void FixedUpdate()
{
float moveHorizontal = Input.GetAxis ("Horizontal");
float moveVertical = Input.GetAxis ("Vertical");
Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);
rigidbody.velocity = movement * speed;
rigidbody.position = new Vector3
(
Mathf.Clamp (rigidbody.position.x, boundary.xMin, boundary.xMax),
0.0f,
Mathf.Clamp (rigidbody.position.z, boundary.zMin, boundary.zMax)
);
rigidbody.rotation = Quaternion.Euler (0.0f, 0.0f, rigidbody.velocity.x * -tilt);
}