People think pulleys increase pulling power.

#93
What helps me in understanding this phenomenon of Work and Load with pulleys and in what scenario are you providing mechanical advantage.

When you have 25 feet of line going to an anchor 25 feet away. The vehicle will move forward 1 inch for every 1 inch of line pulled in by the pulley.

When you have 50 feet of line going to an pulley anchor 25 feet away, and then back again to the an anchor on the vehicle. The vehicle will move forward half an inch for every inch of line pulled by the pulley. Whenever this is the scenario there is mechanical advantage created.
The problem I had was counting lines and the power coming from an external force. With the power inside, like a winch, it becomes a pulley, its line is part of the pulling force and a multiplier.
 

DaveInDenver

Expedition Leader
#95
Can you run half the engine?
Maybe half the battery or alternator. There's a minimum draw for a winch, which is it's unloaded speed. That's sometimes low enough that your engine's alternator might even keep up indefinitely. Under full load a winch is going to drain your battery pretty quick and is going to heat up very fast.

So you want to be closer to the unloaded 90A rather than the fully loaded 350A.

We could introduce the concept of duty cycle but since it took 7 pages to agree the ancient Greeks and Babylonians were right doing that might cause mental meltdown.
 
#96
How much mechanical advantage does an endless chain provide?
Dunno offhand. My 1000lb Timken Hoist seems fairly deep ratio, probably around 20:1. (that picture is same as my hoist)
One would need to measure diameters or count teeth of its tandem chainwheel to calculate.
 

DaveInDenver

Expedition Leader
#97
Dunno offhand. My 1000lb Timken Hoist seems fairly deep ratio, probably around 20:1. (that picture is same as my hoist)
One would need to measure diameters or count teeth of its tandem chainwheel to calculate.
That's probably in the ball park. The 1 ton hoist I have seems to be 18:1 by my estimation. It's not a single chain differential like that but rather just a newer geared one with a chain loop, but I suspect ultimately the required effort would be similar anyway. Heavily loaded it still not easy to move so it's clearly rated to hold that much weight rather than move it without significant effort. But OTOH too much reduction and it takes forever to raise and lower something that isn't 2,000 lbs.
 
#99
The snatch block can be though of as a spinning lever.
Spinning Lever.jpg
If the Snatch Block is rigged as a class 1 lever, you don't get a mechanical advantage.
class 1.jpg
If the Snatch Block is rigged as a class 2 lever, you get a mechanical advantage 2:1.
Class 2.jpg
Hope this helps
 
The snatch block can be though of as a spinning lever.
View attachment 440660
If the Snatch Block is rigged as a class 1 lever, you don't get a mechanical advantage.
View attachment 440661
If the Snatch Block is rigged as a class 2 lever, you get a mechanical advantage 2:1.
View attachment 440662
Hope this helps
This is how I always saw it but in the 1:1 If you run it back to the jeep it becomes 2:1. The tree pulley is change of direction and the winch on the The winch becomes a pulley carrying the load. This what has hard for me to see.
 
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Fireman78

Expedition Leader
Have you heard about the new Yeti Axe with a 4:1 mechanical advantage? It’s only 379 bucks but I’m holding out till it comes with a cup holder.


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rickc

Adventurer
This has been entertaining; lots of good points but I think Robert is the only one that answered the OP's starting question (thread page 5). If simply pulling yourself out of a ditch/up a hill whatever using a tree/truck as a base it's always best to run the cable out as far as you can, leaving at least 5 or 6 wraps on the spool because this provides the most mechanical advantage from the winch. If you are unable to run the cable out a good distance then the alternative is to use a single pulley at the base and connect the hook end back to your vehicle or another base. The pulley is not providing mechanical advantage itself but it's allowing the winch to pull harder due to increased efficiency.

The amount of cable on the spool increases/decreases working load depending on amount of line on the spool. Your winch is rated on the first wrap of the spool but obviously you can't safely pull on that wrap, you need a safety factor. Each successive wrap decreases your pulling power but that doesn't change your mechanical advantage, it only explains why you may need to increase your mechanical advantage i.e. add more pulleys into the system to make up for lost power- which will obviously require more line. This is why most recommendations are to go at least 1.5x your vehicle weight.
 
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