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Winch loads and what is happening when you winch

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mrblaine

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If you give a good tug between points 2 and 3 toward point 1 do the values equal out at 1, 2, and 4? Just something I thought of to try and combat the friction losses (even though in the real world there will be friction losses)
Realistically, the worst friction loss I believe we will see is in the snatch block back to rig scenario. I'm using a very low friction snatch block and if you look at the loads on that set up, it is very low or enough to ignore.
 

FireJeep

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Although you see an increase on the COD pulley it is not what I was expecting, we have done similar experiments except with rope rescue gear and simple mechanical advantage systems (we do not use winches to pull people) and found the increase to be higher on the COD. This is very interesting, I wonder what is causing the difference? We may have to do our experiments again and see if we can replicate your findings. Thanks MrBlaine.
 
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mrblaine

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Although you see an increase on the COD pulley it is not what I was expecting, we have done similar experiments except with rope rescue gear and simple mechanical advantage systems (we do not use winches to pull people) and found the increase to be higher on the COD. This is very interesting, I wonder what is causing the difference? We may have to do our experiments again and see if we can replicate your findings. Thanks MrBlaine.
Thank you for the diagrams and info to get this going. To be clear, I don't just set it up and when I see the result I am after, stop there and call it good. I shake, change, move, rattle and re-rig if needed to get it to be as clear and repeatable as possible so I'm pretty confident this is a scale representation of real world numbers. (barring stupidity and unforeseen complicating factors)
 

FireJeep

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Thank you for the diagrams and info to get this going. To be clear, I don't just set it up and when I see the result I am after, stop there and call it good. I shake, change, move, rattle and re-rig if needed to get it to be as clear and repeatable as possible so I'm pretty confident this is a scale representation of real world numbers. (barring stupidity and unforeseen complicating factors)
You are more than welcome, glad to be of assistance. When we set up systems I have a couple of high end load cells that blue tooth and all kinds of fancy crap, I am wondering if our results are different because of load types. We use dead loads, there is no wheels on a 200# manikin hanging over a cliff face...... not sure why that would matter but we will do some trials and see if we can replicate what you have found.....
 
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mrblaine

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You are more than welcome, glad to be of assistance. When we set up systems I have a couple of high end load cells that blue tooth and all kinds of fancy crap, I am wondering if our results are different because of load types. We use dead loads, there is no wheels on a 200# manikin hanging over a cliff face...... not sure why that would matter but we will do some trials and see if we can replicate what you have found.....
I had a short break while a rig was out on a test drive so I went and played with it some more. Angle is critical to predict the loads we should see. I did not have a perfect 90 degree angle, closer 98 degrees so that accounts for some of the disparity.

Now I need a big angle finder to mess with so that a load can be shown at accurate angles. You also know which one I'm most interested in since very few understand just how high the loads get.
 
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pagrey

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Realistically, the worst friction loss I believe we will see is in the snatch block back to rig scenario. I'm using a very low friction snatch block and if you look at the loads on that set up, it is very low or enough to ignore.
Ignore friction, it's the only reason your numbers aren't what the math says it is supposed to be. That's the ONLY thing you are doing with this whole experiment is measuring friction. Part of doing good science is understanding what your results are telling you. The answer to the 90 pull is 410 lbs, try to look at your results and figure out why it isn't that number. You aren't going to redefine vector math with this experiment.
 
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jjvw

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I'm having a hard time understanding how a frictional loss through the pulley would translate into a reduction of pulling force predicted by the math. Where does that force go if it isn't being transferred to the various anchor points?
 
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mrblaine

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Ignore friction, it's the only reason your numbers aren't what the math says it is supposed to be. That's the ONLY thing you are doing with this whole experiment is measuring friction. Part of doing good science is understanding what your results are telling you. The answer to the 90 pull is 410 lbs, try to look at your results and figure out why it isn't that number. You aren't going to redefine vector math with this experiment.
I never dispute math. I dispute theory over practical application all the time. I am not disputing the math here, just trying to understand what I'm seeing and why I am seeing it and how we can all use that when we are rigging to keep us safer. Your post helps a bunch with that, so thank you for that.

The other thing I am trying to figure out is how the numbers should add up based on what the load is to move the rig.
 
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mrblaine

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I'm having a hard time understanding how a frictional loss through the pulley would translate into a reduction of pulling force predicted by the math. Where does that force go if it isn't being transferred to the various anchor points?
If you could watch the scales, it is interesting that I have to bump it up over a 300 lb target load by 40-50 lbs so it will settle back at my number. Not fully sure what is going on there other than some line creep and dynamic versus static loading.
 
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jjvw

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It shouldn't make a difference once all the stretch is taken up, but would a steel cable show the same results?
 
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mrblaine

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It shouldn't make a difference, but would a steel cable show the same results?
In order for me to know that, I would have to know it is coming from the synthetic. I don't know that, I only suspect it. I am dealing with a lot of moving parts though and all of them need to set into shape under load which for some are very small loads. I am astounded at the number of connections I keep making and why I am happy I have so many soft shackles, steel shackles, odd bits of winch line, and such.
 
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fuse

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It shouldn't make a difference once all the stretch is taken up, but would a steel cable show the same results?
If you had two set ups, one with steel and one with synthetic, with the same geometry and the same loads at the anchor points, why would the stretch matter?
 

jjvw

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If you had two set ups, one with steel and one with synthetic, with the same geometry and the same loads at the anchor points, why would the stretch matter?
It shouldn't. It's just a variable that I'm possibly not understanding the effects of.
 

Sundowner

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It shouldn't. It's just a variable that I'm possibly not understanding the effects of.
At least you've moved to "possibly." I'm still stuck on "dafuq is this numeric witchcraft?" and I'm looking for my old textbooks.
 

pagrey

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If you could watch the scales, it is interesting that I have to bump it up over a 300 lb target load by 40-50 lbs so it will settle back at my number. Not fully sure what is going on there other than some line creep and dynamic versus static loading.
You might look at static vs dynamic friction, static is much higher. That's why things tend to stick still and then when they start moving they move allot.

I almost feel bad for even mentioning it but you are also pulling on the polaris tires at an angle and they will act like soft springs side-to-side but stiff springs front-to-back because of the tire construction. At the loads you are pulling it might make a difference if the polaris is inline with #3 so the tires are loaded straight on. When it's loaded they way you had it setup push the polaris side-to-side and watch the scales especially #4, then push it front to back with the same force and pay close attention to #2 and you might see what I mean.

Fun project.
 
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mrblaine

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You might look at static vs dynamic friction, static is much higher. That's why things tend to stick still and then when they start moving they move allot.

I almost feel bad for even mentioning it but you are also pulling on the polaris tires at an angle and they will act like soft springs side-to-side but stiff springs front-to-back because of the tire construction. At the loads you are pulling it might make a difference if the polaris is inline with #3 so the tires are loaded straight on. When it's loaded they way you had it setup push the polaris side-to-side and watch the scales especially #4, then push it front to back with the same force and pay close attention to #2 and you might see what I mean.

Fun project.
I'm aware of the Polaris tires. It does the same thing regardless of angle of pull against them. The phenomenon has been present no matter what I've used for anchors or how I have rigged it. It has done it when I did my first test to see how the cart worked. Pole as one anchor, straight to cart, straight to other anchor to see how the scales would work in a straight line pull and if those numbers would balance out. Near as I can tell, as long as they settle and stop moving (they do very quickly) that is all that matters.
 

FireJeep

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What is the rolling resistance of your "load", are the wheels moving freely? I am trying to wrap my head around the scale on the back, is there additional weight back there? Is that simply measuring the force applied?
 

FireJeep

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This is a great experiment, much to be learned here. Thanks for taking the time and effort!
 
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mrblaine

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What is the rolling resistance of your "load", are the wheels moving freely? I am trying to wrap my head around the scale on the back, is there additional weight back there? Is that simply measuring the force applied?
As I said previous, it was easier to put the winch load scale at the back of the cart inline with the anchor rather than build a sliding tray to mount the winch on. The rolling resistance is very low. Those are high dollar casters and the force to move it on the smooth concrete is sub 5 lbs if I had to guess. I can check it, but it is very low.