Simple Engineering Question

[MartyMcFly3]

First let me say this is not homework. I am trying to lift a PVC Cube box with some sort of pulley system using a tree branch acting as a drum but am having difficulty.

The PVC cube looks sort of like this only taller and a tiny bit wider:

What would be the best way to rig it so I can lift up all sides evenly? Any help is appreciated. Yes, I know this is a rather simple problem but I am having a moment (one of many ) of stupidity.

 

[olds]

A sling across the top?

 

[MartyMcFly3]

Right now I have 4 pieces of rope connected in the center of the top of the PVC cube. Wrapping around a piece of rope around the knot in the center doesn't seem to lift it up very easily or evenly. Trying to see if there's an easier way than that.

 

[Eli]

Engineering is a lot of "Whatever works.".

I don't see why your current method wouldn't work just fine. Tie the rope around your knot in the center, throw the rope over a tree branch, give it a tug and you would have the cube sky high in no time flat?

What exactly is the goal? To have the most elegant lift, or what?

 

[MartyMcFly3]

Engineering is a lot of "Whatever works.".

I don't see why your current method wouldn't work just fine. Tie the rope around your knot in the center, throw the rope over a tree branch, give it a tug and you would have the cube sky high in no time flat?

What exactly is the goal? To have the most elegant lift, or what?

I am going to be inside the cube (not lifted with the cube), and theres a chance it might drop. Don't want it to drop on me for one. So the goal is to have a close to perfect lift up off the ground so it doesn't hit me on the way up or if it drops.

 

[MotF Bane]

How will you be in the cube? Clinging to the pipes, or are you placing a flat floor on the bottom of it? Are the joints of the pipes going to support your weight plus their own weight plus a possible floor?

Beyond that, I'd tie four equal length pieces of rope to the upper corners, and tie them to each other above the cube, then hook the lifting rope to that.

 

[Eli]

I am going to be inside the cube (not lifted with the cube), and theres a chance it might drop. Don't want it to drop on me for one. So the goal is to have a close to perfect lift up off the ground so it doesn't hit me on the way up or if it drops.

Ahh.. I see.. I think. Hmm.

Well, to have the most even lift.. you need to pull equally on all sides.

Is there maybe some kind of "lift knot" that pulls directly from the center? I don't really know. I'm not a rope/knot expert.. lol

Making sure the four ropes tied to the corners are exactly the same length will go a long way towards making things lift evenly.

 

[MartyMcFly3]

How will you be in the cube? Clinging to the pipes, or are you placing a flat floor on the bottom of it? Are the joints of the pipes going to support your weight plus their own weight plus a possible floor?

Beyond that, I'd tie four equal length pieces of rope to the upper corners, and tie them to each other above the cube, then hook the lifting rope to that.

The cube looks like whats in the picture. There is no base. Its open on all sides. I'm just going to be inside it, but will not be a part of the weight of the cube in any way whatsoever. Was just explaining why I need a relatively straight up and down lift.

Your recommendation sounds like the current setup, and I worry it's not going to lift straight up and down. I tested it a little last night and it didn't seem to be a clean enough lift. Granted there's a big difference between a rafter in the basement as the drum and a 9' tree branch but....

 

[Eli]

What if you took the four corner ropes, and put the lifting rope in the center of them(the cross section of this would look kinda like the "five" side of a dice; four corners and one in the center), tie a knot at the bottom of the lifting rope for good measure, then use a few hose clamps to tighten the whole thing up? That would probably work pretty well for lifting from the center. Again, the trick would be to make sure your corner ropes are the same length.

Edit: I think this works better in my head than it would in the real world, unless you were using different size ropes, or something. Otherwise, it is going to be hard to make the four corners stay in that position with just hose clamps.

I am assuming this setup doesn't have to lift more than like, 20lbs? I don't think you have to worry about your ropes breaking, unless your "ropes" are fishing line. Just make sure your knots are secure.

It sounds like your main concern is lifting it cleanly up over you so it doesn't hit you when it lifts?

 

[spidey07]

4 points of contact on the corners with equal lengths rope to a single rope. Or two equal lengths of rope to opposing 4 corners. Wither way will achieve most strength/evenness.

 

[MartyMcFly3]

What if you took the four corner ropes, and put the lifting rope in the center of them(the cross section of this would look kinda like the "five" side of a dice; four corners and one in the center), tie a knot at the bottom of the lifting rope for good measure, then use a few hose clamps to tighten the whole thing up? That would probably work pretty well for lifting from the center. Again, the trick would be to make sure your corner ropes are the same length.

Hmmm.... The hose clamp thing is definitely a possibility, if anything for stability sake. I'm not really a knot guy either (know a few basics) so what I got is a clusterfuck of knots that meet in the center of this thing.

 

[spidey07]

Hmmm.... The hose clamp thing is definitely a possibility, if anything for stability sake. I'm not really a knot guy either (know a few basics) so what I got is a clusterfuck of knots that meet in the center of this thing.

The two equal ropes to all 4 opposing corners gives you no knots for these ropes. Then you could use a simple slip knot over the centers of both these ropes for the one lifting. Easy-peasy.

 

[MotF Bane]

The cube looks like whats in the picture. There is no base. Its open on all sides. I'm just going to be inside it, but will not be a part of the weight of the cube in any way whatsoever. Was just explaining why I need a relatively straight up and down lift.

Your recommendation sounds like the current setup, and I worry it's not going to lift straight up and down. I tested it a little last night and it didn't seem to be a clean enough lift. Granted there's a big difference between a rafter in the basement as the drum and a 9' tree branch but....

If you are inside it, how are you not going to be part of its weight?

Are you allowed to have multiple forces on it? You could add a rope to a lower corner, and have someone on the ground applying light tension to it for stability.

Is the tree branch smooth enough for a rope to pull over it? I would think the rafter would be a better drum than a branch, it'd be smoother.

 

[herm0016]

this is lolrigging....

i was the head rigger in a theater, flying stuff over people. I am also a certified crane operator.

what supplies do you have?
If all you have it rope i would use 2 equal length sections. tie them off to the cube, one length to each opposing sides.
If you have no hook on your lifting rope then tie a fairly tight loop, possibly using a double half hitch so that you can adjust the center of each of your supporting ropes. now lift the cube and adjust the support ropes so that they are even and lift the cube level and then cinch the half hitch knot.
Use a clove hitch and finish it with a half hitch to tie to the cube.

Realize that only 3 of the ropes will take weight and the 4th will be there for stability depending on your CG.

we used burlap bags over sharp corners for protecting the ropes, you could use this to protect the tree and rope.

clove hitch: http://www.animatedknots.com/clove/...ge=LogoGrog.jpg&Website=www.animatedknots.com

use this or a clove and a half hitch for the cube: http://www.animatedknots.com/roundt...ge=LogoGrog.jpg&Website=www.animatedknots.com

 

[Eli]

If you are inside it, how are you not going to be part of its weight?

Are you allowed to have multiple forces on it? You could add a rope to a lower corner, and have someone on the ground applying light tension to it for stability.

Is the tree branch smooth enough for a rope to pull over it? I would think the rafter would be a better drum than a branch, it'd be smoother.

It's just a PVC cube-skeleton. No walls.

Like I said, whatever works. Your current knot setup probably has the potential to work well, but it will need tweaking to get all the forces right for a clean lift.

 

[MartyMcFly3]

It's just a PVC cube-skeleton. No walls.

Like I said, whatever works. Your current knot setup probably has the potential to work well, but it will need tweaking to get all the forces right for a clean lift.

After some more tweaking, it did. I had a feeling I was on the right track, just couldnt figure out what was wrong. I just cleaned up the current setup and made some quick switches based on the advice in this thread.

I have 4 pieces of rope knotted around the corners. Sadly after making a much better/stronger knot than before, they were too short to tie in the center. I then tied 2 pieces into a knot together and the 2 other pieces into a knot together. I then tied the pieces together using more rope and was able to use the same piece of rope for the pulley. Using the rafter, it seems to lift a lot smoother than before and is probably my best shot at getting it even.

It's not perfect, but whatever works. Thanks guys.

 

[DrPizza]

Okay, someone needs to ask...

wtf are you doing hanging from a tree in the middle of a pvc cube? I hope there isn't some bizarre sort of autoerotic thing going on here.

 

[boomerang]

Halloween prank would be my guess.

 

[Nik]

 

[crashtestdummy]

Okay, someone needs to ask...

wtf are you doing hanging from a tree in the middle of a pvc cube? I hope there isn't some bizarre sort of autoerotic thing going on here.

Free Chicken?

(Obscure Aressted Development reference)

 

[MartyMcFly3]

Nik, closer to the 2nd, only there's a knot in the middle where it's getting pulled up from. My original idea was the first image. Like I said, it's not the best design I'm sure, but it works for what I'm trying to accomplish with it.

Not a halloween prank. Not "hanging" from a cube. The cube will have a cloth around it, and I will be underneath. When someone lifts it, it will "reveal" me.

 

[iGas]

Tie rope to 1 corner then loop one end through the next corner,
Then rope up to branch,
then rope down to center of rope loop,
then up to tree branch,
then down to 1 free corner,
rope through the center of loop,
then back to the last free corner.

 

[iGas]

Start rope at the green arrow follow the red arrow then blue arrow from center.

Is this what you wanted?
No knot in the middle?

 

[MartyMcFly3]

Start rope at the green arrow follow the red arrow then blue arrow from center.

Is this what you wanted?
No knot in the middle?

If you make the two ropes going up in your picture smaller, and connect the two with a piece of rope in the middle, then lift by the middle rope, thats what I have. It does seem to work which makes me happy.

 

[Matthiasa]

Fun fact(that may have alreayd been listed): If it falls due to something breaking there is little chance of it not turning somewhat.