In your instructible video, you get yours to turn 90 degrees left twice, turning it a total of 180 degrees or so. Then the 'right' command turns it right about 90 degrees. When it's instructed to move forward, it moves a good 2-3 feet.
Mine does not do this. I was so excited to get it working, that I didnt realize that it only turns about 90 degrees, then the servo does not move any further, unless told to move the opposite direction. Then when instructed to move forward, it only moves about 6 inches.
The servos you instructed us to purchase were the HS-311 analog servo for $8.99 a piece. But are you using a different servo in the video? Maybe the continuous that's an extra $20 a servo? Yours do not seem to be restricted to only 90 degrees movements...