Understanding Servo Angle Control: The Power of PWM
The Principle of Servo Angle Control
Servo motors are widely used in robotics, remote-controlled devices, and automation projects due to their precise angle control. At the heart of this precision lies PWM (Pulse Width Modulation), a simple yet powerful technique. In this section, we’ll break down how PWM enables accurate servo control.
Introduction to PWM Signals
PWM, or Pulse Width Modulation, is a square wave signal that conveys information by adjusting the duration of its high-level state, known as the pulse width. Here’s a closer look at its key aspects:
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Definition: PWM transmits data by varying the pulse width within a fixed period.
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Parameters:
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Period: 20ms (frequency of 50Hz, calculated as 1/20ms = 50Hz).
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Pulse Width Range: 0.5ms (0°) to 2.5ms (180°), with linear variation.
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Duty Cycle: The ratio of pulse width to period, e.g., 1.5ms / 20ms = 7.5%.
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Function:
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The servo’s control circuit maps pulse width to a target angle:
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0.5ms → 0°.
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1.5ms → 90° (neutral position).
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2.5ms → 180° (maximum angle).
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A 1μs change in pulse width corresponds to approximately 0.09° (180° / 2000μs).
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Example:
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An Arduino sending a 1ms pulse width results in a target angle of 45°. The control circuit adjusts the servo’s output shaft accordingly.
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Why Use PWM:
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It’s simple and easy to implement with microcontrollers.
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As a digital signal, it resists noise interference.
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It’s a standardized protocol across the servo industry.
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Detailed Principle and Implementation of PWM-Controlled Servos
PWM controls a servo’s rotation angle by adjusting the duty cycle of the signal. Let’s dive into the detailed principle and practical steps to implement it.
Principle of PWM-Controlled Servos
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PWM Period:
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The standard period is 20ms, equivalent to a 50Hz frequency (1 / 50 = 0.02 seconds = 20ms).
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Pulse Width Duration:
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Within the 20ms period, the high-level duration (pulse width) ranges from 0.5ms to 2.5ms, corresponding to 0° to 180° rotation.
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Examples:
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0.5ms pulse width → 0°.
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1.5ms pulse width → 90°.
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2.5ms pulse width → 180°.
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Duty Cycle:
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The angle is controlled by adjusting the duty cycle, calculated as (Pulse Width / Period) × 100%.
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Examples:
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0.5ms / 20ms = 2.5% (0°).
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1.5ms / 20ms = 7.5% (90°).
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2.5ms / 20ms = 12.5% (180°).
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Steps to Implement PWM Control
Follow these steps to control a servo using PWM:
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Generate PWM Signal:
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Use a microcontroller like Arduino or ESP32 to create a 20ms (50Hz) PWM signal.
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Set Pulse Width Duration:
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Calculate and set the pulse width based on the desired angle. For instance, 1.5ms for 90°.
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Output PWM Signal:
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Send the PWM signal to the servo via the signal line. The servo will rotate to the corresponding angle.
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Conclusion
PWM is a cornerstone of servo control, offering simplicity, precision, and reliability. Whether you’re a hobbyist building a robot or an engineer designing automation systems, mastering PWM opens up a world of possibilities. Ready to try it out? Grab your microcontroller and start experimenting!