Arduino mini sumo robot

Updata 10/2/2014

Finally the Mcmaster University SUMO Robot competition ended, my robot got the third place. It is fun and an excellent experience.

Update 23/ 1/ 2014

now i have a new problem, when i plug in the usb to arduino UNO, the program is working as i expect, however, when i plug in the battery to ardunio instead of usb, my robot is not acting as it should. would anyone plz tell me why is this happening?

I'm a second year mechatronic student and im going to make a mini sumo robot for competition. i started with doing some research and modeling on inventor. At the beginning i decided to use ultrasonic sensor for detecting opponent and its working well, however it can't fit between front and rear wheel. so i come to SHARP IR sensor. now the problem is that i dont know how to progrm my robot to make it follow ant object appear in front of it. The video i linked is exactly what i want to achieve. Would anyone plz help me give me any hit or show me a sample arduino code?