Presumably, everyone is not unfamiliar with servo motors, especially those who play with model aircraft. Servo motors play an important role in model aircraft, especially fixed - wing model aircraft and model ships. The turning, takeoff, and landing of an aircraft rely on the servo motor to control the positive and reverse rotation of the ailerons. This requires the traction of the servo motor.

Servo motors are also known as micro servo motors. The structure of a servo motor is relatively simple. Generally speaking, it consists of a small DC motor (small motor), a set of reduction gears, a potentiometer (connected to the gear reducer and acting as a position sensor), and a control circuit board (usually including a voltage comparator, input signal, and power supply).

Different from the principle of a stepper motor, a servo motor is essentially a system composed of a DC motor and various components. A stepper motor rotates to a specified position by applying an electrical pulse to the stator coil to generate a magnetic field, which attracts the permanent - magnet rotor or acts on the reluctance - core stator. Essentially, the error is very small, and there is generally no feedback control. The power of a servo motor, this kind of micro servo motor, comes from a DC motor, so there must be a controller that sends commands to the DC motor, and there is feedback control in the servo - motor system.

The output gear of the reduction gear set inside the servo motor is essentially connected to a potentiometer to form a position sensor. Therefore, the rotation angle of this servo motor is affected by the rotation angle of the potentiometer. The two ends of this potentiometer are connected to the positive and negative poles of the input power supply, and the sliding end is connected to the rotating shaft. As the sliding piece rotates with the rotating shaft, the voltage between the sliding - piece end of the potentiometer and the negative [sensitive word] of the power supply changes with the rotation of the rotating shaft. This voltage and the control signal are input into a voltage comparator (operational amplifier), and the power - supply terminal of the operational amplifier is connected to the input power supply. The input control signal belongs to a Pulse - Width Modulation (PWM) signal, which changes the average voltage by varying the proportion of high voltage within a certain period. This is input into the voltage comparator.

By comparing the average voltage of the input signal with the voltage of the power - position sensor, for example, if the input voltage is higher than the voltage of the position sensor, the amplifier outputs a positive power - supply voltage. If the input voltage is lower than the voltage of the position sensor, the amplifier outputs a negative power - supply voltage, that is, a reverse voltage. Thus, the forward and reverse rotation of the DC motor is controlled, and then the rotation of the servo motor is controlled through the output reduction gear set, just like in the figure above. If the potentiometer is not coupled and bound to the output gear shaft, it can be coupled to other shafts of the reduction gear set. By controlling the gear ratio, a larger - range rotation of the servo motor, such as 360°, can be achieved. And this may cause a larger error, but there will be no cumulative error (i.e., the error does not increase with the increase of the rotation angle).

Due to their simple structure and low cost, servo motors are applied in many places, not limited to model aircraft. They are also used in various robotic arms, robots, or automatic doors. They can achieve various mechanical movements. In fields with high - precision requirements or those that need high torque and large loads, there are special high - torque and high - precision servo motors available. The size of the servo motor is determined by the outfitting according to the classification society's standards. When selecting a servo motor, the torque size is the main consideration. How to carefully select an economical and suitable servo motor is also a knowledge that cannot be ignored.