[Thad House]

Do you have the wheels mechanically mounted correctly? When looking from the top, the rollers should look like an X across the robot.

Also, unless gearing is different for each side, one side of the drive should be reversed, and one side should be normal. This should allow rotation correctly.

One way I like to check things is look at the lights on the motor controllers.

When going straight, 2 should be red, and 2 should be green.
When rotating, all 4 should be either red or green, depending on which direction you are rotating.
When strafing, 2 of the corners should be red, and the other 2 corners should be green.

1 More thing to check. When driving at a 45 degree angle, only 2 of the motors should be spinning, and they should be the 2 perpendicular to the direction you want to move. If thats not working correctly, then its most likely that either motor reversing isnt right, or the PWM ports are wrong.