Input: the lower green shaft to which a gear and a roller are fixed. The roller contacts with the orange strip through a rectangular hole in the blue runway.
The upper green shaft fixed with a gear and an incompleted roller rotates in a bearing that can slide in a vertical slot of the yellow base.
The friction forces at contact places between the strip and the rollers are created by the red spring. The strip is advanced periodically due to the incompleted circle profile of the upper roller..