Here is THE HOBBIT filmstrip, one of the last movies to run through the 35mm projector system. The plate under the film slowly sped up into first gear and then the clutch (in the middle) slipped into neutral. The film actually uncoiled from the inside out, and if you ever saw the whole system operating you would be spellbound.
Before the new digital projectors arrived, the gear system and motors for the plater was salvaged from old vacuum cleaners and parts of the plater clutch came out of an old Buick (so I was told).
