johnwasser:
You might want to start by eliminating I and D (set kI and kD to 0.0). Put your robot on its side and hold a board near the wheels so that the distance sensors measure "level". Your wheels should stop. As you tip the board slightly the wheels should start driving toward the closer side. If that test doesn't work (wheels run while 'level' or run in the wrong direction while 'tilted') you need to correct your control system.
This works fine!
He "try" to keep the balance, but after one or two oscillations he falls... ( with only P, with PI, PD, PID... I tried a lot of values of kp, ki and kd but nothing, in any configuration)