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Winch loads and what is happening when you winch

FireJeep

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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.
Ok, maybe I am being a little dense here, when conducting the experiments the cart does not actually move, the winch just applies a load as measured by the scale on the back of the cart? I am curious if there are differences in forces based on where the load is in relation to the winch? Would this method be more of a static load than vs. a dynamic load? Would that even make a difference on the measures you are recording? curious to see what you do next with this.....
 
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mrblaine

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Ok, maybe I am being a little dense here, when conducting the experiments the cart does not actually move, the winch just applies a load as measured by the scale on the back of the cart? I am curious if there are differences in forces based on where the load is in relation to the winch? Would this method be more of a static load than vs. a dynamic load? Would that even make a difference on the measures you are recording? curious to see what you do next with this.....
The cart essentially does not move. The rear scale is just showing the force exerted by the winch to move your rig. It would show the same load if the winch were on a sliding tray and the scale between the tray and chassis.
 
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Goatman

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I just noticed the "front" tires are at a 90* to the pull direction. And while this would help explain some of the oddities in the scale numbers, I was still way off. This is why you don't put a 4,000 lb winch on your Jeep
Unfortunately when I went to school we had just invented the abacus. Being able to use fingers on both hands to count was still cutting edge.😉
 
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mrblaine

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I just noticed the "front" tires are at a 90* to the pull direction. And while this would help explain some of the oddities in the scale numbers, I was still way off. This is why you don't put a 4,000 lb winch on your Jeep
Unfortunately when I went to school we had just invented the abacus. Being able to use fingers on both hands to count was still cutting edge.😉
The front casters turn very easily. They are 90 to the pull because I shake the cart around to make sure there is nothing affecting the loads. Ya'll are gonna make go put a scale on it to see what the break away torque is, ain'tcha?
 
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mrblaine

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We gotta know the bearing preload on those swivel casters!
My patience grows thin when this shit devolves into the mind numbing minutia of inconsequential details that distract from the important aspects of the concepts. Or put another two ways, why I don't do build threads and I'm a hare's breadth from deleting the whole mess.
 

jjvw

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What would happen to the force readings if the winch/cart was placed between the Polaris and the pulley? In the physical world, does the location of the pull effect how the load is distributed throughout the system after normalizing the system via shaking? Would moving the winch behind the pulley make the demonstration more closely match the math?
 
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jjvw

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I just noticed the "front" tires are at a 90* to the pull direction. And while this would help explain some of the oddities in the scale numbers, I was still way off.
...
The shaking of the loaded system is intended to remove binding, sticking and settle undistributed loads from things like the casters and extra slack in the line/connections.

A familiar situation for many here is using an engine hoist. The hoist is on casters. As the engine is lifted, the hoist will move and shift as the force of the engine load attempts to normalize. Giving the hoist an occasional small shake during the lift will help further equalize the load and prevent unexpected shifts and jumps.

The point being that the resistance and binding from the cart ought to be inconsequential for the purposes here. And moreso after the cart and other components in the system have been normalized after a good shake.
 
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Sundowner

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I think I've finally wrapped my head around the change-of-direction thing...so that's helpful, and it at least partially explains why snatch blocks are usually rated for such heavy loads.
 
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xxdabroxx

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They are like moving a pivot point on a lever from being 1:1 to 2:1. It is tough to wrap your head around though and the varying angles make it exponentially more complicated.


Something that would be interesting to see (although way tougher to do and likely of no real consequence) would be to use a weight of 300lbs in place of the winch so that there was always the same load. I'm not sure it would be different that applying 300lbs to the anchor point behind the winch though. The whole setup would have to be off the ground enough to hang a weight and that would add a 90D pull to the end as well. I say all that to get to the idea that it would be neat to see how much is pulled on each point with an equal weight being applied to the setup.

I think it might be easier to model on a fish scale size setup that could be done on a workbench. You could maybe even use heavy duty magnets on a steel bench to move around the anchor points and drop a weight off the side of the bench.
1565717793313.png
 
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mrblaine

mrblaine

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We should assume this is inconsequential for the purposes of the experiment.
The break away force to start the cart moving is less than 3 lbs. Once it is moving, the force to keep it moving very slowly is sub 1 lb. It has a couple hundred dollar's worth of casters under it so there is that.
 
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xxdabroxx

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No I mean you can think of a pulley like a lever in a sense. If a straight line pull was a lever it would have a ratio of one to one. One inch of travel at the winch would equal one inch of travel at the anchor point (winch being the immovable object). Whereas with a pulley in the system you have twice the travel on the cable to move the anchor point your same 1 inch.

Where it starts getting strange is when your anchor point for your pulley is not back to the winch and you end up with other than 180D turn at the pulley. Now your are using the winch to straighten out two legs of a triangle. Then the amount of force put on the pulleys anchor point is not getting twice the force the winch is pulling because the legs of the cable aren't moving the same amount.

1565727016692.png


1565727225280.png


1565727331628.png
 
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Sundowner

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No I mean you can think of a pulley like a lever in a sense. If a straight line pull was a lever it would have a ratio of one to one. One inch of travel at the winch would equal one inch of travel at the anchor point (winch being the immovable object). Whereas with a pulley in the system you have twice the travel on the cable to move the anchor point your same 1 inch.

Where it starts getting strange is when your anchor point for your pulley is not back to the winch and you end up with other than 180D turn at the pulley. Now your are using the winch to straighten out two legs of a triangle. Then the amount of force put on the pulleys anchor point is not getting twice the force the winch is pulling because the legs of the cable aren't moving the same amount.
Ah! Lightbulb moment! I get it, now!
 

xxdabroxx

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I think my graphics on the lower ones are incorrect. I believe my double lines only work when perpendicular to the cable. Let me rethink them a bit. It gets tricky. I'm thinking it's more along the lines of this. But I'm only looking at travel distances not necessarily weights. I think they are kind of the same thing but not really.

1565727894003.png