Even at low speeds there is no cogging torque and smooth rotation, low vibration and low noise operation.
The linear speed/torque characteristic makes the DC motor speed and torque easy to control, and the magnetic field of the motor coil and stator is not affected by the saturation effect in the magnetic field. Many rotorless motors use rare earth magnets to maximize performance and size, motor windings have very low inertia, and the motor can accelerate and decelerate to full speed in milliseconds, providing very high speed performance.
Since there is no iron in the rotor, the DC motor has a low winding inductance, so the spark level between the brush and the commutator is lower than in a conventional motor. Arcs often produce electrical corrosion and shorten the life of DC motors, so DC motors can be many times longer than conventional wire-wound motors.
All in all, DC motors are superior in performance because they can operate at very low speeds because there is no cogging torque, providing low inertia, allowing for high acceleration rates. Considering that DC motors are suitable for more demanding applications, iron-free motors have higher dynamic performance, higher power-to-weight ratios and longer life than more familiar conventional DC motors. The efficiency and longevity of DC motors is a key selling point, but each application should be different and the selected motor must meet the requirements.
