The 4-pole design is more robust than the 2-pole equivalent, but can also take up the same space and weight. Greg Dutfield from maxon UK explains.
4-pole motors have advantages in choosing micro DC motors for applications ranging from aerospace to well drilling control. The 4-pole design is more robust than the 2-pole equivalent, but can also take up the same space and weight. Greg Dutfield from maxon UK explains.
For DC motors requiring high torque with low weight and compactness, a 4-pole motor may be the best choice. 4-pole motors may take up the same footprint as 2-pole motors, but they are capable of generating more torque. It is important to note that a 4-pole motor is also stronger than a 2-pole motor of comparable size, meaning that it maintains its speed more accurately when a load is applied.
The number of poles refers to the number of pairs of permanent magnets in the motor. A two-pole motor has a pair of magnets opposite north and south. When a current is applied between the pairs of poles, a magnetic field is created, causing the rotor to rotate. Motor configurations also range from 4-pole, including two pairs of poles, to multi-pole designs, including up to 12 poles.
The number of poles is an important aspect of motor design as it affects the speed and torque characteristics of the motor. The lower the number of poles, the higher the speed of the motor. This is because each mechanical rotation of the rotor depends on the completion of the magnetic field cycle for each pair of poles. The more pairs of permanent magnets a motor has, the more excitation cycles are required, which means that the longer it takes the rotor to complete a 360° rotation. The speed is divided by the number of pole pairs at a fixed frequency, so assuming a 2-pole motor at 10,000 rpm, a 4-pole motor will produce 5000 rpm, a six-pole motor will run at 3300 rpm, etc. d. .
Larger motors can generate more torque regardless of the number of poles. However, increasing the number of poles can generate more torque than a motor of the same size. In the case of a 4-pole motor, its torque is greatly increased by its compact design with a thinner magnetic return path leaving more space for two pairs of permanent magnet poles, and in the case of maxon motors, its patented thicker braided winding.
Although a 4-pole motor may take up the same footprint as a 2-pole design, it should be noted that the further increase in the number of poles from 6 to 12 means that the size and weight of the frame must be commensurately increased to accommodate the additional copper cable. , iron and magnets are not required.
The strength of a motor is usually determined by its speed-torque gradient, meaning that a more powerful motor can hold speed more tightly when a load is applied. The speed-torque gradient is measured by the decrease in speed per 1 mNm of load. Lower numbers and gentler grades mean the engine will be better able to maintain its speed under load.
A more powerful motor is possible thanks to the same design features that also help it achieve higher torques, such as more windings and the use of optimal materials in the manufacturing process. Thus a 4-pole motor is more reliable than a 2-pole motor of the same size.
For example, a 4-pole maxon motor with a diameter of 22 mm has a speed and torque gradient of 19.4 rpm/mNm, which means it only loses 19.4 rpm for every 1 mNm applied, while a 2- a maxon pole motor of the same size has a speed and torque gradient of 110 rpm. /mNm . Not all motor manufacturers meet maxon’s design and material requirements, so alternative brands of 2-pole motors may have higher speed and torque gradients, indicating a weaker motor.
Aerospace applications benefit from the increased strength and light weight of 4-pole motors. These attributes are also needed for hand-held power tools, which often require more torque than a 2-pole motor can provide, yet are light in weight and small in size.
The performance of the 4-pole motor is also important for mobile robot manufacturers. Wheeled or tracked robots must overcome rough terrain, obstacles and steep slopes when inspecting oil and gas pipelines or searching for victims of an earthquake. 4-pole motors provide the torque and power needed to overcome these loads, helping mobile robot manufacturers build compact and lightweight designs.
The small size, combined with low speed and torque gradients, is also critical to well control in the oil and gas industry. For this application, compact 2-pole motors are not powerful enough and multi-pole motors are too large for the bit inspection space, so Maxon developed a 32mm 4-pole motor.
Many applications suitable for 4-pole motors occur in extreme environments or in conditions that require the ability to operate at high temperature, high pressure and vibration. For example, well control motors can operate at temperatures in excess of 200°C, while motors installed in autonomous underwater vehicles (AUVs) are housed in pressurized oil-filled tanks. With additional design features such as sleeves and technologies to improve heat dissipation, the compact 4-pole motors can withstand extreme operating conditions for extended periods of time.
While motor specifications are fundamental, the design of the entire drive system, including gearbox, encoder, drive and controls, should be considered to optimize the application. In addition to consulting on motor specifications, maxon engineers can also work with OEM development teams to develop application-specific complete drive systems.
maxon is a leading supplier of high precision brushed and brushless DC servo motors and drives. These motors range in size from 4mm to 90mm and are available up to 500W. We integrate motor, gear and DC motor controls into highly accurate intelligent drive systems that can be customized to meet the specific needs of our customers’ applications.
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