Electric motors differ from each other not only in parameters, but also in the principle of operation. Each of them has a limited scope. Reliable and efficient operation of the mechanism, which includes the engine, is possible only if it is correctly selected.
Instructions
Step 1
If you need the ability to quickly change the speed, use a collector motor with a permanent magnet on the stator. In addition to the linear dependence of the rotational speed on the voltage supplied to the motor, it has a significant efficiency, and is also capable of changing the direction of rotation to the opposite when the polarity is reversed. However, you have to come to terms with the need to power the motor with direct current. However, with today's assortment of semiconductor rectifier bridges, this is not a problem.
Step 2
If the use of a rectifier is undesirable, and the ability to adjust the speed is necessary, use the so-called universal collector motor. An electromagnet is installed on its stator instead of a permanent magnet. Due to the series connection, the direction of the current in the stator changes synchronously with the direction of the current in the rotor. This means that when powered with DC, the motor will rotate in the same direction at any polarity. The direction of its rotation will not change even when powered by alternating current. Therefore, in order to force such a motor to spin in the other direction, it is necessary to change the polarity of either only the stator or only the rotor. A universal motor is good for everyone, except for one thing: the dependence of its speed on voltage is not linear.
Step 3
The motors described above require the use of consumables - the so-called brushes, which require replacement as they wear out (of course, when the power is off). Motors with an electronic switching unit allow this procedure to be avoided. Many of them behave like a permanent magnet collector, allowing linear speed control by varying the supply voltage. But their efficiency is lower, and they do not allow reverse polarity reversal.
Step 4
If increased reliability is required from the motor, and dimensions and efficiency do not matter, opt for an asynchronous motor. They are three-phase (designed to be powered from an appropriate network), two-phase (designed to be powered from a single-phase network with the inclusion of one of the windings through a capacitor) and single-phase (powered directly from a single-phase network). It is highly undesirable to use three-phase motors in the same way as two-phase motors, that is, to include them in a single-phase network using a capacitor. A high-quality and well-chosen asynchronous motor serves for decades, requiring only periodic lubrication.
Step 5
To select the electrical power of the motor, divide the required mechanical power on the shaft by the efficiency (expressed not as a percentage, but as a decimal fraction). Multiply the result by a safety factor of 1.5 - 2.
