Shaking servos

Hello!
I’am using 6 servos on robot arm and they are controlled by SoftwareServo library on Arduino Diecimila. When I run 1-2 servos everything works fine, bet when I start to use more then 3 servos all the time some of them starts to “shake”, like they have to turn from 80-90 but they turn 80-100-90. What can be the problem?

library - http://www.arduino.cc/playground/ComponentLib/Servo

How are you powering the servos?

Yeah, for all servos 5V and GND from Arduino. This can be the problem?

yes that is overcurrent drain. Use a bigger battery and don't power arduino with the same battery of servos

I can use a 30V power source or I have to seperate every 5V to each servo? And the GND can be for all servos one from Arduino or they have to be seperated too?

And the GND can be for all servos one from Arduino or they have to be seperated too?

Grounds have to be common. You can power all the servos from the same rail providing it can supply the current.

I can use a 30V power source or I have to seperate every 5V to each servo

I don’t think I like your reasoning here - the servos are in parallel, so you need a single 5V supply capable of supplying enough current for all the servos.
DON’T try putting them in series with a 30V supply, apart from anything else, it would make common grounds…tricky.

AWOL, thanks, but why then I can't use Arduino 5V option? If you say then I have to put 5V for all 6 servos, then where is difference?

why then I can't use Arduino 5V option

Because the Arduino can't provide enough current. If you're running the Arduino off a USB, then the USB is limited to 500mA, which may well not be enough to run even a single servo.

Oh, I see, but that's kind a shity. On board writes 5V but actually less...

On board writes 5V but actually less...

No the voltage IS 5v it is just that the current is limited (like all power supplies) in this case to 500mA. The board will always write out the supply voltage but that can be dragged down by devices taking more current than it can supply.

I see, but that's kind a shity

Welcome to the real world.

OK, I went to the market and get 9V battery. I connect it with all servos, I tryed to use transistor to lower V till 5 and even connect all 9V to servos, but nothing did not work. This time it's not "shaking" but just don't work. The current are in servos, but it looks like it's not enough. Some recommendations where the problem could be?

I went to the market and get 9V battery

Do you mean one of those little ones about 3cm x 5cm x 2cm - aka "PP3"? Why did you do that?

Just have a look around the forum, and read what people think about these things. Useful for powering 1970s transistor radios, utterly useless for powering anything that moves.

For 6 servos, you should probably be looking at four C or D cells.

If I understand correctly than I have to put, for example, four D cell batteries together and then connect them to servos? And how long they work?

Your question is unanswerable without knowing how often you intend to move the servos, and what sort of loads they are under. It's like asking "how long will a tank of diesel last?" Two or three days, if I don't drive anywhere, but keep the engine running, but only a few hours if I drive everywhere at 160kph.

The best D types are rated up to 14Ah (yes, you read that right), but only at low discharge rates.

Ohh, I'am so ashamed than I have to say why. When I connect 4 D batteries to servos, the current were there but the problem was same, and I try to figure out more than 2h where is the problem since I remember about grounds, and that was so lame than I forgot to connect extra power GND to Arduino GND. Now it seems it's working, I hope so. Thanks everyone who help me. :)

Ohh, I'am so ashamed than I have to say why.

No reason to be ashamed of making making mistakes, only of you don't fix them. And thank you for letting us know, it might help the next one with the same problem.

Korman