Thinkster MEAN Stack Factory

I was going through the Thinkster.io MEAN Stack tutorial and had a question about why my implementation doesn't work. I know this isn't what is exactly being asked but was wondering how you would make this work. I wanted to use the factory to show my posts that I moved into my factory from the controller. The code is shown below for app.js.

`

var app = angular.module('flapperNews', []);

app.factory('posts', [function(){
var o = {posts:[{title: 'post 1', upvotes: 5}, {title: 'post 2', upvotes: 2},  {title: 'post 3', upvotes: 15}, {title: 'post 4', upvotes: 9},{title: 'post 5', upvotes: 4}];
};
return o;
}]);

app.controller('MainCtrl', ['$scope', 'posts',function($scope, posts){
  $scope.test = 'Hello world!';
  $scope.posts = posts.posts; 
  $scope.addPost = function(){
    if(!$scope.title || $scope.title === ''){
     return; 
    }
    $scope.posts.push({title: $scope.title, link: $scope.link, upvotes: 0}); 
    $scope.title = '';
    $scope.link = '';
    };
  $scope.incrementUpvotes = function(post){
    post.upvotes += 1; 
  };

}]);

`

Originally the object of posts in the factory was in the controller as $scope.posts. Now it is in the factory (being referenced as posts.posts) and does not display. How would you make the array display in the html, as I have {{post.title}} under a main controller div with ng-repeat that works prior to the factory being introduced.