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Table Jumper

  1. Oct 31, 2006 #1
    I need ti build an apparatus that will move from one table top to a second table top over a two foot gap.

    The apparatus can have no stored eergy other than gravitational potential energy. Springs or other items that depend on a spring-like mechanism to provide thrust will not be permitted. No batteries or motors allowed. No compressed air or gas cylinders are permitted. Your apparatus should employ materials that cost no more then 10 dollars. The height shall not exceed 60 inches and the base shall not exceed 17" x 17"/ The weight must be no more then 5lbs and not less then 1lbs.

    I am lost and have no idea what to do:confused:
     
  2. jcsd
  3. Oct 31, 2006 #2

    berkeman

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    Can the starting position be hanging over the edge of the starting table? And the ending position hanging over the edge of the ending table (but no longer touching the starting table)? If so, there's a pretty easy way to do it.
     
  4. Oct 31, 2006 #3
    I left some important details out.

    The "Jumper" must begin on a table, in a self-supporting and stable condition and unattached to anything. The "jumping" process must be initiated by using scissors to cuta string internal to the apparatus. Everything on the first table must be transfer to the second table. The apparatus may hangover the edge of the second table, but all if it must be at least 2 feet away from the first table. Nothing can be left behind on the first table. Maximum time to move from the first table to the second table is one minute. No ramps are allow.
     
  5. Oct 31, 2006 #4

    berkeman

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    But if the whole apparatus must be at least 2 feet away from the first table, how can it overhang at all in the 2 foot gap?

    I think my idea would still work without a beginning and ending overhang, but it works a lot easier if the apparatus only has to move a few inches and be stable in the starting and ending position....
     
  6. Oct 31, 2006 #5
    Let me hear your idea.
     
  7. Oct 31, 2006 #6

    berkeman

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    "Oh sure, I tell you, you tell the next guy, and pretty soon we're in another ice age!" (quiz question -- what movie is that from, and why is it applicable?)

    Well let's take the case where the device could overhang at start and finish, as long as it is stable and not touching the other table. The goal is to have it move on treads and transfer its horizontal center of mass as it moves, so that it's HCoM is way back at the start (stable on the first table), and way forward at the end (stable on the second table). One way to do this is to use a weight going down a low-friction ramp that angles from back to front, and use the weight going down the ramp to also drive the treads via a string a pulley system. So when you start the creeper, it creeps forward a few inches, still with its HCoM far enough back to be stable on table 1, and then as the treads span the gap and the creeper treads start creeping onto table 2, the HCoM transfers forward down the ramp, and by the end of the travel down the ramp, the HCoM is over the 2nd table and the treads have left table 1 by some amount. In this scenario the creeper only moves forward a few inches (call it 6-8 inches), and the weight transfers from way at the back end (and at the top of the ramp) to way at the front end (and at the bottom of the ramp).

    Now, you can do some sketches based on that starting idea and the dimensions that you've been given for allowed apparatus, and see if you can come up with a combination that will move the full distance. If a simple ramp wouldn't do it, you could add in some pendulum mechanism that transfers the HCoM forward during the part of the crawl where the tread is in contact with both tables. Interesting project....
     
    Last edited: Oct 31, 2006
  8. Oct 31, 2006 #7

    berkeman

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    Another mental thought experiment would be to picture a square structure a little over 2 feet in size. When you start it off, it rolls toward the 2nd table and spans the opening, and then rolls one more time to transfer to the 2nd table. What system of pendulums and weights can you think of to make that 2-step motion happen?
     
  9. Oct 31, 2006 #8
    A system of pullies?

    Wouldnt this require a lift of some type to transfer over?
     
  10. Oct 31, 2006 #9

    berkeman

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    No, the way I have it sketched with one square box and two pendulums looks like it has a shot at it. It might require a little creativity with the way the first pendulum is stopped, though.

    Think a little about what it would take to make a square box roll twice (two sides) to go across the gap between the tables. Like, you can do it by pushing at the correct top corner for each of the two roll-overs, right? Now think about how you might be able to position two pendulums to give you something like those corner forces....:biggrin:
     
  11. Nov 1, 2006 #10

    FredGarvin

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    Real Genius. Applicability? None that I can tell.
     
  12. Nov 1, 2006 #11

    berkeman

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