Servo PWM question

[btomko]

For all servos either digital or analog, does it matter what the actual voltage magnitude of the PWM signal is? For instance, is a pulse of 19 ms at 0v followed by a pulse of 1 ms at 3.3v the same thing as a pulse of 19 ms at 0v followed by a pulse of 1 ms at 5v. I'm not sure if servo's average the voltage you send it in the PWM signal or if the voltage just needs to be high enough to trigger a digital transistor inside.

[alexcmag]

Only the pulse width matters, and the pulses cannot be nearest then 15ms between each other.

3.3V or 5V will not make any difference.

Actually, most ESCs have an internal 3.3V or 3V regulator, so the pulses a real RX send to servo usually is not 5V.

[pmackenzie]

FWIW, a servo does not average the voltage of the incoming pulse.
When the pulse starts analog servos generate an internal pulse based on the value of pot connected to the output shaft. It "subtracts" the two pulses and stretches the difference pulse to power the motor.

Digital servos do essentially the same thing, but the digital "comparison and stretching" can be more sophisticated. (PID feedback loop)

Hope that helps.

Pat MacKenzie

[rich smith]

Alex, not sure why you say servos need 15ms low time. Most units which use AA51880 and YT2462 controllers (HXT500, HXT900, Vigor series, etc.) work fine at 4ms and lower frame rate.

Also note that voltage makes a big difference in speed.


Only the pulse width matters, and the pulses cannot be nearest then 15ms between each other.

3.3V or 5V will not make any difference.

Actually, most ESCs have an internal 3.3V or 3V regulator, so the pulses a real RX send to servo usually is not 5V.