Servo doesn't move when powered externally

I have 4 servos.All of those are towerpro sg90 servos.When i tested all 4 by powering with external 5v input,i found that 3 of them respond to instructions but 1 of them doesn't move.But when i connect that servo to the arduino 5v output it works.Can someone help me with the problem? I am using arduino uno and using 4AA batteries as external input.

Make sure all the grounds are connected and use your multimeter to check continuity and proper power to the servos. 4AA batteries are not enough, if all servos will be moving at once.

If that is not the problem, please read and follow the directions in the "How to use this forum" post before reposting.

Note that you can damage the Arduino by trying to power motors and servos from the 5V output. It is not designed for that.

Four alkaline AA batteries will be over 6V when new. That’s not normally a problem but I wonder if that one servo is sensitive to overvoltage.

But a wiring problem is far more likely. You’re not connecting the servos via a breadboard are you? That can cause all sorts of problems.


Can someone help me with the problem?

The others have said how, but let me spell it out.
Connect the negative of you battery pack to the ground of the Arduino.

Here is why:-

with external 5v input

What does that mean ?
What 5v external input ?

Show us a good schematic of your circuit.
Show us a good image of your wiring.
Give links to components.
Posting images:

Does this have anything to do with this thread?

Tom… :slight_smile: