Knowledge
Home > Knowledge > Content
Why the speed of digital servos is faster than that of analog servos?
- May 31, 2018 -

Many die friends mistakenly believe that: "The digital servo's PWM drive frequency 300Hz is six times higher than the analog servo's 50Hz, and the servo motor speed is six times faster, so the digital servo's response speed is six times faster than the analog servo'." . Here we need to pay attention to the concept of duty cycle, the pulse width is the effective level time per cycle, and the duty cycle is the percentage of the pulse width/cycle, so the size is independent of the frequency. The duty cycle determines the voltage applied to the motor. When the load torque is constant, the motor speed is determined, independent of the PWM frequency.

Analog servo is a DC servo motor controller chip generally can only receive 50Hz frequency (period 20ms) ~ 300Hz PWM external control signal, too high frequency will not work. If the PWM external control signal is 50Hz, the resolution time of the position information obtained by the controller chip of the DC servo motor is 20ms, and the difference between the voltage of the proportional PWM control signal and the voltage of the feedback potentiometer is obtained, and the difference is expanded by the pulse width. The air-to-air ratio is changed, and the size is proportional to the difference.) The drive motor is then actuated. This means that due to the frequency limitation of the PWM external control signal, a new adjustment of the servo rocker arm position can be made in the fastest 20 ms.

The digital servo can receive the PWM external control signal much faster than the 50Hz frequency (period of 20ms) through the MCU, and the position information of the PWM external control signal can be distinguished in a shorter time, and the voltage proportional to the duty ratio of the PWM signal is calculated. The difference between the voltage of the feedback potentiometer and the voltage of the feedback potentiometer is used to drive the motor to perform the latest adjustment of the position of the rocker arm of the servo.

Conclusion: Regardless of analog or digital servos, when the load torque is constant, the motor speed depends on the duty ratio of the drive signal and is independent of the frequency. The digital servo can receive higher frequency PWM external control signals, obtain position information after a shorter cycle time, and make latest adjustments to the position of the servo rocker arm. Therefore, the speed response of the digital servo is faster than that of the analog servo, rather than the speed of the drive motor is faster than that of the analog servo.