Mechanical Advantage, Part 3

Written By: Lance Piatt

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All right. The next mechanical advantage system in our progression is a five to one mechanical advantage system. And this is a simple five to one mechanical advantage system. So we’ve already differentiated between simple and compound. The last system that we showed was a four to one, and that was a compound four to one where you had a haul system, a two to one haul system pulling on a two to one haul system.

Now we’re back to a simple mechanical advantage system where we just have a pulley. We have multiple pulleys in the system, but they’re all moving in the same direction and they’re moving at the same speed. And that’s by definition, that’s a simple mechanical advantage system. And again, this is a five to one.

At this point in the discussion, I’m going to go ahead and omit the one from our T just in the interest of saving space. You can just assume that T is the same as one T. So again, I’m going to start at the haul strand where the haul team’s actually going to input the tension into the system. We’re going to assign T to that, and follow T down to our first pulley. The T enters on one side T exits on the other side, and we have two T.Basically transmitted through the first prusik to the load strand of the rope.

Continuing we follow the T that came out of the first pulley up to our first change of direction pulley. T goes in, T comes out. T continues down to the second pulley, T goes in, T comes out and another two T is transmitted to the main line.

We continue to the second change of direction pulley, T goes in; T comes out. This T’s transmitted down the line and it bumps into the first two T, and we move on to the second two T. So we have T, plus two T, plus two T , equals five T. We have a five to one mechanical advantage system.

And let’s go back and balance our equation. We have 1, 2, 3, 4, 5 Ts up at the anchor. And in this case, our anchor is carrying four fifths of the load. The other fifth of the load is being supported by the haul team. So we have five T on the anchor as well, and we balance.

And Now For Something You’ll Really Like

All right, the next haul system in our progression is actually also a five to one haul system. You’ll notice this system looks slightly different, though. This is an opportunity for us to talk about the third and final type of mechanical advantage system. This haul system is what is known as a complex mechanical advantage system.

Probably the most accurate way to define a complex system is it’s neither simple nor compound. Some defining characteristics are you have moving pulleys, pulleys that are actually performing work and moving a load that are moving in opposite directions of each other. And as you see this system function, you’ll see, I have two haul pulleys that are actually moving in opposite directions.

Some advantages of this complex five to one haul system over the simple five to one haul system are that I can actually build this with fewer pieces of equipment I’ve actually removed one pulley from the system.

So, if I have fewer pulleys and I want to build a five to one, I might be able to build a complex five to one versus the simple five to one.

Another advantage is that you’ll notice we’re pulling away from the anchor. So if we want to pull downhill, for instance, I might build this complex five to one, so I can actually walk downhill and use gravity to assist our haul.

Disadvantage is that it needs to be reset a lot more often. You’ll see the pulleys come together and they come together basically twice as quickly as the pulleys collapse in the simple five to one. So at some point I’ll have to stop and reset the system, which brings us to another point.

One thing that’s missing from all of these systems is a progress capture device. We’ve omitted the progress capture device.

Ordinarily. We would affix a prusik probably here below the first change of direction pulley so that any uphill progress that we make would be actually captured on that press. But we’ve omitted that for this discussion.

All right, moving on to analyzing our, our final mechanical advantage system, our complex five to one. As always, we start with our one T where the haul team is hauling. Then in this case, the whole team is hauling to in the direction of the load. One T goes in; one T comes out, and we have two T transmitted through this prusik. This T continues, T goes in, T comes out and another two T on our second prusik. T continues up and it runs into this two T, and we actually have three T and again, whatever goes into a pulley has to come out of a pulley.

The pulley, the pulley has to balance the tension. So now for the first time, we actually have more than one T going into a pulley and we have three T, three T comes out, three T transmits down the line to where our two T is waiting on the second prusik. We can add those together for a five to one haul system.

Balancing our equation, we have three T plus three T equals six T on our anchor. This is similar to our hauling a one to one through a change of direction where we’ve actually doubled the load on our anchor. We’re seeing a load on our anchor that’s greater than the result of our mechanical advantage. We’re actually seeing six T. The reason is we have five T on our load, and we are pulling an additional one T against the anchor in the direction of the load. So this five T is added to this one T and this also equals six T.

All right. So what we’ve covered here is basically an introduction to several different levels of mechanical advantage that we can construct in order to help us move rescue loads. We’ve shown everything from a one to one haul system, which is essentially us pulling on a rope, or pulling on a rope that travels through a change of direction pulley. We’ve showed a two to one, three to one, a four to one, and we’ve shown two different five to one haul systems.

There’s in the process of this demonstration. We’ve also seen that there are different types of mechanical advantage that range from simple mechanical advantage. to compound mechanical advantage. to complex mechanical advantage. Examples would be simple two to one mechanical advantage where we’re just pulling through a pulley that’s attached to the load, or that’s attached in the direction of the load, a simple three to one.

And then here we move to a compound four to one where we have two, two to ones haul, or two to one hauling on a two to one. So we have a mechanical advantage system hauling on a mechanical advantage system. That’s that, which makes it a compound mechanical advantage system.

And then our final system, this complex five to one haul system that has some benefits and some drawbacks. Benefits including requires less gear, and you’re able to pull downhill or pull away from the anchor if you want to. But the disadvantages that the pulleys tend to collapse more quickly on one another.

And then in terms of the team method, if you learn the basic roles of the team method and apply them, you should be able to analyze any mechanical advantage system, any combination of ropes and pulls and rope grabs and determine what the actual mechanical advantage is.

The basic roles of the team method, again, are assign one unit of tension to whatever the input is. Whatever the input, the haul team’s able to enter into the system in terms of amount of tension, and then follow the line continuously through the system, understand that each pulley doubles whatever amount of tension enters one side, that same amount of tension enters the other side and where that pulley is attached experiences doubled the amount of tension that entered the pulley.

 

Peace on your Days!

Lance

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