For our project we need to sort three different marbles they are all the same same but one is made of glass, wood, and metal. So we are wanting to use a weight sensor to tell the difference. However we don’t know how to make one any advice or suggestions. Thank you so much anything would help.
maybe a shaft in an encoder with a rubber band under tension around it on the concept of one of these.
image from commons.wikimedia.org/wiki/File/Spring_scale_-_3241.jpg
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If they truly weight differently you may be able to build a ramp system where the floor gives out via pendulum that can balance out the different weights. The heaviest would fall first, then the second heaviest under the next section. If the marble makes it to the end then it was the lightest. each section should have a bucket to collect under the 2 trap doors and the ending ‘exit’.
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Sorry, that link to the original source is broken. I legally (copyright terms) have to tell you that it’s actually from File:Spring scale - 3241.jpg - Wikimedia Commons and licensed under Creative Commons Share Alike from the Wikimedia user Amada44. Also, that post is now under Creative Commons Share Alike 4.0
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what about a color sensor instead? all three of those materials are different colors, so it could work. You could make the marbles go down the same track, but with a color sensor near the bottom. Depending on the color/material, you could make a latch open for that color/material, and then close when another one is being sorted. You could also have a stopper that stops all the other marbles and makes it so only one marble is sorted at a time.
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This may be a bit complicated but you could modify it to work (I had to upload it as a .zip because its a slideshow)
Class3.zip (500 KB)
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Also, building on the previous ideas, to use marble weight, color, or light reflective properties to differentiate their materials you can use the following trick:
Instead of comparing marble weight to pre-tensioned spring or rubber band and, instead of reading absolute light or color sensor value, you can compare each incoming marble to the marbles in the sample set of all materials.
For example, if you have two identical light sensors one reading sample marble and another incoming marble (or one sensor scanning both marbles in sequence) then it should work more reliably under any external lighting conditions.
Similarly, you could build a little balance scale for each marble in the sample set that will compare the weight of incoming marble to the sample. Then it could either trigger a switch or let them get sorted by purely mechanically activated trap doors like @SCFarrell suggested.
On the other hand, properly tuned sorter with its own light source is fun to watch too:
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My group is working on our marble sorting project where our machine needs to be able to sort 15 marbles of three different compositions wood, glass, and metal. They are all the same size and we need to have two sensors currently we only have a light sensor. We want to also have a way to see if the marble conducts electricity however we need help on how to build and code this so it can tell whether it is or is not a metal marble. We are using vexcode v5 for this project. Any thing will help like advice or suggestions. Thank you so much.