Drupal 8, attach field collection to some entity. In this example to commerce product entity.

gistfile1.txt

use Drupal\commerce_product\Entity\Product;
use Drupal\field_collection\Entity\FieldCollectionItem;

$product = Product::load(34);

$fc_item = FieldCollectionItem::create([
  'field_name' => 'ENTITY_FIELD_COLLECTION_FIELD',
]);
$fc_item->set('field_horizontal_position', $horizontal_pos);
$fc_item->set('field_vertical_position', $vertical_pos);
$fc_item->setHostEntity($product, FALSE);
$product->ENTITY_FIELD_COLLECTION_FIELD[] = [
  'field_collection_item' => $fc_item,
];
$product->save();