mechanical advantage IQ

[NickfromWI]

I just checked it out. Yep definately a Double whip.

So what's the difference between the double whip and the Gun tackle. They look identical to me.

love
nick

 

[Lumberjack]

IMO


A gun tackle offers a 3:1 MA. According to the chart a doube whip offers 1.67 to one, or 2:1; while the gun tackle offers 2.5 or 3:1.

They look similar however.


I may be wrong, but I don't think so. Correct me if I am.


Carl

 

[xander9727]

I say 16:1.

 

[Lumberjack]

It is rigged 16:1. However you would have to multiply the second set by the cosin (adjacent over hypotenus) of the angle. You would get a decimal. You would multiply the effeciency of both systems first, then the cosin to the 2nd set, then the 2 sets together. Probably around 10:1-12:1 i would bet.

Carl

 

[xander9727]

You would only use the law of cosine for the second half of the equation. The first MA would be four to one. You would multiply this times the product of the second four to one MA times the cosine. This would of course change as the load was raised so calculus will be necessary with the limits set from the starting angle to the maximum lift angle. You then could figure the "True MA" at any point in the system.

I think that 14-15 to one would be a safe guesstimate.

 

[NickfromWI]

In what instances is it important to know the MA?

Could a person get by with guidelines like "the more pullies, the more rope I have to pull, but the pullin' will be easier." If I pull and I ain't gettin what I need, add more pullies!

I'm gonna work on this...I wanna get good at it. I gotta start at the bottom and work my way up, I guess.

love
nick

 

[Lumberjack]

Originally posted by xander9727
You would only use the law of cosine for the second half of the equation. The first MA would be four to one. You would multiply this times the product of the second four to one MA times the cosine. This would of course change as the load was raised so calculus will be necessary with the limits set from the starting angle to the maximum lift angle. You then could figure the "True MA" at any point in the system.

I think that 14-15 to one would be a safe guesstamate.

I was sayin remove friction from both tackles first. Then do the cosin to the angled tackle (because it effects its 4:1's effectiveness), then put them together to get your final MA


Like you said tho the MA would decrease as the load was lifted because of the increased angle. I woulda thought that the MA would be lower, with the added friction and all.

I aint gone that far in calculus yet. We are doin differentations of graphs now... real easy stuff.


Carl

 

[xander9727]

Originally posted by NickfromWI
In what instances is it important to know the MA?

Could a person get by with guidelines like "the more pullies, the more rope I have to pull, but the pullin' will be easier." If I pull and I ain't gettin what I need, add more pullies!

I'm gonna work on this...I wanna get good at it. I gotta start at the bottom and work my way up, I guess.

love
nick

It is important to know the MA when you are trying to move, lift, etc. something and you can only apply a limited amount of force. e.g. You want to lift a branch up off of a roof and you can't get a tractor, truck, etc. in the back to pull and you don't own a GRCS or a Hobbs device to lift with. You use your weight charts and figure out that the branch weighs approximately 350 lbs, and you only have one groundie helping you. In this case MA is necessary to safely do the job (unless the groundie is one of the Strongest Man finalist). If you figure your groundie can safely pull 70 lbs then you need to calculate how much MA you'll need to lift the load. In this case you would need 5 to 1.

Tod

 

[Lumberjack]

Originally posted by NickfromWI
In what instances is it important to know the MA?

Could a person get by with guidelines like "the more pullies, the more rope I have to pull, but the pullin' will be easier." If I pull and I ain't gettin what I need, add more pullies!

I'm gonna work on this...I wanna get good at it. I gotta start at the bottom and work my way up, I guess.

love
nick

That is what I use plus some extra.

I keep a 6:1 rigged in a box for heavy stuff like pullen over back leaners. A 2:1 is also easily rigged. However I can combine the two and get 12:1 which is enough for almost anything or redo the 6:1 and make it a 5:1 with a 4:1 add in for 20:1. Then i could redo my line to the load to go through a large block and have up to a 40:1. That would be enough to get me through most stituations I would think.

Using MA is awsome. I would rather pull slack than strain too hard.


Carl

 

[NeTree]

My MA equation:

"Can ya lift it?"

"Nope!"

"Hey Rick, bring in the crane!"

Done.



Seriously... this is WAY cool.

 

[xander9727]

Originally posted by netree
My MA equation:

"Can ya lift it?"

"Nope!"

"Hey Rick, bring in the crane!"

Done.



Seriously... this is WAY cool.

Netree,
I want a crane too......

Maybe next year, this year it's a new chipper. Thinking of either Bandit or Morbark.

 

[Lumberjack]

For MA I have 2 double sheeve CMI pulleys (4") rated to 25k, another CMI sigle sheeve (4") rated to 16k, and a CMI 2" rated for I dunno 10k?. With those I can get a 5:1 with the doubles. I can add the small CMI inside and get another 6 for 6:1. I can put the large single CMI outside making a 2:1 with it to the load, then put the 6:1 on the tail for 12:1. Then I can take out the small CMI pulley, make 1 2:1 with the large single with the 5:1 on its tail, with a 2:1 on the 5:1's tail with the small CMI for 20:1. Then I could rig in a rigging block on the load line to make a large 2:1 with the load line and have 2,4,10,12,24, or 40:1 I think, but having to pull 40 foot of slack to move the load 1' wouldn't be too fast and would use alot of rope to weave through the blocks.


Carl

 

[Tom Dunlap]

There are several layers of limitations with MA systems. It is good to have a basic understanding of the math too. Otherwise you can build up a system that overloads the anchor point.

Knowing the loads will set the size rope and blocks you build on. Harken has some good information on building MA systems.

A rule of thumb for calculating the pulling power of the big one on the crew is to use a maximum of 80% of body weight. That's with optimal foot traction and a pull that is fair to the input.

The article with the animation talks about the limitation of compound tackles compression speed. It took me a couple of reads to fully understand what they meant.

When I was on the HMS Warrior in Portsmouth I saw that they had the gunports rigged with a 2;1/2:1 system. At first I couldn't understand why. It seemed simpler to rig a 4:1. After looking for a while I realized the the compound system could be collapsed a lot quicker which meant the gun ports could be left closed longer. Very clever.

Tom

Tom

 

[Lumberjack]

Yea, I put the big guy on the far side of the tree/ anchor so he can use his legs to push. That helps alot. After that get a smaller guy to make a wrap (if allowed) and have the big guy sweat the tail of the MA, which, depending on the length of the tail, could be very powerful, but painfully slow. I used a 6:1 to pull a leaner back away from the house. Wasn't easy to say the least, but the sweating trick did it for us. Shoulda added a 2:1 and have the 6:1 on the tail, but we got it.


MA to me is more chineese rithmic than SRT. But that is just me.

Carl

 

[xander9727]

Lumberjack,
Do you use a safety stopper when using MA? By safety stopper I mean a friction hitch or a cammed rope device so that if someone slips, falls, lets go, etc. the load won't fall. These are especially helpful on long or heavy pulls to allow guys to rest or reposition. Just remember to place it towards the running end of the system so the device isn't subjected to the full load.

 

[igetbisy]

answer

 

[Lumberjack]

Originally posted by xander9727
Lumberjack,
Do you use a safety stopper when using MA? By safety stopper I mean a friction hitch or a cammed rope device so that if someone slips, falls, lets go, etc. the load won't fall. These are especially helpful on long or heavy pulls to allow guys to rest or reposition. Just remember to place it towards the running end of the system so the device isn't subjected to the full load.

Yes on pulls where it is needed I either put one on the last leg, so the pulley minds it, or have the smallest guy take a half wrap around the anchor if permissable.

So yes.


Carl

 

[Matt Follett]

Hey I missed most of this... That was fun.
MA is wonderful, and being able to build 5:1's, 10:1's is great... but somebody asked the question of why is it important to know, and then Tom D brought up perhaps the most important point which we (the tree industry ) really need to recognize. As we add all these tools to our arsenal of tree section removal, we need to remember the tree!

I meant to post this 'incident' back when it happened, but forgot.

This summer while doing a "oh yeah we'll be done by lunch" take down on a Gliditsia we pulled out the pullies to tip tie and lift the larger limbs off the garage... one climber was removing one side of the tree (no rigging) while another was doing the technical stuff.

to make a long story short... the anchor point (tree) for the lift failed... when we had a 'pretty big' piece in the process of lifting... it got pretty ugly fast. Most of the 'pick' landed in another part of the tree and got hung up before it hit the garage roof, the climber was tied in on another part of the tree, and managed to escape the crashing pieces.

In the end no one was hurt, and no damage done to property, but we have re-thought what good only tough Honey locust can handle.

We only had a 5:1 set up, but two of us on the ground pulling for lets say an estimated 1000 lbs of force maybe more (good footing) take this up the line and down to the piece that's an easy 2000 lbs at the block... KA BAM!

I'll try to draw an acurate pic and post it following this to theorize why it failed the way it did.

But the point is no matter how strong our gear is we are still working with a relative unknown, The tree, we really only have experience to base our decisions on (well last week the Silver Maple held up, this oak should too..........)

 

[Matt Follett]

In the image...

The peice removed on the left, was by the other climber working the other side of the tree... After the limb was removed we did one more rig off the anchor, while that climber decended. (Before that limb was removed we had done several lifts off that point, all successful)

We did the next big one and the tree split down the red line and hinged over... the limb got caught up in the rest of the tree and stopped, but still ugly.

I think the loss of cohesion between the fibres further up allowed the limb to split off, the crotch did not fail in any way. Had the other side still being there... I don't think it would have failed.

Anyway, lesson learned?! watch how much you load with fun toys.

 

[NickfromWI]

Xander, in the situation you mentioned, it's not so important to be able to look at the system and say, "Hey that's a 6:1" is it. The idea I was suggesting....netree hit it right on head....almost. If mr groundie tries to lift and it doesn't go, then put more pullies.

However, I still think it's important to know this stuff. Just wondering when it's crucial to know it.

love
nick