I had a student who I was teaching basic electronics who presented me with an interesting problem. She had a family tradition that every year at Thanksgiving there would be a jar of acorns and the family would play all submit guesses as to how many acorns were in the jar. It had always been the role of the family patriarch to count the acorns and determine the winner. The patriarch had gotten older and had some health issues that meant he could no longer be the counter of the acorns. However no one else in the family really wanted the job. So her solution was to ask me to build a robot that could not only count the acorns but make it look a whimsical while it did the job. After some discussion we had both settled on marble machines as inspiration which would ultimately lead to several a problem since acorns are not nearly as uniform as marbles.
##Electronics
The initial electronics consisted of an Arduino nano, a OLED screen, and a momentary switch with a wire to actuate it. I had hoped that just by putting the switch in the path of the acorns i could count them as they went by. Oh how naive I was. The switch was later replace with an IR beak beam sensor to count the acorns as they fell past the sensor into a collection hopper after they were slowed down and separated enough to ensure each break of the beam would only be a single acorn and not a whole group falling together.
##Marble Mechanisms We initially looked at this marble balance contraption which can count out a single marble at a time, but as I said already acorns are not marbles. They were too light and too inconsistently shaped to actuate the mechanism. But this did get the acorns rolling
##Screw
I decided that I needed to slow down and separate the marbles and taking some inspiration from industrial machinery I thought that a big screw would be a simple way to do that. I sectioned the tube that the marble were running through and added this screw to see if i could turn it by hand and move the marbles through. The basic idea worked.
There was a lot of adjustment to be made and the ultimate solution involved the screw being mounted on a pivot to adjust for the variable size of acorns. It still occasionally got stuck but if no acorns were counted after 5 seconds the motor would reverse the screw for a few seconds which usually cleared a jam. The acorns in the funnel still need to be agitated if they get stuck but that creates user interaction which is important for this family tradition. The machine is not intended to be 100% reliable and operating independently.
The machine has been successfully counting acorns at their family thanksgiving since 2021.