There are many ways of powering the ArbotiX - this guide will discuss the two primary methods.
To change between power methods, you will need to change the power jumper. The power jumper pins are located next to the FTDI port, as shown below
Powering the ArbotiX via FTDI/USB
To power the ArbotiX via FTDI/USB, first set the power jumper to the FTDI setting. This will route power from ywour FTDI device (which usually draw 5v from your USB port). This method can be useful for development and testing. On problem with powering the ArbotiX this way is that you cannot power the Motor Controller, the Hobby servos, or the DYNAMIXEL servos from the FTDI port. To do that, you must power the ArbotiX from the Power Terminals
Powering the ArbotiX from the Power Terminals
The ArbotiX screw terminals are designed to work with a DC voltage between 6v and 24v. This voltage will be used for the motor controller, the Hobby Servo ports, and the DYNAMIXEL ports, so be careful to not plug a motor in if the voltage is too high for your attached devices. InterbotiX kits usually use 11.1V is powered via LiPo batteries and 12V if powered via a SMPS/wall power supply. This voltage is safe for the AX and MX DYNAMIXEL servos.
When the power jumper is switched to 'VIN', the ATMEGA644p chip will receiver power through the 5v regulator. This regulator can supply up to 1A of power for the ATMEGA644p and any input/output devices attached to the Analog, Digital and IIC ports. This also supplies power for the 5V communication signal used to communicate with the DYNAMIXEL servos.
See also LiPo Guide