Venduino Serves Snacks, Shows Vending is Tricky Business

Seems like just about every hackerspace eventually ends up with an old vending machine that gets hacked and modded to serve up parts, tools, and consumables. But why don’t more hackerspaces build their own vending machines from scratch? Because as [Ryan Bates] found out, building a DIY vending machine isn’t as easy as it looks.

[Ryan]’s “Venduino” has a lot of hackerspace standard components – laser-cut birch plywood case, Parallax continuous rotation servos, an LCD screen from an old Nokia phone, and of course an Arduino. The design is simple, but the devil is in the details. The machine makes no attempt to validate the coins going into it, the product augurs are not quite optimized to dispense reliably, and the whole machine can be cleaned out of product with a few quick shakes. Granted, [Ryan] isn’t trying to build a reliable money-making machine, but his travails only underscore the quality engineering behind modern vending machines. It might not seem like it when your Cheetos are dangling from the end of an auger, but think about how many successful transactions the real things process in an environment with a lot of variables.

Of course, every failure mode is just something to improve in the next version, but as it is this is still a neat project with some great ideas. If you’re more interested in the workings of commercial machines, check out our posts on listening in on vending machine comms or a Tweeting vending machine.

[via r/arduino]

19 thoughts on “Venduino Serves Snacks, Shows Vending is Tricky Business

  1. Why not replace the rotating spiral with a hydraulic piston and place the snacks on a slant to keep them in place, also why not try a weight sensor to get a better idea what coins are put in (sure slugs would still work) but all in all nice work.

    1. Pistons would work fine if there was only ever one item per row. When you start to get into multiple items per row the spirals not only move the item forward but keep other items equally spaced out and queued up. I have seen vending machine layouts that use little trap doors for every individual item. Tho they usually only have a representation of the item(s) in the machine on the front display and you never get to see what’s really going on inside.

    2. Pistons mean you have to have a lot of space for it to retract to and then you need a way to actuate it. Having an air compressor internally would not be the greatest and pneumatics like this are pretty hard to control for precise movement. Way too complex.

    1. What would be better?
      To me the augers seem fairly elegant and simple. You might be able to increase reliability slightly but it’s going to mean a more expensive machine that requires more maintenance.

    2. Why, the vast majority of vends are successful. Using the screws it mechanically simple and allow you to display the front of the product while keeping the item secured from people trying to tip the machine to get free product. It also allows a large variety of products from the same setup. Seems like a winning design in my opinion.

    1. I seriously considered a conveyor system however I just kept running into design issues that would add more complexity/points of failure to a machine that used them.

      Initially I considered them for something uniform like soda cans and the idea seems to work out fairly well. Except if you stored them standing upright which would be the most efficient way of packing the most into a machine. They would be prone to tip especially if someone where to shake the machine. You would almost be assured that they would get free product. You could certainly store them sideways, they would be less prone to roll out assuming you had special elevated segments to store them in place but it would be less efficient storage requiring larger machines.

      Which made me think about candy bars which are almost exclusively stored standing upright to maximize the amount the machine can hold in a minimum space. A conveyor could never accomplish that without a secondary system or some sort of clamping mechanism built into the belt. A secondary system is just another point of failure to eventually deal with and the clamping mechanism would likely make the belt itself more prone to failure over time. Which while great for the manufacturer of the belts would be less great for anyone who was thinking about buying into the Vending Machine business.

      Chips and other snacks that tend to flop over would end up being problematic when it came to storage density conveyor wise. Tho I suppose some sort of overhead mechanism that held them and released them as it moved into position would probably work. However you run into the fact that you are moving away from a system with exactly one moving part that dispenses whatever to a system with intricate mechanisms that all represent additional points of failure.

      Even the drop mechanisms have potentially hundreds of extra parts in the form of solenoids/latches for each level of product storage.

      The augers deal with storage density, product security, display and dispensing. they do it fairly well with a minimum number of failure points. They certainly aren’t perfect but they I’m personally hard pressed to figure a simple mechanism to replace them that covers everything they do that doesn’t have some catch that makes it problematic or expensive.

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