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-   -   How to elevate object evenly (http://www.physicsforums.com/showthread.php?t=579611)

 jugnut Feb20-12 06:12 PM

How to elevate object evenly

2 Attachment(s)
Hello,

I am trying to create a mechanism that will elevate an object evenly. I have built (this is a real life case) a "cage" which is 2m x 1.5m by 1.5m tall and in the cage there will be placed an object with a geometry similar to the one in the drawing attached.

I have thought of rising the object by placing two ropes under it and bringing the ropes over the side of the cage and pulling from there. However because of the geometry of the object when you pull the same amount from both ropes, the object doesn't rise evenly.

So far I have obtained an equation that relates the relation between what the blue rope rises and what the red rope rises as a funtion of the height the object has risen (this relation changes with the height). I don't know how to obtain it formally, so what I did is draw the object (in Autocad) at 0.25 intervals, then I drew a 0.5m pull from each rope, obtained the relation between what each rope rises at each interval, and then solved a system of equations. My results were:0.589x^3+2.711x^2+4.526x+3.974 with the origin set at the top right end of the cage and "y" positive upwards.

However I have no idea of mechanical engineering nor how to design a mechanism that will elevate the object evenly. I'm thinking that maybe will pulleys, but I really don't know... Please help.

Thanks!

 OldEngr63 Feb20-12 07:41 PM

Re: How to elevate object evenly

Can you get under the object an lift it with either (1) a group of hydraulic cylinders, or (2) a group of screws, geared to rotated in unison so that they lift together? Can you get above the object and simply lift it in a sling over the center of mass?

There seem to be a lot of possibilities, depending upon the work space available to be used.

 jugnut Feb21-12 02:46 AM

Re: How to elevate object evenly

1 Attachment(s)
Quote:
 Quote by OldEngr63 (Post 3774707) Can you get under the object an lift it with either (1) a group of hydraulic cylinders, or (2) a group of screws, geared to rotated in unison so that they lift together? Can you get above the object and simply lift it in a sling over the center of mass? There seem to be a lot of possibilities, depending upon the work space available to be used.
Well, as I have said this is a real life case. It's actually a model I'm building, and it's quite huge. Plus, it has to be easy to be put together, transportable and my budget is really limited.

I have attached a image of what I have so far. Maybe the photos don't give a sense of scale, but it's quite big. The tower (the image on the right) would go on top of the cage (the platform of which it would rest hasn't been built yet). Thanks

 OldEngr63 Feb21-12 10:28 AM

Re: How to elevate object evenly

You did not answer any of the questions that I asked, so I have to say, all of my questions are still on the table.

 jugnut Feb21-12 01:11 PM

Re: How to elevate object evenly

1 Attachment(s)
Quote:
 Quote by OldEngr63 (Post 3775704) You did not answer any of the questions that I asked, so I have to say, all of my questions are still on the table.
Of the options you gave, the most I could do is get a ladder beside it. The other options are too expensive.

To clarify things, attached is a graph which shows the relation between what the blue rope rises and what the red rope rises, as a function of the height the object has risen. The origin is at the upper right side of the cage. Note that when the object is at -0.4m, you have to pull 3 times more from the red rope than from the blue one.

 OldEngr63 Feb21-12 02:46 PM

Re: How to elevate object evenly

But you still have not addressed the question of what space is available to develop a solution. Can you get room to work under the frame? Can you get room to work over the frame?

There are all sorts of lifting mechanims that might be considered, but each of them requires some space, some power, etc. What is available to work with here?

 Mech_Engineer Feb21-12 05:11 PM

Re: How to elevate object evenly

You haven't been very specific in your application, so it's hard to know what migh work for you. Right now it seems as if you're manually pulling the ropes from the side of the enclosure. A better way to go would be to support the "object" in a track which supports it, and then have a single rope which is used to raise or lower it.

The other solution would of course be to have the two ropes be symmetrically opposite from one another so they have the same trig relations.

 jugnut Feb21-12 05:15 PM

Re: How to elevate object evenly

Quote:
 Quote by OldEngr63 (Post 3776237) But you still have not addressed the question of what space is available to develop a solution. Can you get room to work under the frame? Can you get room to work over the frame? There are all sorts of lifting mechanims that might be considered, but each of them requires some space, some power, etc. What is available to work with here?
Ok some context: I'm an architecture student, and the model is part of an assignment which we have to hand in at the end of May. We are working as a group of three people.

So, because we are students and it's our money we are investing in the model, we aim to spend as little as possible.

At the moment, we are working in a basement, but the model has to be showcased once a month in class. Hence, the model has to be dismountable and transportable.

And we have no means of our own, or means which can be lent to us to lift the tower at the moment (hydraulic cylinders, screws, cranes, forklift...). The most we could manage is ladders, ropes, our hands...

Oh and the tower is extremely fragile. It consists of wood columns and styrodur slabs which aren't fixed to the columns, they just sit on them.

 OldEngr63 Feb21-12 06:10 PM

Re: How to elevate object evenly

Can you place the irregular base of your tower on a flat, rectangular base plate? Then you could simply use ropes attached to the corners of the rectangular base plate and suddenly the geometry is simple again.

 jugnut Feb22-12 05:06 AM

Re: How to elevate object evenly

Quote:
 Quote by OldEngr63 (Post 3776630) Can you place the irregular base of your tower on a flat, rectangular base plate? Then you could simply use ropes attached to the corners of the rectangular base plate and suddenly the geometry is simple again.
Well, in reality there is going to be a big void at the top of the cage and the cage is only going to be covered at the part where the tower rest. However it could be a compromise solution, lifting it with a symmetrical board, and then sliding it to its definitive stand. In the end it may be simpler than figuring out how a pulley mechanism would work in an asymmetrical rig.

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