I don't understand how this holds
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- čas přidán 26. 03. 2024
- Does the Voodoo hitch have a mechanical advantage? Does it hold force? How?
/ whitewaterpirate
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"Mechanical advantage only exists when something is moving"? I guess that all that time I spent studying Statics was all fictional!!
Well no, but actually yes
Yeah, I'm not entirely sure what point he was trying to make there. Mechanical advantage exists in a static system, but you don't achieve anything. A force only does work if it is acting over a distance. Maybe that was his point?
Sometimes mechanical advantage can be useful to hold a force more easily, but in that case you are much better off with friction rather than a pulley system. That's how a massive ship being held by one man holding a rope wrapped around a bollard works or how a tensionless hitch works.
Don't you mean "frictional"?
There is no static system. force changes, something! Moves. Macroscopic or mikroskopic. In relatively stretchy ropes if turningpoints in this setup don't move, no force change...
M8. Math is only a snap shot. Math is stationary. Math is not a running simulation of the real world.
Sailor here. My understanding is that when a halyard is being raised and a deck hand is reaching up to grab the line at a high point and letting their weight pull own on the halyard, that is called "jumping the line." When you pull sideways to add the last bit of tension with the help of a person "tailing" (like you did in the video) that is called "sweating."
Came here to say the same thing. Dont sweat the small stuff. I.e. if you "sweat" small lines you will break them.
Their weight, and/or water movement? If the boat is rocking n rolling the two hard points are moving together naturally their weight is only tensioning/locking the shortened line
Thanks for the information
As a youth in the very late 70’s I briefly served as crew aboard an old square rigger used for marine mammal research. Learned the same technique as “swaying” the line. Often a two person practice with the line around a belaying pin, and one person standing ON the rail applying the out-and-down while the other holds tension during out, and takes in the slack as the swayer does the down
Marine here, You are correct, We had the term "Swigging" for helping the sailors with "sweating" which of course means something totally different to a Marine(munitions maintenance) The term came from fighting the Barbery pirates when in sea farring battles the Marines would rig these higher tension lines on a loop pin knot that they could use for "quick ejection" and faster boarding as one of these lines on a large enough ship at full sail can launch several men 50-100 yards. it's combined words rigging and swinging into "Swigging"
If I set up a 5:1 pulley system, in order to lift 100lbs, I have to pull with _more_ than 20lbs of force. Once the load is at the desired height, I can't let go, nor do I have to apply 100lbs of force to keep the load raised. I _do_ have to apply exactly 20 lbs of force (including any friction)
You will be able to hold your 100lbs with less than 20lbs force if there is friction in the system.
AKA you are using the mechanical advantage to over come the high amount of friction. Which in turn allows the system to lock in place
Excluding friction when holding(hence if you wrap it around something you don't need the same force to hold
Technically you would need a little less than 20 lbs to hold it
@@kenmercer2721 Yes, but then it will take more then 20 lbs. to raise 100 lbs. if there is friction.
This is really similar to some 3rd year engineering dynamics final exam questions. Especially the question of "why does the system's advantage change inversely proportional to the systems ability to hold or progress capture when the coefficient of friction is the independent variable?" The coefficient of static friction between the rope and the biner is always higher than the coefficient of kinetic friction after the rope has started to slide. As far as the system is built the slack tail of the rope is not in the system under static conditions, as the tension at the anchor does not exceed the total sum of friction. Although the friction from the final carabiner after the piston dyno is included, but less influential than the biners that have a 180 degree contact with the rope. The higher the coefficient of static friction between the biner and the rope, the more tension it will hold before slipping. Then when adding force normal to the pulley system you are doing 2 things. The first is wrapping more rope around more of the carabiner thus increasing the surface area that friction is acting on. The second is that you are adding potential energy into the rope's elasticity, and getting closer to the impending slip. When you relax the system while pulling the slack through, you are using the stored potential energy in the elasticity of the rope and the lower coefficient of kinetic friction, which is why it works like a progress capture.
So here's the thing; mechanical advantage is still relevant to this system even with the friction involved; in fact, especially with the friction involved. Without mechanical advantage you wouldn't be able to put any serious tension into the system just pulling by hand. The mechanical advantage doesn't disappear jus because there is also a friction force that masks it, and is necessary in order to enable a human to be able to tighten the system up adequately.
Useful video in all practical terms, but I felt like the theory needed a litle clarification.
The friction in the pulley system acts like a tensionless hitch, though probably not as strong
Put it this way: While the mechanical advantage might negate the three to one, it essentially is giving you a frictionless 1:1. if it didn't have the mechanical advantage, you would essentially be fighting against the friction in order to create tension. Instead the MA offsets the friction, allowing the system to appear frictionless, even though the friction is essential to the operation and the 'locking'.
TL;DR: the friction cancels out the mechanical advantage, but without the mechanical advantage, it would be even more work
There is a difference between static friction, that must be overcome to start something moving, and kinetic friction, the force required to keep it moving. Although the kinetic friction seen by the rope sliding over the carabiners is greater than if they were replaced by pulleys, it is not so great as to completely overcome the mechanical advantage, so the hitch does amplify the force you are able to exert. When movement stops, the static friction is great enough to capture the progress. The vector pull aids in adjustment of the hitch because it helps to overcome the static friction.
Well said, and beat m too it.
Truckers tend to pull back through the rope loop rather than carabiners (before the advent of ratchet straps), thus the friction forces were much higher. The static friction also was much higher.
The carabiner hooked through the bite at 1:18 acts like a movable pulley. Mechanical advantage x 2.
So I might be wrong here but, I feel like this dives into semantics really quickly. It's ideal mechanical advantage would still be 3:1 because ideal mechanical advantage is theoretical in a system with no friction, basically the setup with pulleys. The flip side of that is the actual mechanical advantage which is, as the name implies, an actual number that takes into account friction and real world issues. The system with those carabiners and the rope used creates enough friction to offset the theoretical advantage. So basically it's either a 3:1 or a 1:1 depending on which type of mechanical advantage you want to use. Changing variables that would change the friction would still change the AMA, not the IMA though.
I found it very frustrating that they ignored this point
It's the same problem as the trucker's hitch, but worse. Theoretically 3:1, but with so much friction from not using pulleys that you gain almost nothing.
The trucker's hitch gives you 1.6:1 with pure rope or 2:1 with carabiners, but you don't have any progress capture. The voodoo is 1:1 with carabiners, but gives you progress capture due to the capstan effect.
Agreed, if I had a conventional block and tackle at X:1 with rusty pulleys I wouldn't be describing that system as 1:1 "friction". I'd just acknowledge it as an inefficient X:1
Sailor here. Our traveling 420 team used this trick all the time to tie up halyards on masts before strapping the masts to a trailer and hitting the highway. The masthead block and the bail ring were the “anchors” and we used some clever bowlines for everything else. No carabiners necessary.
Yeah he is wrong. Its an inefficient 3:1. Just because it has so much friction that it is effectivly a 1:1 doesn't change the definition mechanical advantage. Nothing is a true 3:1 at most will be a 2.99999999:1 .
Someone saying something is a 3:1 and you saying "no it's a 2.99999999999:1" is pedantic. Especially in a scenario like this were a 10 alpha accuracy is irrelevant.
@@aydinsha thats my point, a 3:1 system doesnt mean it has an actual advantage of 3:1. You call a system a 3:1 because thats the theoretical advantage of a frictionless system.
@@aydinsha Nothing makes an internet comment more factual than it being pedantic. LOL
Very similar to the Trucker's Hitch and the Versatackle, just with carabiners instead of fixed loop knots.
It's called "sweating" a line. You're speaking Swedish.
You count the supporting ropes. If there are 3 ropes in the center vs one on either end, it is a 3 to 1 mechanical advantage LESS the friction of the turns. If you were using well lubed pulleys or blocks, snatch blocks, etc, is is about 5% loss per turn. Slippery beeners maybe higher. I have been using a truckers hitch, utilizing 4 hole boat cleats (functionally similar friction to beeners) for more than 50 years. As you are noting,, I call it a magic knot, you call it voodoo,, because it can be tied in the middle of a rope, and when released it disappears, nothing to untie. With 4 hole cleats I secure the end with a simple cleat hitch,, every sailor, on every sail trim uses. Functional equal to the clove hitch, but open, you don't have to untie anything. I did note the 'perfection loop' at the bitter end. Well done !
I learned this knot arrangement for securing anything, using non binding knots to fully secure ocean bound materials.
Also, it was very helpful in my rigging work on stages.
Sans the ‘biners. I added loops to the line to be able to created the resistance or opposite side of each pulling point.
These days I primarily rely on it for cargo transport atop my vehicle when transporting sheet goods and similar items for my work.
The same high quality lines (rope) I bought in the 90s is still serving me as though they were brand new. Properly stored a good high tensile material can last indefinitely. I wouldn’t rely on climbers lines, since they have a much greater life and death concern.
I used this exact system to set pipes exactly in place because this setup works wonders in its adjustability.
Hysteresis is what holds the tension.
You can put pulleys in some of the turns and it will still work, gonna play with it tonight.
I used to have an illustration I did from playing with the VooDoo of where pulley(s) worked before "failure". Will remake it to share or hopefully dig it up.
This reminded me of something a professor once said about worm gears (worm gears generally have a lot of friction). If a worm gear cannot be back-driven (the majority of worm gears can't be back-driven), then it is less than 50% efficient. Without going through the math, I suspect the same is true of this rope arrangement. Without the pulleys it is less than 50% efficient, so it holds. With the pulleys it is more than 50% efficient, so it doesn't hold the load.
You don't even need carabiners. You can do the whole system with just knots too... Though it is pretty hard on your rope (first carabiner replaced by an alpine butterfly, second carabiner you just wrap around the object instead, third carabiner is just a figure 8 or a bowline.
Sweating is in fact the correct term for vector loading in sailing parlance. Fascinating system for sure!
Correct, which is where we get the term, don't sweat the small stuff from. Because if you sweat the small stuff (thin ropes) you end up breaking them. I.e. don't worry about the little things or you'll end up causing more grief.
@@peterseed5586 that’s a cool tidbit of idiomatic history! Wild how much of our language comes from the days of wooden ships sailed by iron men
This explanation brought to you by C.A.N.O.E.
To create more mechanical advantage, when initially setting up, bring the rope next to the first carabiner, wrap around the bottom and through it then continue to the bottom anchor carabiner then mount the final carabiner. When you pull the rope through and hook the final carabiner, also hook it through the extra loop on the first carabiner. By adding the additional loop you have essentially turned two pullies into 4 like a block n tackle kit.
This is the coolest video I've seen from yall! Awesome stuff!
I've never been climbing before, but as a numbers nerd, this is a amazing channel.
well what are you waiting for!
you could use mechanical advantage to apply more tension on the voodoo hitch but thats about it.
Great video! The voodoo hitch is awesome- speaking of friction, one way to use less carabiners and increase holding power is to use a directional figure 8 and then pass a bight of the working end through the loop of the directional 8, and then just use one carabiner to attach the end of rope to the bight after you have gone around your anchor. The method of tensioning that involves pulling the long strand of the set toward the anchor, and the one moving away from your anchor at the same time takes away the friction when tensioning but holds it in place better. Really cool testing you all did and was great to visualize!
I prefer a butterfly, since it won't lock up like the directional 8. You can actually just use a bowline in place of the second carabiner too. The knot actually doesn't need carabiners at all, though it's pretty hard on your rope without them.
Super interesting to see! Especially since I like to use a similar system (variation of the poldo tackle) for Spacenets. Thanks man!
The carbines are acting as pulleys.
The left carbine is pulled to the left by the force of itself times 2 since it's coupled to itself via a 2 pulley system.
The friction stops the built up tension between the pulleys from releasing.
1:39 No, mechanical advantage doesn't need to move, it just has to exist.
8:34 no, friction doesn't stop mechanical advantage.
This system is reliant on friction AND mechanical advantage.
The left carbine has force X on it's left side, which is looped around the system and coming back into the right side of the left carbine, adding force X, then going back to the right side again, adding force X.
Left side F=X
Right side F=X+X
You need to measure the left side of the left carbine vs the right side of the left carbine with it's 2 inputs measured respectively.
The whole outer system is "inert" since all forces cancel out in total.
I meannn.. I could've told you that? :P It creates friction in almost the same was an an ATC does, with the two sharp bends in the rope. We practice this all the time in whitewater, as it's super useful in a lot of situations. It's great using it like you showed, as a progress capture when vector pulling. This works well in SO many situations! :) It was so cool to see it pop up on your channel!
Swigging! What a cool thing to learn! I will definitely be using that in the future. Thank you so much for sharing all this voodoo knowledge!
I have been swigging this while time and never knew it. Totally agree here.
As another commenter said, it's called sweating, not swigging.
@aspuzling I believe swigging is the correct term.
Unless the old army manual I have is wrong.
@@bryanteaston7264 you are right. I couldn't find any references to "swigging" when I looked earlier but there is a reference on eOceanic which says both terms are used.
@@bryanteaston7264 In sailing.. it's called sweating the lines.. I doubt your army book is talking about sail boats. ;)
My buddy used to call that phenomenon the three crunch rule.. anytime you can get three wraps on anything you can hold it with one hand no matter what the weight on the other end
i use a version off this hitch a lot for tentioning tentlines, where the origional tentioner is missing. Instead off the first carabiner you use a buterflyknot and where the tree would be is your tentpeg, and instead of ending it with a third karabiner you pull it trough the butterfly, pull it tight and ty it off with a slipping halfhitch around itself. its very easy to pull tight and to undo and doesnt require any aditional tools or rope. in my opinion that is where it realy shines, you still have the 3-1 or a 2-1 mechanical advantage without the worry of it losing strength or tention.
This mesmerizing setup is great for making system that is adjustable in length, not adding mechanical advantage. It works using because the two purchase systems balance each other. A 2:1 and a 1:2. They can only be adjusted by manipulating the strands within the system, not outside on the ends.
This system is commonly used on sailing dinghies with trapeze wires as a gross height adjustment. This would be all dyneema and spliced loops, letting the line set into position and maintain the setting, even when the whole system is flopping around on the leeward side. The fine adjustment is done with either a 2:1 or 3:1 as required to balance the boat.
Thanks for confirming history...(aka "Old Guy Here)...I was taught (and have used this for 5 decades now) this is a "tension hitch" and has zero mechanical advantage...What a great channel!!!
“vector pull” is a useless term and whoever coined it doesn't sound as smart as they think they do. Applying a force in a given direction is a vector, but calling it a vector in no way suggests the direction the force is applied. “Apply perpendicular tension” would sound similarly educated but would actually mean what it says.
"OHH YEAH"
I definitely stopped paying attention when he said, "vector pull. Also when he didn't know how to use the configuration of ropes and pulleys to determine mechanical advantage.
Agreed
Mechanical advantage is actually why this system works in the first place. The principle of mechanical advantage here is that by doubling the line from you working end to your top anchor point you reduce the force required to move (or hold tension ) in the system. This allows for the friction on the rope where it passes through the biner to be high enough to hold the system in tention. Without mechanical advantage however, the friction would not be sufficient because the required force to keep the system static would be doubled.
Very nice video!
Good example of the difference between theoretical and real world mechanical advantage. I think it's pretty easy to see the theoretical MA here: you need to pull three metric feet of rope through the system in order to move the load one metric foot. That proves that it's a 3: one theoretical.
The bigger picture here is not necessarily nerding out on whether you get MA or not, but sharing with a larger audience, the beauty and mystery of the voodoo hitch.
It's earned that name for a reason! (I've heard some people call it the WTF hitch!)
1:55 During tensioning you use your hand force to move the rope and 2 bends get essentially removed from the holding equation. During holding there are 2 more bends that hold the rope and they both have their separate force that helps to hold the rope.
If the rope were more slippy it may not hold at all.
This is because the maximum holding force is approximately linear to the force on the rope.
There is some friction coefficient that is above the threshold for it to hold.
If you increase the overall force it may slip because the friction may become non-linear.
If pulled like in 2:28 without pulling sideways then the mechanical advantage (minus friction) is 2 because your hands move twice the way (in relation to each other) than the way the overall endpoints would move towards each other if they weren't fixed.
Mechanical advantage occurs when force multiplication takes place. As soon as you reduce the input force to 0, the multiplication done by any system will result in zero output force. The friction is what maintains a force to multiply.
Motion is only required if analyzing the work being done (no motion, no work).
I suspect mechanical advantage is all about the reference points. Where is your work being put into the system and what resultant motion are you observing. Certainly a complex system. He talked about measuring how much you pull vs how much the system tensions up in terms of distance traveled but he never measured it. That seems like it would be the true indicator of what MA you have referencing two points in the system. When you use two hands it seems it would get even more complex. It's a fun problem. It doesn't seem like they fully nailed it though, to me anyways. Awesome video. I can't see myself using this over other systems though for a tension line, even if just temporary. Truckers hitch seems like it would solve it fine. Small MA with some progress capture works.
well I took the plunge and got my first set of cams from you guys. hope to break them in while camping for the eclipse. thanks for all the vids and info
Originally a french caving technique, they called it a Passabloc. Predominantly used to tension a tyrolean traverse.
I believe The distance traveled is a better indicator because the friction throws off the calculation using poundage. Only if the carabiners were friction free shieves could you use load accurately.
Same principle as the "Trucker's Hitch" but with extra hardware involved.
Point is if you tried to tension something in a more simplistic way you would have mechanical disadvantage. Here you have mechanical advantage over other ways to tensions. "Up to 1 to1"
I use a similar system with just paracord and 2 perfection loops. Same principal, totally not MA!
My guess on outcome using caribiners is that the hitch provides a slight amount of mechanical advantage which enables it to be taut. And just enough friction to hold it there.
'I don't understand how this holds'
The reason is simple. Took a while to work it through, but again it's simple once you see it.
Fold the rope around the narrow end point, and then load the rope. The strands within the rope on either side of the fold back point quickly start deforming and locking in place on both sides due to the rope's internal friction between the strands.
You quickly start requiring very high forces to make this deformed rope part slide around that end point. You have to deform the rope strands even more to make them go around the end point while under load., and the force required will get higher than you're thinking very quickly.
That's also part of why a larger end point for the rope to go around won't work well for this. There's a lot less deformation that would lock it in place with a larger radius. The larger radius acts like an inclined plane to help the rope go around the end more easily, even under load. You need the tight fold back to have a lot of deformation to both sides and easily lock in place.
That's why it's easier to grab the other side of the line and pull both ways to change the tightness. You're unloading it somewhat and jumping that deformed area of the rope around the end point in order to get it into a new position in the rope more easily. Then it deforms and locks in at the new position once you get it set.
That's also why even though this almost completely physically locks up and nearly holds itself, you can't quite just let go of the end of the rope completely. Even with high internal friction and basically physically locked in place, it could still start slipping past itself and loosen up if there were no force at all on the end. But once locked, it could take next to nothing to hold it in place. Of course vibration, bouncing, etc could easily cause it to loosen up and need more end force to hold it in place.
You can easily heat a rope by forcing it through a tight corner due to its own internal friction. And the narrow fold back is like two tight corners close together. You have way more friction than it seems holding it in place at the fold back points, and most of it is inside the rope from the internal displacement and physically deforming around the end point.
It's a two to one, 2:1 mechanical advantage system. I've never heard of a 'voodoo hitch' before but at [1:47] right between the two carbineers shown you have one, two, three lengths of line. This is the only point of the system that is significant. If those carbines were blocks [pulleys for non-sailors] what you actually have here is a two block set up with one fixed pulley, one moving pulley, one fixed end and one end you are pulling one. Three lengths of line: one, two, three minus one equals a mechanical advantage of 2:1. All you have to do is count the number of strands between the blocks and subtract one to achieve the [ideal] mechanical advantage.
You could have had two or three carbineers at either position and all you would have to do is count the number of strands going back and forth between the opposing groups of carbineers and you could count the mechanical advantage of the system. It's about that simple.
People now use carbineers like most people used to use pulleys, and they can no longer visualize what they are doing. They actually used to teach this in high school physics.
Look here for the essentially similar system: czcams.com/video/WuM4KaYndcY/video.html
At a little before 6 minutes I’m wondering how much friction affects it and what if you used pulleys and less than a minute later you went there…. Love it!
This is like half of a Poldo tackle, with carabiners to keep rope to rope friction down. Cool.
Have seen this same arrangement used to produce this result with just running hitches and no hardware.
Use something kinda similar because I can never remember how to tie a truckers hitch. It’s mostly about the force on the “tensioning loop” being equal on both sides
This hitch is pretty genius.
The reason friction doesn't remove all of the mechanical advantage in this system, despite being strong enough to hold the load, is that the action of tightening the lines releases the pressure around the bends that causes the friction. When you pull those lines, you are pushing them towards the carabiners, and as soon as you do that the pressure drops to practically nil and the rope slides easily. The moment the load returns and pulls on those lines, the pressure returns and the friction is enough to resist that load.
So in fact this system is getting the best of both worlds. You get the mechanical advantage when you want to tighten it, but then it can't slide backwards on its own. When you add a bit of force back in the other direction with your hands, that's enough to overcome that friction and allow the line to release.
I would be very interested to see what happens if you attach those load cells to the adjustment lines and tighten it through those load cells, then compare the force being applied through those ropes to the force sustained at the ends. I bet you'll find the numbers are indeed very different. When you leave it to its own devices, the friction comes back into play and obscures what's happening when you're tightening it.
Without looking in detail at the loops,I would assume the locking is due to a ratchet effect in the loop-straight tension causes it to pinch the line, but adding some side force releases the pinching. Think how the lift cord in Venetian blinds works.
Super interesting, thanks.
it is a beautiful example of the capstan equation
Swigging is a fast pull on the line. Lines and ropes stretch, it's hard to get a line tight by pulling. Watch the documentary on the last of the tall ships. You'll see a small group of boys on a halyard swigging against the bight. Incidentally the Swedish word is slurk. Swig is English and has been used since circa 1200.
This is how a snatch block works, or a block and tackle. I also think you are measuring from the wrong end? The force between the puller and the static anchor would be the same, but the line going to what’s pulled would be doubled. The mechanical advantage is applied at the pulled portion. It basically allows you to share the pulling force between multiple static points and the puller, which is why the pulled force increases exponentially with each static anchor (as with a block and tackle)
Yeah this is a less-than-one to one. The energy going into it is stored as friction. And that friction captures the increase in length, which causes some amount of resulting tension across the system.
it's the 2-3-2 swap of number of strands, and the middle one has an opposite direction, so you MUST have a reduction in thread tension as you go around each 'pully' and one of them will have the most friction drop of tension. In the low friction pulley test there is not enough friction to allow the apparent inequality (sequence of tension changes at the 'pulley' points) to be maintained.
I've certainly had it demonstrated as a (loaded) canoe recovery technique, but it's real hard to sort out how to set it up! It's does feel odd when you have a 'free' line system that holds tension.
Great content. It's called sweating a line by sailors these days FYI. Still used on deck all the time.
Because you have both ends of the rope tied off you have a closed system. As you tension it you're applying energy from outside the system so that must stay in the system as the tension until more energy is brought in from outside the system to release it.
whenever you have the zigzagging rope like that it's a pretty obvious sign of mechanical advantage. same idea as pully systems.
3 passes of rope, you have to pull 3x the distance, so it's 3:1
Don't forget that you're measuring external forces. We know that core forces are not the same, from the proclivity of breakage 1,5 diameters from the point a flexible rope becomes rigid entering a know, it's the point where the forces reflecting off the rigidity bouncing off the external wall refocus. Force cannot disappear, nor can it be shed into air or liquid ither than as heat. When you replaced the hitches with pulleys, you removed the reflection.
It sounds like this arrangement takes advantage of the interaction point between friction defined & movement defined systems; they've identified a usable area where that jerking then pulling motion can control the transition between the two modes.
It feels like learning about supercritical fluids; fluids that are Both liquid & gas, because temperature &/or pressure are manipulated.
I’m begging you guys to reach out whenever you want an engineer to double check some of the climbing math that’s happening when you talk about things like “mechanical advantage”
Friction can be your best friend or worst nightmare with tying knots and rigging.
Suppose that carabiner 2 is attached to the ceiling and carabiner 1 is attached (via the tail of the line) to a weight. At one extreme, carabiner 3 is touching carabiner 1 and the distance from 1 to 2 is 1/2 l where l is the length of the rope (ignoring the tail that connects 1 to the weight). At the other extreme, carabiner 3 touches carabiner 2 and the distance from 1 to 2 is 1/3 l. Consider a 6 meter line. Initially the distance from 1 to 2 is 3m. After 3 moves up these 3m the distance from 1 to 2 is 2m. For every 3 cm you move 2 up, the weigh moves up 1 cm. So there is 3 to 1 mechanical advantage, which allows you to make the line taut if you are connecting two fixed points, But there are also 3 places where there is static friction, which allows enough stiction for the set up to be stable under load. In fact the more taut the line the higher the static friction. (Roughly linearly.) I’m no climber, but it seems to me it would be stupid to suspend a person using this unless the line from carabiner 3 were lead back toward carabiner 2 and tied off at carabiner 2 or to something equally immovable.
The line bends over a carabiner at three places. Presumably it will slip at one of these when the ratio of the tension on the two segments reaches some critical number. A little slippage at one bend tends not only to even up the forces there, but also at the adjacent bend(s). So the whole system will tend to a state where all the ratios are under the critical angle if such a state exists. (I’m ignoring the difference between static and dynamic friction.) In this case, all the ratios are equal when they are at all at about 1 to 1.3. So as long you can pull one end of a bend at 1kN and the other at (a little more than) 1.3kN without the line slipping, the hitch should hold. I wouldn’t stake my life on it though; I would tie carabiner 3 to carabiner 2.
Friction is handy sometimes.
I find these types of experiments very interesting.
I am curious what the actual mechanical advantage is with a vector pull force in comparison to anchor points. & does it change dramatically when the length of the anchors are closer/further away from each other.
You can actually calculate exactly how much mechanical advantage is from “vectoring” or “swigging” a rope. If you know how much force you are applying and the angle of the rope it is vectored to.
The length of rope will make a difference in the amount of mechanical advantage that can be applied since the stretch of the rope will account for lost captured force- but also might aid in helping create momentum to vector farther. That would be a cool experiment.
Anyways, The force applied from a vector in the rope is only going to create mechanical advantage until the rope makes a 120 degree angle. That is the point where the force applied to vector the rope is equal to the force on each side/anchor. And before you deflect the rope at all when the angle is 0 degrees, you have hypothetically “infinite” mechanical advantage (as soon as you touch the rope though you deflect it to a different angle, changing the mechanical advantage)
If you take the angle of the rope at the greatest deflection, and divide by 2, and then take the force applied to the rope, divide that by 2. Divide the force /2, by the cosine of the angle/2 that gives you your force on one anchor. Assuming deflection near the middle of the rope the force would be the same on both sides. For example to show why 120 degrees is the point where all forces are the same you can do the math by taking 120degrees/2, then take a force of say 50lb/ft/2. Now we have 60degrees and 25lb/ft. The cosine of 60 is 0.5, so 25/0.5 is 50. So 50ft/lbs is your force on all 3, directions of pull. That’s a method used to determine forces on high lines which has the same physics to determine the force as this scenario
Should try it with ratchets - mechanical adv. when pulling, and then trapping in the ratchet mechanism.
I've used a similar system for solo tensioning a slackline (not highline) between trees using 1" tubular nylon webbing. I'm curious if that also has no effective mechanical advantage because of the system's friction.
The advantage is still there, but as there is no movement, it doesn't matter.
It's held together by the static friction, like a frictionless hitch is.
When that is overcome, like someone side loading it, then you have the sliding friction contracting the movement of the slippage, and this is modified by the mechanical advantage. You can probably grab the zig zag of roses, and that would be enough to stop all the slipping.
Excellent video, clear and informative even to a non climber like me.
The mechanical advantage is still there, but it is amplifying the holding friction.
Yes! I love the Voodoo!!!
I would say that in an ideal rope with no stretch, there shouldn't be any mechanical advantage.
The easy way to see it is to consider the rope in 2 parts.
The first part of the rope goes from the point is is tied off, through the first carabiner, to the carabiner that has the rope tied to it.
The second part is the continuation of that back through the first carabiner, around the tree (or whatever) and back to the carabiner that has the rope tied to it.
This second part is just a loop, which circles around, so it doesn't change length, so it can't provide mechanical advantage.
The first part is basically just a rope from the carabiner to the tie off point, so it doesn't provide mechanical advantage.
The only mechanical advantage that would come is from the rope stretching.
This allows the loop to shrink slightly as the portion of the rope from the tie off point gets longer.
But this is a very small advantage so it will be close to 1.
Also, mechanical advantage exists in both moving and static systems. In static systems it is force.
It's not mechanical advantage it's simply newton's law. You have two points being lashed in place as one with equal and opposite forces suspending it in place because neither force is stronger than the other but both have added potential energy greater than any outside force(i.e. gravitational)
5:30. I'd say the peak of 3.5 is the advantage but that is with it levering/vetting at 180/ 170° pull
But if still lock it off. It almost looks like a truckers hitch which doesn't lock (no clove hitch, but also essentially generates cutting forces without the carabiners) but no clove hitch even without the carabiner you Def have mechanical advantage
Conclusion early on, I would not trust it for lifting human weight. Proven true weather it's 1.1 or 3.1 advantage
The old Poldo tackle.
If Brent guessed it was going to break anywhere other than in the knot... Guessing he was wrong. #ItBrokeInTheKnot
Mind. Blown!
Maybe i'm understanding this wrong, or rather approach it wrong, but it does have a mechanical advantage, working in the middle to give the system tension but the way the tensioning carabiner is suspended from both sides it cancels each other out? I guess maybe that's also what's the debate here? If you can call it mechanical advantage even though it's wasted on friction and creating an opposing force by suspending the tensioning carabiner from both sides? It's a rare form of mechanical advantage, that's not giving you advantage. :D I'm curious what would happen if you put tiny pulley (Petzl Rollclip maybe?) will it still be unfunctional, or if you put a huge shackle (theoreticly bigger contact patch=more friction but bigger bend radius should slip easier when acting as a pulley?)
Here in germany the DAV recommends a double bowline(without a stopper knot) to tie into your harness as an alternative to the figure eight. Some other ressources say a stopper knot is mandatory when using a double bowline. So what is it? Does it really slip?
Bowlines are a little more likely to loosen or slip - particularly with very new/stiff rope. They can be used, and be safe, but as with anything here, there are considerations. I would tie a stopper knot, but I also have developed a habit of using a Yosemite finish as I know it to capture the tail on a figure 8. Incidentally that finish helps make the knot easier to untie after loading, which is one of the reasons people do use bowlines instead.
Back up everything when reasonable and possible, trust but verify, don't eat yellow snow (unless you're into that)
Two different knots and a translation issue - and an inconsistency in naming knots in different sources possibly so use Ashleys Book of Knots numbers to clearly differentiate.
The DAV approved one is correctly translated as a bowline on a bight(ABoK 1080), not a double bowline(ABoK 1013), the latter is a different knot that seems to need a stopper.
@@iDayrrYou are right. But even then, the english language wikpiedia for bowline on a bight (ABoK 1080) says "However, it is critical to use a strong backup knot with plenty of tail beyond the knot, as the knot may untie during long climbs"
So some people seem to think you need a stopper knot or similar.
Hello Guys...
Love your Videos Ryan. Keep doing them.
I am no scientist, but i think the pulleys mechanical advantage by friction is null because the wheel im the pulleys are moving parts, they spin while the rope moves passing through!!!
Don't know if this is accurate or scientificly possible to check and prove, but it makes sense to me, and that is why i thing the sistem doesn't lock.
Love to know what you guys think and see if it makes sense for you.
Cheers!
It's supposed to be a 3 in 1 but the 3rd carabiner but it's supose to go all the way through or I'll usually have a order wrap to pull a tree down I've even applied the rope jack ti the same system and pulled trees over leaning the opposite way its a very good advantage and helpfull in the tree industry
I've even set up 3 3 in 1s for one live oak it was way easier to pull it over
Also I I'm also playing with dunasorob rigging line the red one
It's rated at like 18000 lbs so I could be wrong but croect me it'll it bothers anyone but will strength is a fun game 😅
could you guys stress test the flytrap knot,
i want to know what it can and cant do but dont have the machinery on hand to do so
Looks to me like it should have a 3:1 mechanical advantage, but a lot of friction.
Also, it seems risky putting your hand inside that loop between the two carabiners. Are you doing this on a live load, or dynamic lines?
its obvious as soon as you made the hitch that it has divided the tension through two or more "blocks" thereby increasing the leverage
Your moving part is the pulley that moves between the other two.
So if you pull your "set" carabiner 10cm back (ingoring that the ropes are slightly elastic) and your load carabiner goes anything less than 10cm back, you have a mechanical advantage.
You're basically making a tautline hitch. That's why it doesn't hold when you use pulleys. But instead of the rope wraps in the tautline, you have carabiners
The third carribeener serves as a pulley and the back loop produces a two to one advantage (or halves the load at carabiner 3) allowing it to hold its position
Epic frigging content!
(02:05) _“I can pull a vector force...“_
_Vector_ force? Every force is (also) a vector; that is saying nothing. (Yes, I know what you mean.)
There is already a knot-related term: _frapping force._
Agree, "perpendicular force" (perpendicular to the rope) would be a much better term.
So as long as the holding friction in the system is more than 1:1, it should not allow the rigging to move on its own. It looks like it's 2:1 because measuring the mechanical advantage of the system without much friction it's 3:1 and with the carribeners or scales approximately 2 of 3 of the mechanical advantage are consumed in friction leaving about 1:1 at the outside load measurements.
That's my understanding of why it holds. It will hold as long as friction in the system is greater than the required input tension
And in this case that required input tension is 1/3 of the outside anchor point tension at the outer terminations of the system
Did you try the simulations swapping out carabiners for pulleys one at a time?
My immediate guess, based on Technical Rescue work, was it’s a 3:1. I still think it is but not certain 😂
Is the second biner almost like a prusik capturing the load?
I can't help but ask, "what about ratcheting pulleys?"
Would still be low friction when adding tension, but the ratchet would preventing it from rolling back. Seems like a best of both worlds kind of deal.
Now I want to see this tested!
I also want to see them test this with just knots (no carabiners). That can be done with an inline 8 or butterfly in place of the first carabiner and a fixed loop or a barrel knot in place of the other (alpine butterfly and bowline are my choices but would love to see different options tested).
Why can't you add pulleys on the anchor side and the carabiner to the other side for friction?
What if you added progress capture to the pulley system though?
I don't understand a damn thing, but I like your funny words mister mechanical advantage man.