Understanding Mechanical Advantage by Brion Toss

If we are going to look at this in terms of lever classes, then we should also show that a pulley pulled by truck to pull a load on unanchored end as a 3rdClass lever(losing power but gaining speed/distance.

A pulley system worx by having to pull 5' out of each leg of the pulley system, to move the pulley 5' in the distance view to power. Or, if we have 5 legs of pull, each with 50# of input tension, will have a 250# potential in the power view.

Similarily, when a 100# climber pulls on 1 leg of their DdRT, they only have to pull down 50# because that 50# pull comes off of the 100# potential of the other leg, leaving 50# tension, that the 50# tension x distance can then move(in the power view/diagnosis)! Or, we can see that to raise the climber 5', (s)he must shorten each leg of line supporting 5', for 10' of line pulled to raise tehmselves 5'. Everything is Distance x Power, so the distance must be calculated in as power if in the input and not the output(distance).

Disatance and Power are reciprocals to a total sum. So, if there is no resistance, it didn't take any power,a nd only distance is achieved. But, if the load resists movement, then not as much distance is achieved, and more pressure/power is built up (as reciprocal to the distance not)
 
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If we are going to look at this in terms of lever classes, then we should also show that a pulley pulled by truck to pull a load on unanchored end as a 3rdClass lever(losing power but gaining speed/distance.

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Spyder, you're right. Riggers should understand how to reeve tackle to advantage and disadvantage and how to tell the differences between the two.

I'll see if I can post something.
 
Once't, we had a steep 100' hill (that had become nick named Hell Hill) to drag much up, for a repeating customer. The driveway was 50' before entering a steep curve to the street. We placed a rope on the load, to then reeve thru a pulley on the back of the truck, to then go to an anchor next to the truck hitch. We pulled the loads up a 100' hill with 50'run that way, and saved a lot of work in blazing Florida Sun. It had only half as much pulling power, but we had to go slow because the load was moving 2' for every 1' truck moved, so the load was going 2xTruckSpeed. A redirect was added at top of hill(but not tooo high) to keep line out of dirt. For heavier stuff, we used a small hood krab'd to pulling rope as nose of sled to keep from digging into ground on the washed out grade.

This became a standard tool, even without the hill; but perhaps several redirects to get our nylon cable laced from power to prey. The redirects could be manned to be released as the load arrived at that point to turn. It is better to set redirects too far, then just pull load to where CG isinline with new path, then release line from redirtect to turn.

So anyways, in the Equal and Opposite Forces , ying/yang view; we found mechanical advantage to suit. For, even in reducing the power (in trade for needed distance or speed), we found mechanical advantage(s)!
 
Spyder,that's a great story. Hell Hill, I like that. Of course I wasn't the one dragging the brush up the hill!

You made a good point too. Sometimes just because your MA is reeved to a disadvantage doesn't mean that it is a disadvantage for your work situation. Maybe its the only way you could pull from if you can't rig a redirect or have a poor lead on the line.

So you're right, you need to know the Equal and Opposite Forces , ying/yang and good and bad to MA in order to stay safe and productive in this industry.
 
Exact to the many times we set up systems to yard brush out of the right of ways. Truck for power, spars for purchase and redirects to zig-zag the loads around stumps and sidehill slopes.

I can't remember the exact make of the hood we used. Back when I first started with Sohner in 69. But when I first seen it I laughed and said, "you got to be kidding?", but when I seen how well it worked I ate my words.
 
Re: Understanding Mechanical Advantage by Brion To

We'd make sleds with branches, nice wide, upward turned nose on bottom branch, then cradle rest in there; build 4' high or so packed tight for apprentice loader, then stab criss-crossed rakes down into for stability to be dragged. Thing with redirects that need released on trail etc.; is guys would get lazy, especially ones that never did it all manually. Hard to convince them, even though just standing around; they had even more responsibility to make things go right, because we were using more power, so more responsibility.

Back to pulley classes;

Question(s): Is a climber lifting self in DdRT on pulley another class, or then what type of application of an existing class??? Is there a pairallell to non-flexible (wood, metal) leverage classes?
 
Re: Understanding Mechanical Advantage by Brion To

Boy, Ken, Chris, This is a real red hot thread.

All Joking aside, I'm sure you know how different the opinions are to the exact achievements of mechanical advantage there is in a particular system.

I prefer to keep it simple and just say, "there is mechanical advantage."

The same thing with knots. The names for them change between trades and geographic regions.

The jest of it all is the arguments don't amount to a hoot either way. But always good fodder for argument.

I suspect if the internet remains viable for long enough a universal understanding will eventually prevail.

But then it might get real boring too.

So what the heck did I even write this for?
 
Re: Understanding Mechanical Advantage by Brion To

I'm glad you wrote it Jer. I like the way you put things into perspective.

Sometimes we try to look at things and make them more complex than they should be, even with mechanical advantage.

I still try to work according to the "KISS" principle when I can.
 
Re: Understanding Mechanical Advantage by Brion To

You're a gem, Chris, and you too, Ken, for sharing and keeping things simple so others can understand.

And too for your temperament to avoid arguments on seemingly complicated rigging theory's.

Both of you are born teachers.
 
Re: Understanding Mechanical Advantage by Brion To

Well, actually to me; the weight isn't transferred so much as the distance (if sitting in it on a pulley and starting pulling yourself up). For even at stand still; there is 1/2Load on each leg of support. So, a 100# climber would have 50# on each leg of line. When (s)he pulls down on the friction hitch side\ dynamic side; it just makes it 50# x 4'=200 ft pounds effort(for example)work, rather than perhaps just hanging by arm rather than friction hitch on that leg of line('costing' 50# effort). Which then becomes 2' out of each of the 2 legs=4', that raises the climber 2'.

i think a class or a sub class of the lever classes is missing, that is denoted by this (and other) scenarios. A 1st class lever is the only class that the input(effort, bodyWeight) and output(work on load) are separated by the pivot. So, this means that the input and output flow in opposite directions; another unique aspect of only the 1st class levers. Therein, comes this oft overlooked use/ class/ subclass to me. Because the 2 moving points are in opposite directions, this type of system can manipulate the equal and opposite forces that are promised in all things. So, because this comes from 2 points to 1 this recursive setup gives a compounding action.

A pulley by itself is a 1stClass Lever, but the systems are broke into the 3 pulley classes by the position of that 1stClass Lever, the pulley. Of the 3 positions (inputEffort, pivot/anchor, outputWork on load); if the pulley is on the input we increase speed/ lose power like in a 3rd class lever (where the input is closer to the anchor/pivot) with input and outputs moving in the same direction. If we place pulley on the pivot/anchor position, we have a neutral 1st class lever, with input and outputs moving in opposite directions. And if the pulley is on the load, we have a 2nd class lever(with input further from pivot/anchor than load), with input and outputs moving in the same direction.

But, if we are hanging as ballast to a load, with pulley on overhead anchor/ 1st class position, and pull up on the rope going to load, we get our weight + 2xEffort on the lift/ballast on the load. With a foot cam, we can get 2xLegForce + bodyWeight, rather than 2xArmForce + bodyWeight.

Now, that has to be 1st class to move input of bodyWeight and passiveForce from effort of hand on other line moves down as it lifts up on load, but then can't be 1st class, because that effort hand on the load side is headed the same direction as the load.... The same can be configured on non-rolling levers (wood, metal etc.), to get 1xWeight + 2xEffort, but needs pivot between. Stand on one side of see saw, load just over pivot on other side, your bodyWeight pushes load up, and if you go to pick load up with 50# effort, you 'lighten' 50# off the load side of the seesaw, while 'increasing your bodyWeight' that is pushing up on the 50#(+ bodyWeight) lighter load by 50#... So your 50# effort gives 100# lift upwards as long as load is still on see saw. Once again with 1 pivot, we are moving inputs both with and against the direction of the load....

i've never been sure of de-scribing pulley systems in leverage class terms anyway. For, pulleys operate in 1 dimension only, as they are inline, not 'leveraged angle' devices. Now, bending across a tight line is leveraging to me, just like forcing across the long axis of a lever. A pulley's system increases leverage by adding another leg. But if we give a stool a 4th leg, do we say we have increased it's leverage?? we would only say that the leg is leveraged on the stool.. if the leg was at an angle, and thereby something changed direction as it progressed any movemeant. But, the example of a double use of force by capturing it's promised equal and opposite force and folding it back to work on the load exists in the non-flexible levers too.
 
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