Problem with rest api

  <?php

  // Use Loader() to autoload our model
  $loader = new \Phalcon\Loader();

  $loader->registerDirs(array(
      __DIR__ . '/models/'
  ))->register();

  $di = new \Phalcon\DI\FactoryDefault();

  //Set up the database service
  $di->set('db', function(){
      return new \Phalcon\Db\Adapter\Pdo\Mysql(array(
          "host" => "localhost",
          "username" => "root",
          "password" => "xxxxxxx",
          "dbname" => "robotics"
      ));
  });

  //Create and bind the DI to the application
  $app = new \Phalcon\Mvc\Micro($di);

  //Retrieves all robots
  $app->get('/api/robots', function() use ($app) {

      $phql = "SELECT * FROM Robots ORDER BY name";
      $robots = $app->modelsManager->executeQuery($phql);

      $data = array();
      foreach ($robots as $robot) {
          $data[] = array(
              'id' => $robot->id,
              'name' => $robot->name,
          );
      }

      echo json_encode($data);
  });
  $app->handle();

Hello Guys why i take 500 internal error? I have a Db Robots with table robotics and values id,name,type,year The problem is the $app->modelsManager->executeQuery($phql);

    Phalcon\\DI\\Injectable::__get(): Access to undefined property Phalcon\\Mvc\\Micro::Robots in       /var/www/html/restphalcon/index.php on line 30

Why doesn't work? Can someone tell me?

Thanks