Automatic Tissue Dispenser

My father is a software engineer and yesterday he asked me a question to test me, that I cannot, for the life of me, seem to figure out. He told me that I need to make a tissue paper dispenser that, upon activation, would dispense tissue paper of only length 15cm. Now suppose I have a tissue roll of 7.5 cm with a hole in the center of the roll with a radius of 3 cm, height 15 cm and the thickness of one sheet of tissue being 0.1mm. The tissue paper roll would go onto a stand and that stand is controlled by the rotations of a motor fixed to it. Now you tell me, how would this machine of yours work. Would the rotation of the motor in order to dispense be angle of rotation dependent or would it be time dependent? How would you account for the continuously changing radius of the toilet paper? What would be the formula, rather, algorithm you would use for this rotation of the motor and the continual change of radius, considering you need some buffer length of tissue from the roll to the cutter?

• I'd be more concerned about how to stop the paper tearing then the loose end sticking to the roll messing with the feed. When I need toilet paper and none comes out, that is much worse than if 20cm comes out when it should be 15cm. Nov 25 '21 at 16:35