Let's Make Robots!

Problem with my first robot

Hello,

I have a problem with my first robot following firtsl's tutorial, i've done a robot like the part II of his course and i've put the same code. (http://letsmakerobots.com/node/254). It take sometimes to understand the code but finally i understood it.

You can see in the video that the comportment of the robot is not the one I expected. It seems to reverse the motor to many times and i don't why.