I need to make my arduino moving like a car, so I looked for a motor shield and I found this: http://arduino.cc/en/Main/ArduinoMotorShieldR3, but I've seen that it can control only two motors and I have to control four wheels. I've seen that cars work with one motor and something (I'm not an expert of cars, so I apologize for any mistake I do) that makes the wheels moving without having four motors. How can I reproduce this on my arduino? Can I mount more shields on my arduino (for example a motor shield and an ethernet one)?
Last question: how can I make my arduino turn? For example: if I say it to go forward, then turn left and then go forward, how can I make the wheels turn?
Thanks a lot!