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Hopper jamming

  1. Dec 13, 2013 #1
    I'm making an automatic fish feeder. It uses a very low torque, low RPM, low energy motor to turn a paddle wheel. The paddle wheel pushes the food off a ledge and into the tank.

    I plan to make the paddle wheel using a gear. I also have access to a 3d printer to make the part.

    The motor is definately something I am going to use since it runs for a month on just a AA and I have it and I am not willing to mess with electronics.

    THE PROBLEM: Jamming. I am planning to make the paddles very flexible to reduce jamming. I don't want to add vibration motors.

    What designs/tricks/tactics are used in the industry to prevent jamming? I imagine this is a common problem. I'm not married to the paddle wheel idea, just to the motor I am using.

    Here's a picture of what I imagine miught happen.

    Much appreciation for any help!
  2. jcsd
  3. Dec 13, 2013 #2


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    You have an undershot drive wheel that pinches the material against the shelf. Consider an overshot wheel where the hopper material is placed on top of the wheel with a knife edge to cut the depth of material. The shelf is eliminated since the food will fall off the wheel into the tank.
  4. Dec 14, 2013 #3
    Adding on to what Baluncore said: look into airlocks or rotary valves.

    http://www.iac-intl.com/resource/airlock%20article%20for%20publish.pdf [Broken]
    Last edited by a moderator: May 6, 2017
  5. Dec 16, 2013 #4
    Thank you all for the valueable info. What do you think of this new design given the design suggestions?
    I did not understand what a knife edge is though in reference to wheels.

  6. Dec 16, 2013 #5
    DScheuf, don't feel insulted because I didn't name it after you. You get the next revision lol.
  7. Dec 16, 2013 #6
    Don't worry; it's not like I'll be bitter or anything. haha.

    I think the design looks good. I like how the vane will shear through the granular material.

    What kind of flow rates are you looking at?
  8. Dec 16, 2013 #7
    The motor is a clock movement. So 1 rotation every 12 hours. Or 1 rotation per hour depending on which "hand" i use.
  9. Dec 16, 2013 #8
    The motor is very weak, I doubt the vane could actually shear through a pellet.

    I didn't answer your question well. My fish usually eats 2 times per day, 5 pellets each time. So my design goal is to match that at a rate of 5 pellets every 12 hours.

    I chose the hopper design because it has the potential to hold a weeks' worth of food. Also because I could make wheels with deeper teeth to feed more fish should I buy more.
  10. Dec 16, 2013 #9
    Just a thought, but you could form the contact surface (between the vanes and the hopper) with a sort of foam material (that won't retain much moisture) or rubber skirt (think: the flipper/slapper thing on wheel of fortune) so that the binding force would be less. It's not catastrophic if your fish get 4 or 6 pellets rather than 5, so a little slip up here and there wouldn't kill you.
  11. Dec 16, 2013 #10


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    See attached. My knife edge solution.

    Attached Files:

  12. Dec 17, 2013 #11
    Baluncore, now I get it. I'm going to have a few designs printed up and see how they work. It will take me awhile to make each design in sketchup.

    Travis_King, that's a good idea.

    I'm going to post the results when I have something. Thanks for the help so far!
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