mechanical advantage IQ

[igetbisy]

hhh

 

[igetbisy]

oops, just figured out how to get that image into post, and submitted instead of previewing. so here's the text for it.

how many of us can calculate the MA of the tackle systems in the image, mabye after a little of what we do best here, (debate amongst critics) we will come to a final agreement that everyone understands and mabye there will be a few who will get to learn a little about compound tackle, and MA.(mechanical advantage).
i'll put it in this post, so you dont have to go back.

 

[Tom Dunlap]

Take a look here:

http://www.alberta-ck318.freeserve.co.uk/tackles.htm

for a good description of MA.

Tom

 

[Kneejerk Bombas]

I'm going to guess the advantage is about 9 to 1.

I find if you set up the system and measure how many feet you have to pull to get the load to move one foot, gives you a close mechanical advantage. Of course we're ignoring friction and the angle between the to sets of blocks.

 

[Tom Dunlap]

The theoretical MA would be 16:1 but Mike brings up the discounter, friction. I wonder how much effecieny is lost because of rope stretch.

I we were with Jack Aubrey on the Surprise, http://www.wwnorton.com/pob/pobhome.htm we would be using blocks carved out of elm instead of bearings and bushings. The lines would be three and four strand natural fibers. Power would be pure muscle and maybe the capstan.

Tom

 

[John Paul Sanborn]

Tom, Joey Cornel is working on the Constelation on a semi regular basis right now

 

[Kneejerk Bombas]

Tom, do you think the angle that the second set of blocks is pulling at changes the MA?

 

[DadF]

I gave up on math a long time ago but it would seem to me that as the load rises the angle would increase thereby reducing the MA ?!??!?!

 

[Tom Dunlap]

Yes, the effeciency decreases.

Simplify the setup, eliminate the MA system and see it as a two-leg sling. The wider the angle the lower the load on the anchor points.

Tom

 

[NickfromWI]

Originally posted by John Paul Sanborn
Tom, Joey Cornel is working on the Constelation on a semi regular basis right now

Me and Karina, too!!!

love
nick

 

[Erwin]

Ignoring the friction and angle issues, I thought the theoretical MA should be 16. Assuming load on set B is 400LB then the pull on set B or the load on set A should be 100LB. Then, the pull on set a will be 25LB. 400/25=16. It's been a very long time since I did this kind of puzzle. I might be well be wrong, just to get some more discussion. Erwin

 

[John Paul Sanborn]

Originally posted by NickfromWI
Me and Karina, too!!!

love
nick

Have you worked with Joey? Is he the incorigable flirt with Karina and any other female in the area.

He cracks me up worse then Ox!

 

[Kneejerk Bombas]

So if I understand, the red arrow in this picture shows an angle that would increase the MA as the angle decreases, because it starts to add lift as it gets less than about 90 degrees.
The angle shown by the green arrow is much less important because it's affects are after many of the blocks.
Sound right?

 

[Mahk]

It's a compound system, but there are four parts of line going to and from each of the moving blocks (block B that is holding the load and the lower block A). Ignoring friction, and the fact that not all of the lines are parallel, this gives an MA of 16:1 (4 lines at block B with the load times 4 lines at the lower block A).

Mahk

 

[Tom Dunlap]

Maybe this helps or maybe it confuses:

http://www.climbingmadness.com/tips_tricks/tips3.htm

Mahk is right, look in Section 3 of this manual for the same setup:

http://www.adtdl.army.mil/cgi-bin/atdl.dll/fm/5-125/fm5-125.htm

Tom

 

[arbor01]

The easiest way to decipher MA is to determine the number of parts of rope acting on the moving blocks.

 

[Kneejerk Bombas]

Ah... "Count the number of lines supporting the load...in counting, include the fall line if it leads out of a traveling block."

I still think the angles I drew are important.

 

[NickfromWI]

This is something that I'd like to be much better at.....looking at a system and determining the MA. There are guidelines to follow, but when I look at a funky/complicated system, I just get lost.

So if I'm up in a tree, hold the tail of my rope so a big loop (actually a bight) is hanging down, and the person who happens to be working the ground at that time (how's that for pc?) clips a carabiner to that bight then clips my chainsaw to that carabiner, and I start pulling the tail end up, that's a 2:1, right?

Now If I girth hitch a sling around a nearby branch, hang a little pulley off that sling, run the tail of the rope through it and have the person on the ground pull it up, it's still a 2:1, right? The pulley is merely a redirect?

Before I go further, is this right so far?

love
nick

 

[Lumberjack]

Yes nick you are right on both accounts.

Carl

 

[Tom Dunlap]

Nick,

That's whats called a Double Whip Tackle, DWT.

Did you see the nice little animations on the page I linked above?

Tom