:o
arduino, duemilanove
when i plug the arduino into usb, the two continuous rotation servos (arduino controled) work fine according to my code (turn in oposite directions then switch directions)
but when i plug the arduino into my 6v power supply it dosent work...
i know the suggested voltage is 7v but usb runs on 5v...?
ALSO 9v dosent work too
Most problem having to do with driving multible servos have to do with the total current being drawn.
Servos should really have their own DC voltage applied from an external source rated at an amp or more per servo. Powering them from the +5vdc voltage from the Arduino board puts too much demand on the internal +5vdc regulator or the USB's thermal current fuse. The fact that your two servos work while on USB is more luck then anything. It depends on the size of the servos plus any mechanical load placed on them.
When using external DC power for servos or motors or anything else be sure to remember to wire the ground of the external source to the Arduino's ground.
Lefty
And do keep in mind,
alot of the times you can use lower voltages and higher voltages in motors and such for speed.. but in servos (and even some motors), you're just adding more stress with over/under powering than you would if you powered it right with a full load, having your servo burn out, or worse.. something on your board :X
When it's a recommended voltage, it's.. well, recommended that you use that voltage:D
The fact that your two servos work while on USB is more luck then anything.
I would guess that it's due to the PC's voltage regulation on the USB power source being better than the onboard voltage regulator, perhaps?
Wasn't there a thread just a few days ago where someone else was having the same problem - servos worked fine on USB power, but not on a wall wart? Might be worth looking up and seeing what that user's fix was.
Fixed it, wired the arduino to 9v batterie and servos to 6v (4 aa bats)
VIDEO COMMING SOON
on: http://www.aklem.com
thx guys 
just have to work out that calabration routine for my reflectance sensors...
The life of a 13 year old... (computer taken away lots)