This project is extremely easy and very rewarding. I hacked a regular cheap RC car to be able to easily access the wheels and motor. All you have to do is get any toy car and remove the top of it. Next find the pairs of wires for each of the motors on the circuit board (mine had two motors giving me 4 wires in total). Cut the wires as close as you can to the board and then strip the edge of each of them. Lastly plug them in to the appropriate motor plugs in the motor shield. (Look at this great tutorial http://www.instructables.com/id/Arduino-Motor-Shield-Tutorial). You need to put one motor wire to the A+ channel and the other motor wire to the A- channel, then control it through the tutorial above (they provide an example and sample code too). So now you have control of one motor of the car, to control others just repeat the process and there you go! Now you can give it commands in a sequence and have it run on its own (in autonomous mode). A sample sequence you could do it a three point turn! Send me a video of the coolest sequence your hacked arduino car can do. Enjoy!
The code was very very simple that almost anybody could write it. Here is my code http://gv-8.com/arduino/carcode.html. It simply drives forward for 2 seconds, brakes for a second and turns the wheels, lastly it drives in reverse. Very simple. Don’t change the constant ints at the top of the code because those numbers are built into the motor shield and this project will not work with modified numbers.
Just plug the positive ends of the motors to the positive A and B channels and the same for the negatives. Very simple. This is a great project that is very rewarding to accomplish and encouraging for beginnings. For the power switch, just connect a nine volt battery to a battery snap connector (you can get them at radioshack for cheap: http://www.radioshack.com/product/index.jsp?productId=2062219), plug the negative directly into the gnd of the motor shield. Next attach the red wire to one end of the switch, and connect the other end of the switch to the Vin plug on the motor shield. Now you have a switch! I recommend using a 9V battery as power. Remember that anything over 12V could ruin the board so be aware!