My Geocrawler (A robot originally built on the VEX Robotics platform) uses a pair of constant rotation servos for moving the tracks.. I tried using the +5V from the Arduino, but the 5V regulator couldn't handle the load. I finally opted to direct wire the +V (center pins) of the servos from a 2ndary power source. (in this case, the 7.2V RC battery.) The signal wire can be driven directly from the Arduino without any problems, but the servos need to be a little more 'Umph!" As cr0sh said, they need to be at least 1-amp per servo.. and using the USB port might not do it, or worse, you could burn-out the internal fuse to the port if the servo draws too much. Most servos run between 5V to 8V. (Not sure I would try the 9.6V RC battery.. might be a little high. Not worth risking the electronics of the servo.)Hope this helps!