5x and 3x rigs together can give 21x or more

[TheTreeSpyder]

http://www.mytreelessons.com/flash/pulley21xRig.swf

This goes on to show more than 21xEffort; so that a 100#Man with a 50#ArmPull has the potential to pull 3700#. As any potential thus, it will not be reached, for as the multipliers of the full efficiencies of the pulleys compounds, so does the their reciprocal inefficiencies become compounded. Like 7 sheaves in series will drop you down to about 75% of potential, even if the sheaves are a fairly high efficiency like 95% each.

For, there is no 100% efficiency at a point of conversion(pulley, pivot etc.), or there would be perpetual motion. So, at a conversion point, everything is broken into it's efficiency and it's reciprocal inefficiency (as cost of the conversion).

 

[JeffL]

Awesome! Poor mans lifting device.

 

[oldirty]

cool man. thanks. awesome info.

 

[pdqdl]

There is a BIG drawback here!

The multiplication of force by pulleys is well understood. Unfortunately, the math of multiplication of force also means that for 21x force you must move 21 times as much rope as final movement by the load.

So to move a load 1 foot, you will need to pull in 21 feet of rope. Unless you have a LOT of room between your pulleys, or you only need a very small amount of movement, you had better pick up a better method.

I would recommend a windlass on a pulley system: this is essentially a rope winch or a GRCS applied at the end of several pulleys. Less rope required for equal power.

 

[TheTreeSpyder]

i guess i might have assumed that the exponential increase of pulley systems was less understood, than the distance reciprocal.

i'm not really focused on making a 32xEffort + 21xBodyWeight rig, but rather use that as an example of what decisions can be maid on the fly to maximize something. The big numbers and overdoing the theory is jest to magnify it for closer view. Also, the interchangeability should be apparent to make like a transmission that you can start fast reeling in line, then add whatever setup to that to finish off the work with a slower, more powerful strategy. If you just have a pull on a 5xRig and reach down and pull up yourself at that 3xPoint, you can get 5xBodyWeight + 8xEffort to finish pre-tensioning etc. Even for a lil'hero of 100#BodyWeight and 50#Pull, that is 900# potential without orchestrating impacting with those forces. As a transmission that is 5xWeight to start faster, then add 8xEffort to finish up slower. Switch gears on that transmission like going from spinning the shaft on a screwdriver(for speed), to spinning by handle when getting tougher.


If that all don't get it; lock it all off and bend it; or just lock off tail, and bend it. Look at the inline 'leveraging' of the pulleys as increasing the rope's resistance to bending, then bend that rope that now resists sideways force. Much higher return is now possible. Same theory applied to line, can be then slipped thru bollard, capstan, Porty etc. to pretighten line/ lift. As Brion Toss explains as 'Sweating' or "Moving Heavy things" as 'Swigging' more purchase from a line. (see attachmeant),

Also, made this: Spanish Burtons - Old Worlde Compound Pulley Systems

 

[moray]

...So to move a load 1 foot, you will need to pull in 21 feet of rope. Unless you have a LOT of room between your pulleys, or you only need a very small amount of movement, you had better pick up a better method.

This is a very good practical point, and the reason on the old sailing ships you see lots of big standard blocks and tackles with 3 or 4 sheaves in each block. They are not the most efficient way to get high MA, and they are quite lossy because they use so many sheaves to achieve a given MA, but they can't be beat for compactness, simplicity, and versatility. One rope, one rig, and two connection points. You can easily relocate it anywhere. I have a small rig in my garage with 4 sheaves that I use for experiments and sometimes for pulling a tree. None of the alternatives I could think of would fit in my garage and still give me a useful pulling range.

 

[turnkey4099]

I've seen the eskimoes pulling whales on shore using multi-sheave sets pulling on another multi sheave set. Just a line of eskimoes walking along pulling on the rope. Must move the whale about a foot at a time before resetting.

Harry K

 

[John464]

Thanks for sharing. Love your site!

 

[woodchux]

It seems to me like the prussics would slip...

 

[Fireaxman]

Thanks for sharing. Love your site!

+1. And, Glad Bob is feeling better. Continue to pray for continued recovery.

 

[TheTreeSpyder]

Thanx, superBob is home and out of danger mostly, still subject to 'biological fallout' from the ordeal (of both dis-ease and cure!).

The prussics could slip at some point; but please notice that the prussics only bear a percentage of the total output. Whereby the top prussic has 3xW + 4xE, and the lower 2xW + 4xE. Or, with our 100#Body Weight and 50#Effort example 500# on top prussic and 400# on lower.... Same with hand pulls, less energy needed by more powerful leveraging and splitting inputs into 2 parts (to match same load resistance with less leverage and 1 input) The divided input prussics (instead of all the input to match workload requiremeants coming from a single pointof hand and/or prussic, cams etc.), inset inside the compounding is part of the beauty of the strategy....

i really don't expect everyone to build this for every occasion. But, hopefully they can look at their present tools differently, and what decisions can be maid to maximize in 1 direction or the other (power or distance) to suit. The example was chosen to exemplify the the principals as tools themselves, not the pulley systems per se. A common tool of some arborists is a 'pre-wired' 5xRig. With just that you could feed into it body weight to pull slack, then immediately drop to 'low gear' and tighten the rest of the way with 5xW + 8xE. Just a different range of options. Also, splitting the input forces into bodyWeight and Effort, allows to recognize impacts of hitting hard with both suddenly, or holding a load 'at bay' with the bodyWeight input, and then impacting the Effort input into the equation etc. suddenly

One application is getting your bodyWeight off of a load being pretightend (if bodyWeight is consequential). Then, even hanging bodyWeight on control side of rigging (against load). Notice we have a 2xBodyWeight change in scenario, lifting up on load with bodyWeight as opposed to pressibg down on it. Then, reach down onto load side and pull up, gives 2xEffort to help pre-tighten. Now if this isn't 'consequential' to load, you should climb up some and try to get some rope length to pre-stretch with that force (and perhaps 'spring' secondary support). If your efforts are 'consequential' to the load, you can reach out further than the hitchpoint for more leverage also. Multiple supports also then allow sweating line between...

Some more old Worlde Compound Pulley System on Ship. Notice how the smaller system is piggybacked on when needed. It could be anchored to the side of the ship, but the choice here was to 'close the system' more and trap more of the promised Equal and Opposite forces created.

Certainly rotating input allows you to still input distance and stay in same point, where a 'linear leverage' input of a pulley system demands you to move from a position to input distance. Bollards and capstans are great ship tools too!