void Update()
    {
        var state = gameObject.GetComponent <WeightEnemy>().CurrentState;
        var y     = (originalPosition_.y - transform.localPosition.y) / moveLengthY;

        // Forecast an enemy's y-position because of servo delay.
        if (state == WeightEnemy.State.FALLING)
        {
            y += (transform.localPosition.y - groundPosition_.y) * EnemyFallingForecast;
        }
        else if (state == WeightEnemy.State.RISING)
        {
            y -= EnemyRisingForecast;
        }
        servo_.SetY(y);
    }