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Printable Coin Mech 0.2

by IWorkInPixels, published

Printable Coin Mech 0.2 by IWorkInPixels Sep 16, 2012
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For a long time now, I've wanted to make a DIY pop machine. Now that I have access to cheap and rapid prototyping, it's time to revisit that project, and see if I can print a coin mech and a mechanism to dispense cans of soda, and wire all that up with an arduino and put it inside a wooden box.

Toward that end, here's my first pass at a printable coin mech, based on this video:

If you want to hack with me, the repo is here:

1: Coin return. The cradles need to be on a hinge, and a coin return lever needs to open up the coin mech when pushed. This is especially important because if the mech rejects a slug, it will usually do so by getting stuck in the mech. We need a way for the next user to clear the mech, or this is a clear DoS attack vector. :)

2: Failsafe. If the machine is off, a lever which is normally held out of the way by an electromagnet should be released and push the coin mech open.

3: Switches. At the back of each coin chute should be a mounting point for a switch.

4: Storage. Each denomination of coin should fall into its own coin tube.

5: Rejection of objects larger than a quarter. At the very top of the mech, discs which are larger than a quarter should be automatically rejected. This may just be handled by making the coin slot to the outside of the machine just big enough to take a quarter.

6: Escrow. Not necessary, but it'd be nice if the coins that you have placed in the machine should be held in escrow until you dispense a soda, and returned to you if you press the coin return button.

UPDATE 9/16/12: IT VERKS!!!

I just got my first test rig printed, and (when I use pretend force instead of actual counterweights) it works! Now all I need to do is add some real counterweights and some switches and we should be in business!


1: Print one coin mech top, one coin mech bottom, and one set of coin mech cradles.

2: The cradles must be ordered in size from the biggest at the top of the mech to the smallest at the bottom, such that quarters catch at the top, nickels next, then pennies, then dimes.

3: Line up each hole and place a rod through the mech bottom, cradle and mech top. It will need to be just small enough that the cradle can spin freely. Hold it in place by whatever means necessary; this is just a test rig! Washers will probably be necessary.

4: The cradles need to have a small counterweight glued to the bottom of them, so that they will return to their starting position after the coin has fallen out of the cradle into the coin chute.

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The few coin mechanisms I've fiddled with all used the regular change instead of a physical escrow.  (incoming tops off change reserves before dropping in the box)  You're already counting the incoming, why add mechanical complexity?

Speaking as someone who once worked with lots of coin mechs, you are entirely on the right track and this is awesome.  The cheap mass-produced coin mechs I used were finicky as hell and needed replacing often.