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Designing a most powerful/efficient vacuum

  1. Aug 15, 2007 #1
    I'm wondering what is required in terms of design and materials in order to produce a vacuum that is powerful and efficient. I need a vacuum powerful enough to hold a 30 pound weight on a vertical wall (and move around on the wall with wheels)
     
  2. jcsd
  3. Aug 15, 2007 #2
    How do you intend to create the vacuum around the wheels?
     
  4. Aug 15, 2007 #3

    mgb_phys

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    You can never get more than 1 atmosphere of pressure from a vacuum. As you get a closer to a perfect vacuum you only approach this figure and of course it becomes exponentially harder and harder to reach. To just get some force you only need to get a 99% vacuum.

    The TOTAL amount of force will depend on the surface area under the vacuum, a 1cm^2 path will give you about 1Kg, a 1m^2 will hold 10 tons.
    What is probably going to be tricky is to seal the edges of the vacuum in such a way that they can still move while not allowing any air in.
     
  5. Aug 15, 2007 #4

    Danger

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    Sounds like an 'inverted' hovercraft to me.
     
  6. Aug 15, 2007 #5

    mgb_phys

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    Exactly, but a real hovercraft is much easier to seal the skirts.
    The weight of the craft gives you a good seal and you turn up the power to break it, an inverted hovercraft you have no seal wthout power - a bit less stable to get started.
     
  7. Aug 15, 2007 #6

    Danger

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    Yeah, I didn't think of that. I wonder if some elastomer similar to 'Slime' might be an appropriate material. It would be difficult to move over a surface, but it sure as hell should provide a seal.
     
  8. Aug 16, 2007 #7
    Well does it really have to seal completely to provide suction? I'm thinking just a partial seal with a little bit of the air escaping will still allow the movement and the ability to stay on the wall.
     
  9. Aug 16, 2007 #8
    Is the wall flat? If it was the texture of sealed and painted concrete block and has a 1/4" deep grout joints every 8" to 16" then your job just got a little more complex.

    Maybe your skirt can be a kids pool noodle float toy. That should compress some, and perhaps coat it with something slick (not sticky).

    I would consider caterpillar track drive over wheels. How about many many small wheels or castors?
     
  10. Aug 16, 2007 #9
  11. Aug 16, 2007 #10

    russ_watters

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    The calculations are exactly the same as for a hovercraft. You have a fan with a certain static pressure and airflow and a skirt some distance from a wall (thus giving you an area and a velocity of airflow). Static pressure times skirt area equals suction force. Pick a fan and see what airflow you get with what suction force and from that, calculate how far the skirt can be from the wall.

    There are many threads about hovercraft and online calculators. They'll work fine here.

    Oh, one thing, though: the force you are looking for is not the weight of the craft, but the normal force toward the wall. The wheel friction is what actually holds up the weight of the craft. So your attraction/normal force will need to be somewhere on the order of double the weight of the craft (with a .5 coefficient of friction).
     
    Last edited: Aug 16, 2007
  12. Aug 16, 2007 #11
    Man you guys know a lot. :) Even though I don't understand everything you said I'll take your advice and look for the hovercraft stuff.
     
  13. Aug 17, 2007 #12
    Based on the example pictures I guess only four wheels are not a problem if the frame is rigid enough. Kind of looks like the Mars rover.

    You are not trying to peek over the wall at a local nudist colony are you?:biggrin:
     
  14. Aug 17, 2007 #13

    DaveC426913

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    I'll bow to your guys' greater wisdom on the subject but I would have thought that the suction required would be too high to hold up any reasonably-sized object. I would would dismiss the video as hoaxed, as I can't see how that little thing could be so small and still hold itself to a brick wall.

    Also, how stealthy can it be if it's as loud as a Hoover?
     
  15. Aug 17, 2007 #14
    maybe it gets used with a little cover fire or after a few explosions have already taken place.

    Good question actually.
     
  16. Aug 17, 2007 #15

    russ_watters

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    I didn't make any claims about feasibility - Paulo will have to do the calculations I described, then find out if there are any reasonable-sized fans that meet the requirements.
     
  17. Aug 17, 2007 #16

    Danger

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    Yeah... that thing hurt my ears.
    The video looks real enough, but I'm also having a bit of a credibility problem. My special area of interest is the part where the front and rear sections sequentially detach from the wall in order to turn the corner. New we have one little bitty thing holding up twice as much weight as usual, and without even having the friction of the other wheels to lessen the torque around the support point. (In fairness, though, it does seem to rotate downward until it reattaches the second section.) This is not the first wall-crawling machine that I've seen, but it is the first one that can handle bricks. I'd like to find out more about it.
     
    Last edited: Aug 17, 2007
  18. Aug 17, 2007 #17

    russ_watters

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    We want you to learn for yourself (as opposed to doing your calculations for you), but give it a shot and then come back with more questions. We'll give you another push.
     
  19. Aug 17, 2007 #18
    I recently stumbled across an web-page and picture of a caterpillar walking machine hovercraft. The pad in a long line of other pads would inflate and then deflate causing the contraption to move forward in sequence.

    I suppose one could do the same thing with suction power.

    I'll post it when I find it, but it might be a while.
     
  20. Aug 17, 2007 #19
    Russ, I really appreciate that you want me to learn for myself. I am still a little bit confused though and wouldn't mind a point in the right direction. (like a link to one of the calculators) Cause I haven't been able to find them.

    Also does anyone know what kind of material is good for this type of work.

    EDIT: Also, I'm like 99% sure that video is real. It's developed by a big company and the technology is actually patented.
     
    Last edited: Aug 17, 2007
  21. Aug 18, 2007 #20
    Ok, I'm sorry for double posting but I have one more question. You said that the calculations required were the same as for a hovercraft, except a fan is a fan and will blow away no matter what. What do I use to create the suction? Just invert the fan blades or what.

    I found a calculator and it has given me confidence to actually try making this but I don't want to blow I want to suck.
     
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