Hi there, I have a single 3v servo being controlled by arduino UNO and a pir sensor. I have tried a 9v and ruined the control mechanism on one of my servos. I have since realised this was not a good approach. I am now running the entire UNO and servo using 4 AA batteries. If I leave this on for an extended period could I end up with the same problem? Or should this be okay?
Thanks!!!!
6 volts is the minimum voltage to operate the Arduino alone, and you plan to use an Arduino UNO, a PIR sensor and a servo, all on 4 AA batteries? It might work but for how long? A hour, maybe less, who knows.
Right, I did test it and it was working very well for 2 hours.. ( i did not test it longer because of my concern with damaging another servo)
I am not concerned with the length of time it will last but rather that it will not damage my servo.
Do you see any potential problems aside from length of time 'on' ??
thank you 
You are powering a 3V servo with 6 volts, so that might be a problem. You may need to get a 3.3 volt regulator, just for the servos.
You could use three big diodes in series to drop the voltage to the servo from ~6v to ~3.9v.
You could use three big diodes in series to drop the voltage to the servo from ~6v to ~3.9v.
It's a cheap-and-dirty solution, but I'll admit I've done something like that.* But I don't feel good about it! 
The problem is, that you are regulating the voltage drop (and not regulating it very well) instead of regulating the voltage supply to the servo. So as the battery voltage drops over time, the servo voltage will also drop. And as a percentage drop, the servo drop is worse!!! When the battery voltage drops by 1V (from 6V to 5V), that's a 17% voltage reduction. But with an approximately-constant 3V drop across the diodes and the batteries down to 5V, you'll only have 2V remaining for the servo. That's a 33% voltage reduction to the servo.
So, you end-up with something that's the opposite of a voltage regulator! The output-voltage has more variation than the input-voltage (as a percentage).
If you have a single 3v servo that doesn't draw too much power and an R3 Uno, I imagine you could use the 3.3v pin on the Arduino to power the servo.
But with an approximately-constant 3V drop across the diodes
Most of the common diodes I use have a ~.7v drop (~2.1v drop for 3 in series, 6v - 2.1v = 3.9v). What kind of diodes you use?
DDRYA:
3v servo
That's an unusual servo. What is the supported supply voltage range? Do you have a link to the spec?
I imagine you could use the 3.3v pin on the Arduino to power the servo.
50mA wouldn't run an average mobile phone's vibra motor, much less a servo.
I suggest you don't try it.
This is the usual problem when trying to run the Arduino and servos at the same time.
In general, it's best to power the servos from a different supply than the Arduino board,
although it's inconvenient for only 1 servo.
There's really no good way to do it. Besides, the series diodes idea, for just one servo,
the easiest way might be to use an extra voltage regulator, running off a common
battery.
I've never heard of a 3V servo, most are rated at 4.8-6V. OTOH, on all of my robots,
I use Hitec servos, and run them at 7.2V [ie, 6 NiMH AA-cells in series], and this hasn't
seemed to be a problem. I would never power them from 9V, however. I use LDO
regulators on the Arduino boards, so they can handle Power in down to 6V, so servos
and board all run off the same 7.2V batteries.
I've never heard of a 3V servo
Well here's one....
That's not a "3V" servo, it's a 6V servo that will still continue to work all the way down to 3V, so you don't
really want to put 3V on it like the other guys were mentioning, you want to put the normal voltage
voltage on it.
oric_dan:
That's not a "3V" servo, it's a 6V servo that will still continue to work all the way down
to 3V.
Oh