'the power comes up via the pulley here , and the cams move the swaging arms - that 's these things - and the combing gate , which is operated by the reciprocating mechanism , comes down just as the gripping shutter drops in this slot here , and of course at the same time the two brass balls go round and round and the flatting sheets carry off the straw while the grain drops with the aid of gravity down the riffling screw and into the hopper .