That is all handled inside the ESC with it's BEC (battery eliminator circuit), it takes the 2 cell Li-po voltage and internally regulates it to 5vdc for the esc controller AND outputs +5vdc to the red wire on the 3 pin servo connector. So just wire the servo connector to the arduino (ground pin, +5vdc pin, and digital output pin) and your done.
Aha, thank you very much ! First time working with ESC's with an Arduino so, thanks for your help
Is there any way to give my arduino more than 5 analog input ports btw? Or do I have to get the Arduino Mega then.. Need only 8 analog inputs