Delete One or More Items in MongoDB ?

How do I delete one or more items from MongoDB ?

I've tried this and its not working =(

    $robots = Robots::find([['name'=>'test']]);
    foreach ($robots as $robot) {
        $robot->delete();
    }

I get "Error: Call to a member function notifyEvent() on array" in "Library/Phalcon/Mvc/MongoCollection.php (469)"