2025

PWM: The Key to Controlling Small Servo Motors

Pulse - Width Modulation (PWM) controls small servo motors by adjusting duty cycles. Servos use PWM signals to position their shafts accurately, with feedback mechanisms ensuring precise control.

Author:

Shenzhen XQ-POWER Technology Co., LTD.

In the realm of electronic control systems, Pulse - Width Modulation (PWM) stands as a fundamental technique with wide - ranging applications, especially in the precise control of small servo motors. This article aims to elucidate what PWM is and how it facilitates the operation of small servo motors, offering a comprehensive understanding of this essential technology.

What is Pulse - Width Modulation (PWM)?

Pulse - Width Modulation is a method of encoding analog signal levels into digital signals by varying the duration, or "width," of rectangular pulses within a fixed frequency cycle. At its core, PWM operates based on two key parameters: frequency and duty cycle.

• Frequency: Refers to the number of pulses generated per second, measured in Hertz (Hz). For example, a PWM signal with a frequency of 50 Hz means 50 pulses are produced every second. In the context of servo motor control, common frequencies range from 50 Hz to 333 Hz.

• Duty Cycle: Expressed as a percentage, it represents the proportion of time the signal is in the "high" state (active) within one complete cycle. For instance, a 25% duty cycle indicates that the signal remains high for 25% of the cycle duration and low for the remaining 75%.

The beauty of PWM lies in its ability to simulate analog values using digital means. By adjusting the duty cycle, it can control the average power delivered to a load, such as a motor or a light - emitting diode (LED). This makes PWM highly efficient and versatile, as it can achieve smooth control without the need for complex analog circuits.

How Small Servo Motors are Controlled by PWM

Small servo motors are designed to rotate to specific angles with high precision, and PWM plays a crucial role in this process. A typical small servo motor consists of a DC motor, a gear reduction system, a position feedback mechanism (usually a potentiometer), and a control circuit.

1. Signal Reception

Small servo motors receive PWM signals as control inputs. These signals are usually generated by a microcontroller, such as an Arduino or Raspberry Pi. The standard PWM signal for servo control has a frequency of 50 Hz (a cycle duration of 20 milliseconds, or 20 ms), and the duty cycle determines the desired position of the servo's output shaft.

2. Duty Cycle - Angle Relationship

For most small servo motors, there is a specific mapping between the duty cycle of the PWM signal and the rotation angle of the output shaft:

• Neutral Position: A duty cycle of approximately 7.5% (1.5 ms high - time within a 20 ms cycle) corresponds to the neutral position, usually 90 degrees.

• Minimum Angle: A lower duty cycle, around 5% (1 ms high - time), typically rotates the servo to its minimum angle, often 0 degrees.

• Maximum Angle: A higher duty cycle, around 10% (2 ms high - time), moves the servo to its maximum angle, usually 180 degrees.

3. Control Process

• Initialization: When powered on, the servo motor's control circuit reads the incoming PWM signal and determines the initial duty cycle. Based on this, it positions the output shaft accordingly.

• Closed - Loop Operation: The potentiometer within the servo continuously monitors the actual position of the output shaft. If there is a difference between the desired position (determined by the PWM signal) and the actual position, the control circuit adjusts the power supplied to the DC motor. For example, if the PWM signal indicates a 10% duty cycle (corresponding to the maximum angle) but the potentiometer shows the shaft is only at 150 degrees, the circuit will increase the motor's speed until the 180 - degree position is reached.

• Fine - Tuning: To maintain the desired position precisely, the control circuit continuously samples the PWM signal and the feedback from the potentiometer, making real - time adjustments to counteract any disturbances or inaccuracies.

In conclusion, Pulse - Width Modulation provides a simple yet powerful way to control small servo motors with high precision. By manipulating the duty cycle of the PWM signal, engineers and hobbyists can accurately position servo motors for a wide range of applications, from robotic arms and remote - controlled vehicles to automated machinery and consumer electronics. As technology continues to advance, the importance of PWM in servo control and other areas of electronics will only grow.

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