Control continuous servo motor with Raspberry Pi and Python

Question

I am trying to control my continuous servo motor using this code:

import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
p = GPIO.PWM(17, 50)
p.start(7.5)
try:
        while True:
                p.ChangeDutyCycle(7.5)
                time.sleep(1)
                p.ChangeDutyCycle(12.5)
                time.sleep(1)
                p.ChangeDutyCycle(2.5)
                time.sleep(1)

except KeyboardInterrupt:
        GPIO.cleanup()

Servo operates correctly as the code sometimes and other it works randomly for the same code. I use another power source for the motor.

I don't think motor is damaged because I use Arduino to control the servo and it works perfectly.

JeffUK · Accepted Answer · 2017-07-17 19:20:15Z

1

If by 'works randomly' you mean 'it moves to roughly the right place, but wobbles around a lot' then the problem will be with the Raspberry Pi's Software Pulse-width Modulation (PWM)

The servo needs a consistent pulse to behave consistently, more accurate than the Pi's software can provide. So the pulse is slightly inconsistent which manifests itself in a 'jitter' (in a continuous servo this would be a random change of speed around the correct speed)

answered Jul 17, 2017 at 19:20

JeffUK

4,2912 gold badges22 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

TomServo · Accepted Answer · 2017-07-18 01:47:19Z

0

In addition to @JeffUK's answer above -- and I know it's not a software thing, but still germain -- is make sure your servo (even though you say it's powered by another source) and the Pi share a common ground connection. A floating ground can cause all sorts of unpredictable behaviors. It's very common for us software folks to forget that :) little detail when hooking up external devices.

answered Jul 18, 2017 at 1:47

TomServo

7,4895 gold badges34 silver badges52 bronze badges

1 Comment

Mohamed Gad Over a year ago

Thanks. I solved problem by using gpio.cleanup() in every loop I use.

Collectives™ on Stack Overflow

Control continuous servo motor with Raspberry Pi and Python

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related