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I'm new to electronics and have run into a problem while trying to hook up my micro-servo to my Pi.

I have a Rapsberry Pi model 3 B, a breadboard, a 6V power supply, and a TowerPro MG90S micro servo.

The way I have everything wired is as followed:

  • The battery supply is connected to the right side power rails, the black goes negative, the red to positive.

  • The micro servo gets connected with the black wire going to negative, middle wire (orange/red) to positive, and the yellow wire goes directly to pin 11 (6th row, first pin) on my pi.

  • Lastly, the ground pin on the pi (row 3, pin 2) is hooked up to negative on the right side of the power rail.

The code I'm using to test it I found online:

import RPi.GPIO as GPIO

import time

GPIO.setmode(GPIO.BOARD)

pin_number = 11
GPIO.setup(pin_number, GPIO.OUT)

frequency_hertz = 50
pwm = GPIO.PWM(pin_number, frequency_hertz)


left_position = 0.40
right_position = 2.5
middle_position = (right_position - left_position) / 2 + left_position


positionList = [left_position, middle_position, right_position, middle_position]


ms_per_cycle = 1000 / frequency_hertz

for i in range(3):
        for position in positionList:
                duty_cycle_percentage = position * 100 / ms_per_cycle
                print("Position: " + str(position))
                print("Duty Cycle: " + str(duty_cycle_percentage))
                print("")
                pwm.start(duty_cycle_percentage)
                time.sleep(.5)

pwm.stop()


GPIO.cleanup()

When I run this, nothing happens. I don't know if the pi is faulty, the servo is, or something might be wired incorrectly.

2
  • Try adding a transistor to the signal wire on the servo.
    – scitronboy
    Mar 27 '18 at 22:16
  • Please make a wiring diagram/schematic. Mar 28 '18 at 8:02
1

See https://pinout.xyz/ for the pin out of the Pi's 40-pin expansion header.

I'm assuming you have connected the servo control wire to GPIO 17. I'm further assuming you have connected a Pi ground to the servo ground.

To see if your servo works enter the following commands.

sudo pigpiod # start the pigpio daemon

pigs s 17 1000 # send 1000 micro pulses to servo
pigs s 17 1500 # send 1500 micro pulses to servo
pigs s 17 2000 # send 2000 micro pulses to servo
7
  • Yes, that all seems correct. It doesn't seem to respond to any of those commands. I almost wonder if the battery is not working correctly, but I don't have a volt meter to test it.
    – Astrum
    Mar 27 '18 at 21:38
  • Forget the battery. Power the servo from the Pi's 5V rail. That should supply more than enough for a 9g servo or two or three.
    – joan
    Mar 27 '18 at 21:42
  • Unfortunately that didn't work either. I rebooted my pi and tried again, no luck.
    – Astrum
    Mar 27 '18 at 21:58
  • You need to add a photo of your connections. There is very little to go wrong with a servo.
    – joan
    Mar 27 '18 at 22:00
  • 1
    @mrSidX There are two hardware PWM channels connected to GPIO 12/13/18/19 on the expansion header. pigs/pigpiod uses hardware timed PWM on any of GPIO 0-31 which is fine for servos/ESCs.
    – joan
    Mar 28 '18 at 7:13

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