This drawing is incorrect. A single pulley only changes the direction of force. Not until you add a second pulley does it cut effort in half..
People think pulleys increase pulling power.
- Thread starter MOguy
- Start date
billiebob
Well-known member
wow
billiebob
Well-known member
2 blocks achieve 3 to 1Can we discuss compound systems using 2 blocks to achieve a 4:1system
Sent from my E6810 using Tapatalk
Last edited:
billiebob
Well-known member
Exactly.Here we go again. This statement would be true IF you were only using the pulley as a direction changer and did not hook the cable back to the rig. If you run the cable from the winch through the pulley and to another fixed object like another tree, then yes there is no mechanical advantage.
However, by running the cable from the winch through the pulley and back to the winch (bumper) then you gain a mechanical advantage of 2x. The winch drum itself is considered a single pulley, so when used by itself it is a 1x force multiplier. Adding a second pulley (the one attached to the tree) and attaching the line back to the same point of the first pulley gives you a 2x multiplier.
Look at this image:
The first one with a single pulley is representative of a winch attached to a vehicle and the "load" being the tree or rock or whatever. Something to keep in mind is that if your vehicle was locked in place it would be trying to move the load (tree, rock, etc) and not the vehicle. The reason a winch works for a recovery is the the load it is pulling on has a greater resistance (weight, resistance to force, whatever) than the vehicle the winch is mounted to. Think of a towtruck, it weighs more than the vehicle it is pulling and has more resistance so the vehicle it is pulling onto the bed is what moves and not the tow truck itself. The same thing happens when you choose an anchor point for the winch cable that does not have enough resistance, so it ends up moving instead of your stuck vehicle. Pick too small a tree or a loose rock or too soft of sand/snow and you move the load instead of your vehicle.
Since the first pulley is actually the winch drum, we can easily see how a pulley attached to the load with the cable run back to the same mounting point as the winch (or first pulley) you obtain a 2x mechanical advantage.
If you then add a third pulley to the winch mounting point and then run the cable through that back to the "load" (tree, rock, land anchor, etc) the you obtain a 3x mechanical advantage.
I think this is everyone's hangup that doesn't agree, they aren't viewing the winch as the first pulley, and/or they are viewing the load as the vehicle, when it's actually the anchor point (tree, rock, etc) that is the load and we're just counting on the vehicle moving more easily than the anchor point. The force being applied to the cable and load (anchor point) is being provided by the winch motor via the first pulley which is actually the winch drum.
I hope this helps.
Sent from my SM-N950U using Tapatalk
When winching, the pull is at the dead weight.
1 pulley back to the vehicle cuts the effort in half. 2 lines.
2 pulleys, 3 lines, cuts the effort to one third.
Another prespective.
If you wind on 10' of cable and the vehicle moves 5', 2 to 1.
Wind on 15' and the vehicle moves 5', 3 to 1.
Last edited:
The winch drum is not an extra pulley, it's just where the line is stored. It pulls what it can. If you are pulling your own vehicle and it weighs 1000 lbs(1000 lbs effort to pull), let's say, just because you run your line out to a tree and back to the vehicle does not reduce the effort. the first pulley always ONLY changes the direction of force. Add a send pulley next to it (on the vehicle), which is a 2 pulley block, then you cut effort in half(500 lbs).
MOguy
Explorer
YES it is IF the winch moves within the rigging it will create mechanical advantage. I couldn't understand this until I did my on experiment and say it with my own two eyes. Even then I couldn't see it at first, it took me two attempts and 76 posts but I finally got it. Thanks to all those that stuck in to help me. Two feet of cable moved and my jeep moved one foot. A pulley within the system will create mechanical advantage, a pull on an anchor point is change of direction.
Last edited:
The winch drum is both the first pulley AND where the extra line is stored. The pulley on the tree is the second pulley. If you stop thinking of the winch drum as merely a place to store the rope then you'll get it. The winch drum is a powered pulley. Instead of applying the force at a point past the first pulley, the first pulley itself is the power source here. Same thing with a windlass (google it), which generally doesn't always store the rope on its powered pulley. Just because it is the place power is applied, doesn't mean it is not a pulley.
Seriously, please stop dragging this ridiculous argument out. Do the experiment yourself that has already been discussed on here before trying to act like you know what you are talking about.
Metcalf
Expedition Leader
No
By adding a single pulley AND connecting the line back to the vehicle, you cut the force required in HALF.
For every 1 foot of movement ( either vehicle toward the anchor or the load towards you, the winch will be spooling 2 feet of cable.
Buliwyf
Viking with a Hammer
Pulleys are nothing more than reduction gears. More pulleys, more torque, less speed. Ya'll are over thinking this.
If the object being pulled, is traveling slower than the line going into the winch, you've increased pulling force on the object. Just watch with your own eyes.
And the more cable on the drum, the less force the winch can apply. The winch has more leverage when you use as much line as possible.
If the object being pulled, is traveling slower than the line going into the winch, you've increased pulling force on the object. Just watch with your own eyes.
And the more cable on the drum, the less force the winch can apply. The winch has more leverage when you use as much line as possible.
Buliwyf
Viking with a Hammer
billiebob
Well-known member
wrong
billiebob
Well-known member
if you don't understand, no one can explain it
count the lines, not the pulleys.
one line, no reduction
two lines, cuts the effort in half
three lines, one third the effort.
MOguy
Explorer
I didn't understand, know I have a a better understanding.
And it isn't all about lines, where the pulleys sit is important.
It doesn't matter if the line goes back to the source of the pull.
The winch doesn't do anything except pull(it's performing all the effort).With one pulley the winch will have to pull a 1000 lbs wherever it's attached.
Now add a pulley at the vehicle, run the line out to the tree pulley, back through the vehicle pullley and attach at the tree, you now cut the effort in half(500lbs).