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What is the important dimension in this brain teasing system?

  1. May 15, 2013 #1
    Though it may seem like it, this certainly isn't a homework question so I hope I don't offend anyone with it's placement. This is a simple drawing of a hydraulic mechanism that me and a friend are building. There is much debate about where we need to improve so we are leaving it up to you, the 'professionals' to settle the argument.

    I included all the details in the attached drawing. Let me know what you guys think.

    View attachment PHYSICS POST, simple.pdf
    For clarification, points A, B, C and D are all PIVOT POINTS!!!
    Last edited: May 15, 2013
  2. jcsd
  3. May 15, 2013 #2


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    Upon what do you and your friend disagree?
  4. May 15, 2013 #3
    Which items (linkages BD or CD, pivot points B, D, C or A, Moment Arm 1, 2 or 3) need to be adjusted to create the most lift possible at point C with the least amount of force at F? Perhaps the simple/general question is, 'What can we do in this system to maximize vertical lift at C with minimal F and without changing the angle of vector DF.
  5. May 15, 2013 #4
    Its still confusing to me. Why not just use a block and tackle/compound pulley? Why are you using hydraulics and what is it for?
  6. May 15, 2013 #5
    Because once it is folded in it must push out as well. The movement out is not an issue though. Attached is the detailed drawing of the system. Luckily my day job is in SolidWorks. HA HA.

    Attached Files:

  7. May 15, 2013 #6


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    You might want to review how a lever works as a force or displacement multiplier. If you want more force at the load end you sacrifice displacement, and vice verse ( more displacement at the load end means less force at the load end ).

    A simple lever, or a modified L shaped lever ( to change direction of the force and displacement ) have shear in the members. The way your linkages are set up it appears the members 1,2,3 will be in tension or compression, with minimized shear.

    What you will have to do is
    as BD rotates around fulcrum B, point D moves along an arc of a circle. Member DC comes along for the ride lifting your load M. If CA was not there ( ie CD would hang vertical ) then the displacement of load M would be merely a simple angle function of movement of BD. Since CA does control some of the movement of load M, at least horizontal and vertical you will need to find the more complicated equation that relates the angle of movement of BD to that of the load M using basic trigonometry.

    That is the way I see the solution to your problem.
    and you can lengthen or shorten the members and see what that gives you as a result to maxmize displacement, if that is what you are after when you say lift.
  8. May 16, 2013 #7


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    Your first diagram shows mass M and link CD attached to the same point on link AC. However having looked at your second diagram I suspect it would be better to show mass M attached to a different point.
  9. May 16, 2013 #8
    256 & CWatters

    I appreciate both of your input. It would probably help if I told you that the mass M is really a frame member that extends out horizontally. Once it starts to lift/rotate up around hinge A it will immediately be moving easier and easier. Because of this, I am only concerned with maximizing "lift" at the moment that it is just starting to move.

    It seams to me that getting Moment Arm 3 (sorry if my terms are inaccurate) as long as possible would give me the most lift possible. Also, getting angle BDF to be as close to 90 as possible.
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