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Physics equation for the stable height of the pole?

  1. Mar 5, 2015 #1
    Hi Guys,

    I am new to this forum and interested in physics/Maths. Need your help with one of the problem I am trying to solve.

    The problem:
    Someone needs to build a 51 feet tall pole (usual shape of long lamp posts, thick at the bottom and thin at the top). but they want to make this pole such that it can be brought down and up with least effort, for which they are using a gear box with the handle, a strong wire will be attached to the bottom of the pole which will go into the gear box and on rotating the handle the wire will windup in the gearbox and allow the poles head to be brought down or stand it back up. I hope this makes sense.

    For this a base will be made inside which channels wills be fit and within those channels the pole will go up and down. ( Please see attached pic)

    Could you please let me know the physics equation that calculates the stability of the pole with inputs of:

    1)Channels length inside the base or height of the base
    2)channels length outside the base
    3)length of the pole
    4)weight of the pole
    5)weight of the channels(optional)
    6)distance of gearbox from the channels/pole

    Please let me know if you need further info about this. please check the attached image.

    This will be a very interesting pole equation and very helpful. Many Thanks in advance.
    Nishaan.JPG
     
  2. jcsd
  3. Mar 5, 2015 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    That's a pretty tall pole to not be using guy wires. Can you use guy wires for stability and to erect and lower the pole instead?
     
  4. Mar 5, 2015 #3

    sophiecentaur

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    Gold Member

    What you are describing is termed a 'Tabernacle' when used on sailing boats. You may find it useful to google that term and you will find a lot of qualitative (at least) discussions abut the problem. If you are really wanting to raise a 51 ft mast of any significant mass then you will need a pretty hefty installation and a tall tabernacle. Using sheerlegs, which are mounted at right angles to the mast, can reduce the loading during raising or dropping masts (google can help here too). You will definitely need some extra spar for this exercise (or a large diameter wheel).
    To do the sort of calculation you are after, requires the application of the principle of moments and is fairly straightforward. Frankly, I should say that you would need the help of a mechanical Engineer if you actually plan to do this for real. It is a potentially hazardous thing to do and you need everything to be strong enough - with lots to spare. And there could be the small matter of liability and insurance, although I raise and lower my 10m mast every year, relying on back of a fag packet sums when I designed the tackle. I use the s/s rigging that's on the mast already and it is a bit of a scary exercise for the first few times. Then there are windy days . . . . . . .:woot:
     
    Last edited: Mar 5, 2015
  5. Mar 6, 2015 #4
    Thanks very much for replying.... This video might give you some more idea what I am trying to achieve. although the pole in the video is brought down and up using the hydraulic lift system.

    I want to create the same using the grearbox and hand operated rotating handle.

    In case you can point me to the right source of information, it will be great.

    Many Thanks..

     
  6. Mar 6, 2015 #5

    sophiecentaur

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    Gold Member

    Seeing all those people in your video further convinces me that you need professional help with this. You could have a disaster on your hands. You could, perhaps, copy the arrangement in the video but replace the hydraulics with a lever system. But this is not a suitable project for a first timer who, as you tell us, doesn't know basic Mechanics. Everything about the mechanism needs to be specified - down to the arrangement and sizes of nuts and bolts used, the gauge of the material for the tabernacle and the diameter of the pivot.
    Don't be misled by the jolly decorations on the mast in that video. it needs to be done properly; you owe it to the spectators.
    i think that help from PF could be against our practices and I will check with the Mods.
     
  7. Mar 6, 2015 #6

    berkeman

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    Staff: Mentor

    Agreed. Thread is closed.
     
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