Two years ago i delivered some hay to a feed store and a guy was unloading a load of small squares. He had a self unloading trailer which he made himself. He took two cylinders off a f-11 loader and mounted them under the bed. He ran two pieces of metal the length of the trailer that had groves in them tha was attached to a rack on the front of the trailer. When he worked the cylinders back and forth he pulled that rack all the way back and pushed the bales of the trailer. The metal that had groves in it held the rack in place when he worked the cylinders back and forth. The hay laid of the trailer into a nice stack. Kind of hard to explain excatly how it worked should of had a camera that day.