Servo motors freaking out.

So i've got a MeArm hooked up to my Arduino that uses 4 of these servo motors, when I hook one motor up to Arduino's 5 volts it runs completely fine and when I hook up all 4 to four AA 1.5V batteries they also run fine.

But when only use 1 to 3 of servo motors to plugged into my AA batteries they act very strange, they either don't work at all or spin back and forth wildly or twitch quite a bit.

I assume this has something to do with the current but I've not been able to find much at all about this online and even less and how to correct it.

(I've also checked the volts with a voltmeter and they seem fine.)

Servos need an amp each, you should never power motors of servos from a logic 5V supply unless
you don't mind the risk of frying all your electronics.

Separate servo supply of 6V or so, rated for 4A or so. Servos and motors take shed-loads of power
compared to microcontrollers!!

It doesn't make much sense that 4 servos would be fine but less wouldn't work. My guess is that the wiring is bad somewhere. Can you post an accurate circuit diagram showing exactly what is connected where?

The servos should be powered directly from the battery NOT through the Arduino.

Steve

slipstick:
It doesn't make much sense that 4 servos would be fine but less wouldn't work. My guess is that the wiring is bad somewhere.

OP did you accidentally have the grounds disconnected in one case compared to the others?