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Published 2026-04-10
This guide explains the precise method to calculate the PWM signal period for a standardservomotor. For almost all hobby and industrial RCservomotors, the PWM signal period is fixed at20 milliseconds (ms), which corresponds to a frequency of50 Hertz (Hz). The key takeaway: the period is constant; only the pulse width within that period changes to control theservo's position.
The PWM (Pulse Width Modulation) signal period is the total time for one complete on-off cycle. It is the inverse of the signal frequency.
Formula:
Period (seconds) = 1 / Frequency (Hz)
For standard servo motors, the operating frequency is almost universally50 Hz.
Calculation:
Period = 1 / 50 Hz = 0.02 seconds = 20 milliseconds (ms)
Therefore, the PWM signal period for a standard servo motor is 20 ms.
Within this fixed 20 ms period, the servo position is determined by thehigh pulse width(the "on" time). The remaining time in the period is the low pulse (the "off" time). This is a critical distinction: you never change the period; you change the pulse width.
Note: Always verify your specific servo's datasheet, as some models may use 0.7 ms to 2.3 ms or other ranges.
While 50 Hz is the standard, some digital servos or continuous rotation servos may accept other frequencies (e.g., 100 Hz, 200 Hz, or 333 Hz). Use the same formula.
Step 1: Identify the target frequency (F) in Hz.
Step 2: Apply the formula: Period (seconds) = 1 / F.
Step 3: Convert seconds to milliseconds: multiply by 1000.
Example: For a servo specified to work at 200 Hz.
Period = 1 / 200 Hz = 0.005 seconds = 5 ms
Critical Warning: Do not exceed the servo's maximum rated frequency. Using a shorter period (higher frequency) than specified can cause overheating, jitter, or permanent damage. For 99% of standard RC servos,stick to 50 Hz (20 ms period) .
To ensure your PWM signal period is correct, take these concrete steps:
The servo's manufacturer datasheet is the only authoritative source. Look for the "PWM Period" or "Control Frequency" specification. If not listed, assume 50 Hz (20 ms).
Measure the actual PWM signal from your controller (e.g., microcontroller, servo driver). Set the time base to 10 ms/division. You should see a repeating cycle of exactly 20 ms. Measure the high pulse width separately to verify it matches your desired angle.
If your servo's pulse range is from my_pulse (e.g., 0.5 ms for 0°) to max_pulse (e.g., 2.5 ms for 180°), use linear interpolation:
Pulse_width = min_pulse + (angle / max_angle) (max_pulse - min_pulse)
Example for 45° on a 180° servo (0.5 ms to 2.5 ms):
Pulse_width = 0.5 + (45 / 180) (2.5 - 0.5) = 0.5 + 0.25 * 2.0 = 1.0 ms
Do not change the period to adjust angle. Always keep period constant (20 ms for standard servos).
Do not use a frequency below 40 Hz (period > 25 ms) – this can cause the servo to lose holding torque and become erratic.
Do not assume all servos use 1.5 ms as center. Some digital servos use 1.52 ms or other values. Verify.
The PWM signal period for a standard servo motor is fixed at 20 milliseconds, derived from the 50 Hz control frequency. You calculate the period as 1 divided by the frequency. For reliable operation, always keep the period constant and only modulate the high pulse width to control position. Before deploying any servo, verify its specific pulse width range and frequency tolerance from the official datasheet. Use an oscilloscope to confirm your signal matches the required 20 ms period. This approach ensures precise, stable, and damage-free servo control.
Update Time：2026-04-10
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