3 pulleys - 8:1 MA

[SINGLE-JACK]

Bottom pic: with 2 parted bull rope & VT = 16:1 MA

 

[canopyboy]

Bottom pic: with 2 parted bull rope & VT = 16:1 MA

That picture link (http://www.arboristsite.com/picture.php?albumid=168&pictureid=548) doesn't seem to go anywhere. Maybe try again?

 

[asthesun]

Bottom pic: with 2 parted bull rope & VT = 16:1 MA

looks like a pretty short pull. why not get 2 triple sheave pulleys?

 

[canopyboy]

Now it works, nice...

 

[SINGLE-JACK]

Short haul

Isn't it true that two triples would only give a max of 7:1 IF hauling out against the load (ABOK#3219)?

Besides, I had the three pulleys - just wanted to see the max MA I could get with them. The pull is longer than it looks. At the top there are actually 2 pix with the mid-section edited out.

Since pull is directly related to rope length and MA, I figured at 8:1, for each foot of pull I'd need 8 feet of rope to "haul-out" plus all the rope running between the pulleys.

Two triples requires six lenghs of rope between them. I turned out that my experiment of using just three pulleys, required less rope, too.

 

[asthesun]

Isn't it true that two triples would only give a max of 7:1 IF hauling out against the load (ABOK#3219)?

Besides, I had the three pulleys - just wanted to see the max MA I could get with them. The pull is longer than it looks. At the top there are actually 2 pix with the mid-section edited out.

Since pull is directly related to rope length and MA, I figured at 8:1, for each foot of pull I'd need 8 feet of rope to "haul-out" plus all the rope running between the pulleys.

Two triples requires six lenghs of rope between them. I turned out that my experiment of using just three pulleys, required less rope, too.

well if thats what you already have thats fine. i guess the ratio for 2 triple sheaves would be less but i think the advandage of using a single long piece of rope instead of a few shorter pieces would outweigh the ratio difference. besides, if you have to have the extra pull, you could get 2 quad sheaves i guess. or you could do essentially what you have done except replace your clevis with a triple sheave and attach the pulleys to the rope with friction knots, this would also reduce friction since the rope doesnt have to slide over your clevis.

 

[SINGLE-JACK]

Well, it really doesn't matter. The experiment worked - didn't cost a cent. I had fun - got 8:1 with three pulleys and a lot less rope - 16:1, if I 2-part the bull rope. It's in a bag - probably use it someday.

More 'experiments' to follow.

 

[TheTreeSpyder]

It is about as good as ya can do with 3, it would have ma of 2 cubed = 8;as 3 sheaves (of 2lines) in such a series. But would have to pull 8' to get 1' of pull at that power, but could be hard to pull that 8', because when the closest pulley to your input hits the end of it's run, your'e done (the other sheaves would still be mid stroke)! So, if your pull line is 20' long, That only exerts 10' of pull on the next sheave, that will exert 5 to the last, that would exert 2.5' on the load. 2.5 x 8 = the original 20'; more for any stretch, anchor flex etc.

Because it is in this series, it can't be '2 Handed', but then with 3 sheaves; 8 is about all ya could due i believe anyway. The concept is similar to a groundie pulling you up at 1xEffort or you pulling yourself up at 2xEffort.

http://www.mytreelessons.com/climber%20lift.JPG

MTL : Pulley Systems.jpg

MTL: 2handing.swf

 

[SINGLE-JACK]

It is about as good as ya can do with 3, it would have ma of 2 cubed = 8;as 3 sheaves (of 2lines) in such a series. But would have to pull 8' to get 1' of pull at that power, but could be hard to pull that 8', because when the closest pulley to your input hits the end of it's run, your'e done (the other sheaves would still be mid stroke)! So, if your pull line is 20' long, That only exerts 10' of pull on the next sheave, that will exert 5 to the last, that would exert 2.5' on the load. 2.5 x 8 = the original 20'; more for any stretch, anchor flex etc.

Because it is in this series, it can't be '2 Handed', but then with 3 sheaves; 8 is about all ya could due i believe anyway. The concept is similar to a groundie pulling you up at 1xEffort or you pulling yourself up at 2xEffort.

http://www.mytreelessons.com/climber%20lift.JPG

MTL : Pulley Systems.jpg

MTL: 2handing.swf

Yup, that's exactly the way it worked. Pulled slack out of the bull rope. Used a VT with one pulley (2:1) to pull out more slack. Reset the VT, pulled more slack with two pulleys (4:1). Reset VT, pulled 8:1 'til the rope was tight as a drum.

With just three pulleys and the short bit of rope it was easy to handle without tangling or taking much rigging time.

Sets of three and four sheave blocks and all the rope was always a hassle to keep free of tangles, especially when storing.

This "seemed" easier. Anyway it's been a good exercise.

 

[canopyboy]

I had fun.

There ya go.

 

[Jeff_Cochran]

the problem in counting ma in a rigging system is most people count the line they are pulling on as an additional line. this line of thought is not true. in a crane you don't count the line going down the boom to the winch drum, to count it like you are counting your ma "16:1" system, would be to say on a three sheave block with no becket attachment that you are reaving seven parts or seven to one ma. this is not correct. the input line is not counted. to reave true 16:1 in your system you need to add two pulleys; one on the bottom sheave and one on the next sheave up to act as a redirect. here is a link that will explain it better.

 

[Jeff_Cochran]

i forgot the link http://www.youtube.com/user/khanacademy#play/user/AD5B880806EBE0A4/45/vSsK7Rfa3yA

 

[SINGLE-JACK]

the problem in counting ma in a rigging system is most people count the line they are pulling on as an additional line. this line of thought is not true. in a crane you don't count the line going down the boom to the winch drum, to count it like you are counting your ma "16:1" system, would be to say on a three sheave block with no becket attachment that you are reaving seven parts or seven to one ma. this is not correct. the input line is not counted. to reave true 16:1 in your system you need to add two pulleys; one on the bottom sheave and one on the next sheave up to act as a redirect. here is a link that will explain it better.

What you say is certainly true. However, The line I'm pulling on is also moving in the direction the load is moving so it does count to get 8:1 with the three pulleys. The load on that setup is a bull rope that has been doubled through a shackle (effectively another pulley). That gives another 2:1 resulting in an overall 16:1.

So, I've effectively got four "running" sheeves (ABOK #3209) in series. Each MA of 2:1 is multiplicative yeilding a 16:1 MA. What makes this possible it that I'm pulling horizontally, not "down the boom to the winch drum". Think of it as if I were up on the boom pulling up.

Anyway, it was just an experiment to see how much tension I could get on a line with absolute minimum gear. I actually did get 16:1 based on measurements. 16' of line pulled in resulted in 1' of load moved. But, like you imply, I did have to pull in the same direction that the load moved.

It's may not be very practical, but was a fun to do ... once.

 

[TheTreeSpyder]

If the last leg/ the one that you are pulling pulls on the load and not an anchor; it counts towards MA, as in any other leg of tension on load(inversely, an added table leg places less load on the remaining legs etc.). Otherwise the final leg is just redirect( if it pulls on anchor point/ not load).

Now, if we cam or prussick off to lock, then if the last leg is a redirect and lock point, we have same tension on lines in jig, when cam/prussick holding as when hand held. But, if the last leg of line is a pull on load and we place a self tended cam or prussick then when we pull each leg of line might have 1/5 load on them, but at lock of cam/prussik, we lose 1 leg of tension, so increase tension to 1/4 the same load. This can cause stretch, shift, drop in safety factor etc.

The 16x comes from 2 to the 4th. for this pattern of pulleys (also the maximum for a set of 4 pulleys); like the pictured is 2 to the 3rd. But, these designs give up travel, for amount of rope used and power achieved. Because, you can't use all the rope. Unless resetting prussicks/ cams, or just have 1 sheave extra pulling on like a zrig, to use the extra sheave to jump start against inertia, both your self and load moving to favor, then jump over extra pulley and pull straight on zrig at right time. But, in regular practice, with any speed needed, the tiered pulley systems give the most power, but 'cost' extra line (beyond what the power trade off delivers).

All these powers we speak of are just potentials; potentials that we never achieve. Part of the promise of the equal and opposite pairings, is that at each machine point/ change we break into 2 reciprocals: the efficiency, and the inefficiency/loss. Every machine change will have a loss/ there is no perpetual motion machine, the magic Kennedy bullet is till not flying etc. The losses are from frictions, and they can geometrically increase on each other just like the potentials. All lines (including pull line if pulls on load directly) are assumed to be inline/ at Zer0 degrees deflection, if wider there is more loss, any stretch etc. All ways best to have too much power, and trim it back by gentle giant, staying within your power band etc. IMLHO.

MyTreeLessons.com/Marlinspike Sailor.htm

MTL:Marlinspike Sailor Rig

Some of the more counter intuitive applied:
MTL:Force Relationships

 

[Jeff_Cochran]

do me a favor count how much rope you pull for how much work is done. that will give you the ma. it explains this in the link.

 

[TheTreeSpyder]

If a leg of line is directly connected to load, that leg must be shortened to move load. So, if 5 legs connected to load, and want load to be moved 1', must take 1' from all 5, or give up 5' of input distance per 1' of output distance as reciprocal trade-off to the 5xEffort gained. This is true even if pulling one of those legs by hand etc. There is no free ride, to get 5xEffort, must input 5xDistance of output; must retain same 'volume' of power of distance x power as it's quanity (picture a rectangle volume of lenght for distance and height for power, that volume msut be same, even if 'wider'/'shorter, or narrower/taller; must equal the same 'volume' of work,energy).

 

[SINGLE-JACK]

"on rope" confirmation

Just got my copy of "On Rope" by Bruce Smith & Allen Padgett. The 'three pulleys 8:1 MA' is shown in Figure 7-9 (p187) and again with more technical detail in Figure 10-24c (p243). I knew I wasn't plowing new ground but it is nice to know that I got it right. It's a great book. I could use an update - there's stuff I've gotten off these forums that should be in there. However, if you don't have a copy - SHAME!

 

[treemandan]

There ya go.

The Dan abides.