[EricH]

To expand further, what you're seeing is known as a 6WD drop center drivetrain. The center wheel is dropped for easier turning; effectively the robot's wheelbase is cut in half. Incidentally, this is THE most common general drivetrain setup in FRC, at least the last 5-10 years or so. (8WD drop center is close.)

Here's an exercise if you're interested: Drive the robot without the middle wheels being installed at all. Then drive it with the middle wheels. You should see a difference.

Now, how to cope with the drop/rock: You'll probably want to put all your heavy items on one end. This would be the battery, the high-pressure side of the pneumatic system, and some if not all of the control system. That should hold that end down, giving the robot more stability.