Step 3: How it Works: Receiver
You can see in the code that every time the Arduino successfully recognizes the start code, it blinks the LED that comes pre-installed on pin 13. This makes it easy to see it your radio is transmitting properly -- the white light should be flickering on pretty much continuously.
The Arduino scales the motor values to be higher the further the potentiometer is from 128, with a maximum amplitude at 0 and 255 (raw values). The direction (reverse / forward) is determined by the two digital inputs that go into the H-bridges ( the motor driver circuits -- I used the design from Mark Tilden's site). Pull one side high, it goes reverse, and the other side makes it go forward. That might sound mysterious, but look at the schematic with all the transistors laid out nicely and it'll make sense. The H-bridges I built can be seen in the picture.
Anyway, the motors draw a relatively large amount of current, so you can't power them directly from the 7805 -- they draw from the 7.4V battery through transistors. The servo and radio, however, do run off the voltage regulator. You can see all of the receiver parts connected together above. It is a bit of a mess, in the name of reducing weight.