These pieces are called "ghost blocks" and can be achieved by attaching a motor on a movable block, whether its a slider, another motor, or a draggable. Any blocks attached to the motor will be able to pass through any metal pieces attached to the movable block. Attaching a draggable to (or using one as) the movable block will prevent the motor from spinning on its own. Here are examples of two basic ghost block setups: Spoiler: Ghost Block
My only guess is that the whole thing is connected by one large metal frame and so that frane be rotated
