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For a University project I have to build a small box containing ice cubes. The box is a shoe box, isolated with newspaper and aluminium foil, cooled by thermal packs. In this box I want to store ice cubes for about one to three hours.

Now comes the tricky part: The ice cubes should drop out of the box, one after another, about every minute.

I was thinking of a motor with an oval disk which opens a flap gate. The second idea was a small conveyor band which transports the cubes out. Are there better solutions than that? What minimum motor power do I need for this? How do I control the motor?

It's a low-budget project, so the cheapest solution is the best.

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  • \$\begingroup\$ Three hours at 1 cube a minute is 180 ice cubes. Figuring out how to squeeze them in a shoe box in a way that they are dispensable and not going to freeze together is going to be rather tricky. I think you need to figure out a plausible mechanical design before anything else. \$\endgroup\$ – Chris Stratton Dec 20 '10 at 21:04
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These are hard questions to answer, not because the information you need is hard to come by, but because answering them in a straightforward way will keep you from learning how to do it yourself, which is presumably why you're going to college in the first place. On the other hand, it reasonable to say, "Look, I don't know how to do this, and there is no point in trying to reinvent motor control from first principles."

So how about this for an answer that will get you started.

You're trying to do a task where the motor will need to spin a little bit, then stop and wait, then repeat. Also, overall, this is a pretty low power task-- you're not trying to move a car or train. For this kind of low-power, intermittent duty task, I'd probably start with a small stepper motor, like you find in old disk drives or printers. You could also use a small DC motor, like you find in most motorized toys, but you'll probably need some clever ratcheting mechanism to make the intermittent motion you're after.

In general, motor power is proportional to volume; you want a motor that is bigger than a grape and smaller than an apple.

The next step is to google "stepper motor" and "dc motor controller." I'm afraid Wikipedia will be incomprehensible at this stage; I'd look for tutorials from robotics clubs or intro electronics sites. You might start with:

After that, since you say this is a low-budget project, I'd try to find something with a motor in it that you can reuse-- maybe the mechanism from an inkjet printer (stepper motor) or an RC car (DC motor). You might be able to reuse something without taking it apart-- like maybe you could just have the printer print a page once a minute, and the motion would pull on a string that somehow moved the ice.

From there, draw a lot of pictures of what you want to build and try building some crappy prototypes out of cardboard, string, and paper. You'll learn faster by testing and failing than by trying to plan it all out in your head first.

Good luck.

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  • \$\begingroup\$ Thanks! I like the idea with the printer! I have a bunch of broken ink jets laying around, so finally I can reuse them. Maybe just mount the whole guide rail with the motor at the bottom of the box and use the motion with a string to open the flap gate. \$\endgroup\$ – Patrick Dec 18 '10 at 11:55
  • \$\begingroup\$ +Inf: "...answering them in a straightforward way will keep you from learning how to do it yourself, which is presumably why you're going to college in the first place." \$\endgroup\$ – tyblu Dec 18 '10 at 17:12
  • \$\begingroup\$ Nope, this is not why I go to college in first place as this part of the project has nothing to do with my major nor my minor. I just need to solve the problem. \$\endgroup\$ – Patrick Dec 19 '10 at 12:42
  • \$\begingroup\$ Interesting! If you don't mind explaining a little, what are you trying to do with the ice cubes? Some kind of science experiment? Something artistic? \$\endgroup\$ – pingswept Dec 19 '10 at 15:53
  • \$\begingroup\$ It's both - the result will be an artistic installation with all the other student projects. The installation is about the various states of water and the process while transforming from one to another. \$\endgroup\$ – Patrick Dec 19 '10 at 16:51
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I'm not sure how easy it is to come by, but I'd look for an old refrigerator with ice dispenser. All dispensing mechanisms I've seen are screws/augers that grab some ice and push it forwards to drop it down a hole into your drink. You may be able to modify the "intake" to grab one cube at a time, or if it's not that critical you get 1 cube/min, just use it stock.

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I believe that the ice maker in a refrigerator uses an auger-type delivery system. You could make something like that with copper tubing or something else that's malleable enough to bend into that shape. I'd use a stepper motor as suggested above and have a photosensor determine when a single ice cube has dropped and then open a door (if it absolutely has to be one-at-time).

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