Help me make a hopper and dispenser that won't clog and won't jam
February 10, 2015 9:01 AM   Subscribe

I need to make a hopper leading down to an opening. Below the opening will be a wheel. Food will fall into the wheel from the hopper. The wheel will turn, causing the food to drop below. Essentially, this but smaller. I'm having two problems with the wheel and hopper design: clogging and jamming. Help me figure out how to shape the hopper and wheel openings to prevent these problems.

This hopper and wheel will dispense treats, not food, so it can't throw out a giant cup full. Ideally it would dispense 1 or 2, but that's probably impossible, so I can mix the treats with regular food and let it dispense more, but still not a giant cupful.

Here is a picture of the current hopper. The assembled hopper and wheel. The inside of the wheel. The assembled dispenser. And the obligatory pictures of the beneficiary.

It's not necessarily clear in the picture, but the current food compartiment in the wheel is a wedge 1/3 the wheel size with the front tip (i.e. centre of the wheel) part partially blocked off so it it's not as deep. I have also tried a wheel with a smaller compartment and top edges that were rounded slopes, thinking that would let food slide upwards to prevent jamming (it didn't). This wider design mostly prevents jamming, as long as the wheel doesn't turn too far (which it doesn't need to).

The two problems:
1. Clogging: The treats/food find a stable position within the hopper and stop falling into the wheel.
2. Jamming: A piece of food that falls in sticks up a little higher than the wheel rim, and then when the wheel turns, it hits the side of the hopper and the wheel can't turn (the piece of food is against the right most side of the hopper and the left most side of the wheel.

Based on the video that I linked, the solution to number 2 seems to be to not allow the wheel to turn to the point where the left edge of the wheel compartment reaches the right side of the hopper. Ok, that's doable.

But what do I do about the clogging? One solution would obviously be to make the hopper mouth wider, but a) it's already dispensing a pretty large number of treats, so even with food I think this is enough and b) I think this would just make the food spill everywhere rather than into the wheel.

Options I've considered:
A) Vibrating the hopper after each treat dispensing. I did a test and the vibration isn't enough to unclog the hopper.
B) Putting some kind of 'stirrer" into the hopper to move after each treat dispensing. Problem: I don't know how this would work. Also, I wonder if the stirrer isn't just one more place for the food to balance against and clog.
C) Even smaller treats. I have pretty tiny treats. I tried cutting them in half, but this did not prevent the clogging.

I assume the answer is about A) The shape of the hopper opening B) The shape of the compartment inside the wheel. This affects how far the wheel has to turn before the treats will fall and how many treats will be held.

Is there a food hopper engineer out there?

The current depth, probably 3/4 inch is fixed by other constraints.
posted by If only I had a penguin... to Grab Bag (12 answers total)
I can't help you with the mechanics of this but Super Feeder makes a product for this. Their product has a number of settings to allow you to dispense the proper amount of food based on its size and also how long the "drum" runs for. The drum pushes the food out and a vibrating wire keeps the food from getting clogged. Neat design that has kept my cat happy for years. You might find some videos on the product to inform your design.
posted by firetruckred at 9:10 AM on February 10, 2015

I have been thinking about something similar (for pills, because I am too lazy to open them up every day and count them out) and the solution I was focussing on was a spiral of decreasing inner diameter rather than a simple angled chute at the bottom of the hopper. That way the weight of the treat/pill will align the item so that when it falls out the hole in the end it will be vertical, which allows for a more discrete vend (ie one at a time maybe). As they drop down, the spiral would twist them and with steep enough sides could funnel the volume down without Bob Marley getting involved (jamming).

So I think it's more in the shape of the 'sorting' of the treat to the wheel that is what is needed. One point of research there.

Another one is that the wheel opening/volume can be bigger than the dispensing opening/volume, which will mean that the wheel should have enough space for the treats to be knocked firmly into the void so it can rotate. They will have room to fall and drop on their side and not jam the opening, theoretically.

So in the video example instead of an open 1/4 circle with 1/4 of the diameter missing that ends up completely full, have an open 1/4 circle in the wheel but only open up the centre 1/4 to 1/3 of the diameter to the hopper. (so both sides of the open dispensing quarter has a 'roof' over it). Then the open 1/4 is only maybe 1/3 full and is less likely to jam.

Does that make sense? The size of the orifice dictates the rate of delivery but you don't need to match the size of the delivery and the rotating device as that is where your clogs are coming - because the rotating device is full when it doesn't need to be.
posted by Brockles at 9:24 AM on February 10, 2015

If you're not married to the hopper idea here's another thought: what is the form factor of the treats? If they can be stacked into a tube with a diameter of approximately 1 treat you might be able to position the tube at an upward slant (open at the top, with a cover of some sort to prevent theft) and add a motor-driven plunger that can push out exactly one treat at a time when you run the motor through the correct number of rotations.
posted by contraption at 9:26 AM on February 10, 2015 [1 favorite]

I've been thinking about this same problem recently.

Would it be an acceptable compromise to have a bunch of sections a human would load rather than a gravity feed? So your wheel could have 25 sections and get loaded by hand, making it a task that you'd only have to do every 25 periods?

One or two small things seems really hard. Especially when pet treats aren't as uniformly spherical as gum balls, nor do they have a smoothish surface.
posted by advicepig at 9:29 AM on February 10, 2015

I will need to re-read Brockles a few times to get it, but at the risk of threadsitting, I want to clarify that the opening in the wheel is already larger than the opening at the bottom of the hopper.

Also, the clogging is happening in the hopper, not in the wheel. So at some point, nothing falls from the hopper into the wheel. That part may already have been clear.
posted by If only I had a penguin... at 9:30 AM on February 10, 2015

To prevent clogging I'd try making the hopper asymmetrical, so that one wall is vertical or even very slightly sloped away from the center. That should make it a lot harder for the feed to form stable arches that span the opening and support the clogs.
posted by flabdablet at 9:31 AM on February 10, 2015

In the hopper? What if the wheel had a tickler, like a flexible wire or tab that would flick up into the hopper?
posted by advicepig at 9:34 AM on February 10, 2015

If the clog is in the hopper, then slippery sides and more vertical walls (to a smaller point) may work.

Is the clog at the top or the bottom? I'd suspect the angle you have now for the upper half of the hopper and a steeper angle at the actual dispensing point would work. You'd lose some treat volume but the reduction in drag from the sides may work.
posted by Brockles at 9:46 AM on February 10, 2015

You could abandon the wheel altogether and build a belt fed kibble dredge instead:
|             / @    _ 
|            @\@@@@ /
|           @@ -----
|          @@ /     \ @@  
|         \--|   *   |--\@
|           @|\     /|
|          @@| ----- |    @
|          @@|       |@
|         \--|       |--\
|           @|       |
|@@@@@@@@@@@@| ^     |
|@@@@@@@@@@@@| |     |@    @
|@@@@@@@@@\--| |     |--\
|@@@@@@@@@@@@|       |
|@@@@@@@@@@@@|       |
|@@@@@@@@@@@@|       |@
|@@@@@@@@@\--|       |--\
|@@@@@@@@@@@@|       |
|@@@@@@@@@@@@|       |
|@@@@@@@@@@@@|       |@
|@@@@@@@@@\--|       |--\
\@@@@@@@@@@@@|     | |
 \@@@@@@@@@@@|     | |
  \@@@@@@@@@@|     V |@
   \@@@@@@\--|       |--\
    \@@@@@@@@|       |
     \@@@@@@@|       |
      \@@@@@@|       |@
       \@@\--|       |--\
        \@@  |       |
         |  @|       |
         | @@|       |@
         |\--|       |--\
         |   |       |
         /   | ----- |
             |/     \|@    
          \--|   *   |--\
              \     /
             _/     \  @

posted by flabdablet at 10:28 AM on February 10, 2015 [4 favorites]

Essentially, scale this down.
posted by flabdablet at 11:13 AM on February 10, 2015

Maybe using something like this or the Lego equivalent?
posted by flabdablet at 11:43 AM on February 10, 2015

Tilting the dredge belt/chain would allow the use of simpler blades on the belt and unload more cleanly:
\                              |@@@   /
 \                             |@@@@ /
  \                          @@ >---< @
   \                      @@@@@/     \
    \@@@@@@@@@@@@@@@@@@@@@@\@@/   *   ) @
     \@@@@@@@@@@@@@@@@@@@@@@\/ \     /\
      \@@@@@@@@@@@@@@@@@@@@@/   ----/  \ @
       \@@@@@@@@@@@@@@@@\@@/       /
        \@@@@@@@@@@@@@@@@\/       /\      @
         \@@@@@@@@@@@@@@@/       /  \
          \@@@@@@@@@@\@@/       /
           \@@@@@@@@@@\/       /\          @
            \@@@@@@@@@/       /  \
             \@@@@\@@/       /
              \@@@@\/       /\
              /@@@@/       /  \            @
             / \@@/       /
            /   \/       /\
           /    /       /  \
            \  /----   /
             \/     \ /\                   @
             (   *   /  \
              \     /
              /     |
             /      |
With a suitable choice of blade width and height, you might even be able to achieve the desired one-at-a-time dispensing. Powering it with a stepper motor should give you good control.
posted by flabdablet at 9:59 PM on February 10, 2015

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