I hooked this up in a few minutes in order to deliver a five volt power supply to the robot's audio amplifier. The source of power in this circuit is a 12 volt car battery. I used a voltage regulator rather than a resistor as an alternative to reducing the voltage from the car battery into an amount that the robot can use. A voltage regulator basically looks like a jumbo transistor. Voltage regulators can get hot when they are in use so I attached mine to a big heatsink that I had saved out of something I taken apart a while ago. I made fiberglass spacer to cover the voltage regulator's leads so that nothing would get shorted out. The voltage regulator that I used was marked 78M05A but any 7805 regulator will work just fine.
I also drew up a schematic that shows how to connect the 12V car battery to any 5V device.