Servo acts erratic with external power, why?

Other Hardware General Electronics
1

Hello,

My servo will act as expected if supplied by the Arduino 5V (I know you don't do this)
But will act erratically when supplied by a battery.

This servo was working properly from battery supply in past, not sure what changed.
I read about making sure the ground is right, pretty sure I got that though.

Wiring when supplied by Arduino:

pin1
pin11063×719 103 KB

Wiring when supplied by 7.4V Li-Po 20c:

pin2
pin21055×656 130 KB

Test Code

#include <Servo.h>

Servo myservo;

void setup()
{ 
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
  delay(2000);
  myservo.write(90); 
}

void loop() {

  myservo.write(90);
  delay(2000);
  myservo.write(80);
  delay(2000);
  myservo.write(100);
  delay(2000);
  myservo.write(90);
  delay(2000);

  while(1);


}

The battery does supply a voltage above the servo rating but the same thing happens with a 4xAA supply. Plus this servo has run fine on this battery in the past, even with more wiring though a breadboard.

The erratic behavior can be different but often it starts rapidly swinging the servo back and forth.
It will then start clicking as if it is making very small adjustments.

Servo: TM-8120MG Digital Servo - Wiki
Arduino: (Clone) Elegoo Mega 2560 R3
Battery: 7.4v Li-Po 20c

Any Ideas?

Thank you.

2

If you know you don’t do this why are you doing it :thinking:

Never ever never ever power a motor from the 5 volt Arduino pin.

If you insist in doing this, you will damage the device connected to the USB connector OR burn out the board regulator when you power the Arduino from the power connector.

7.4v might be too much for the servo. :face_with_spiral_eyes:

The servo circuitry is probably damaged.

3

The wires connecting the servo to the Arduino look suspect too.

1 Like
4

Just used 5V to debug my problem, didn't imagine that program could cause any problems.
Maybe you are right, my LiPo says 7.4v on it but is reading at 8.4v

5

How so? They just came in an electronics kit.

6

According to the servo wiki, the maximum operating voltage is 7.2V.

Most likely, either the servo has been damaged, or the battery cannot supply enough current.

If you "know" that you should never try to power a servo from the Arduino 5V output, but do so anyway, you can expect damaged equipment to be the rule, rather than the exception.

1 Like
7

At this point the best thing is to post your annotated schematic, frizzies do not give enough information and are NOT schematics. Also post links to technical information on each of the hardware devices. While you are waiting on our response you might consider ordering a new set of hardware and the appropriate poser supplies. You now have first hand knowledge why: A Power supply the Arduino is NOT!".

8

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