Hi, I have a problem with my servo (SG90). It doesn't work when I connect it to external power source. I have 4 AA batteries in series, positive end connected to red wire of the servo, negative end to brown one (=black). Also negative end of batteries to Arduino GND pin. And Arduino PWM pin (9) connected to orange wire (=white) of the servo. When I set it up like this, the servo keeps trying to move to position 0 (or even further in that direction - like to a -10 or something). But when connected to 5V from Arduino, works normally. Thanks for help
You should never attempt to power a servo or motor from the 5V pin of the Arduino -- this can damage the Arduino or cause it to reset.
The battery connection should work as you describe, if the batteries are fresh. Are they?
I would try adding some capacitors in parallel with the batteries. Remember that there is digital circuitry “inside” the servo. It seems to me that the current pulled by the motor may be causing the battery voltage to drop.