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Finding the equation of a system involving dashpots and mass on wheels

  1. Jun 4, 2011 #1


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    1. The problem statement, all variables and given/known data
    consider the mechanical system below. Find the equation depicting the system. u is the input force. sorry for the poor picture, I had to draw it on my tablet...

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    2. Relevant equations

    3. The attempt at a solution
    I'm not sure how to treat the dashpot in parallel with the mass. I came up with the following system of equations:

  2. jcsd
  3. Jun 4, 2011 #2


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    hi lzh! :smile:

    according to http://en.wikipedia.org/wiki/Dashpot, the resistance is porportional to the speed :wink:
  4. Jun 4, 2011 #3


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    oops I mistyped...
  5. Jun 5, 2011 #4
    I can't tell you anything for sure since I haven't done these problems in years. The way I used to check out the mechanical "circuit" when I got overwhelmed was based on my electrical knowledge. Your dashpot is a resistor and your mass is an inductor. Always use this as a double check when you're unsure of a mechanical setup. The info for the electrical setup will always be more easy to find.

    EDIT: Looking at your equations of motion now though, I think you have it or are close. There is no need to fudge with the circuit. Just find X and Y based on input u.
    Last edited: Jun 5, 2011
  6. Jun 5, 2011 #5


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    after some more modification, but i'm still unsure...
  7. Jun 6, 2011 #6
    For starters:

    Note that u would be a velocity input, not a force input.

    b is by' - it has no contact with the velocity at x

    and I think for m it is m(y"-x")

    I haven't checked your eqautions yet, so patience please
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