Author Topic: Opposed bights locking mechanism.  (Read 6551 times)

xarax

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Opposed bights locking mechanism.
« on: May 20, 2014, 05:32:54 PM »
   With the contemporary hardware and software tools, there is no need to select a limited number of views of the object ( of the knot ) any more : we can rotate it, and see it from any side we wish. ( So, there is no need to decide which should be THE "front" and the "rear" view, which, in the case of the bowline-like loops, was the subject of a long, heated debate some time ago in the Forum... )
   See, in the attached pictures, some views of the most efficient locking mechanism of the Tail End we have : the opposed bights mechanism. ( The two U-like bights are supposed to be tensioned, of course ). I feel that this simple, structurally, knotting mechanism is not yet understood / appreciated by many knot tyers, so I believe that a somehow simplistic but clear 3D representation of it, like the one presented here, could be of some help.
   
  Notice that the .pdf file is only 24kB, about the size of one small picture - yet one can isolate any element of the mechanism, and show or hide it, from any angle he wishes, he can change its colour, transparency, etc.
   This object was designed with the help of a CAD program - however, we can do the same thing, with pictures of the object taken from many different sides, and merged in one 3D virtual object, which we can then rotate, zoom, etc, in the same way.
« Last Edit: May 20, 2014, 08:04:37 PM by xarax »
This is not a knot.

xarax

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Re: Opposed bights locking mechanism.
« Reply #1 on: May 20, 2014, 05:34:08 PM »
 2. ( Click at the last attached file, to open / save the .pdf file. By opening the toggle mode tree and un-checking the "Geometry", you can hide the annoying geometrical lines, change the colours, lights, etc. )
« Last Edit: May 20, 2014, 05:38:08 PM by xarax »
This is not a knot.

Ruby

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Re: Opposed bights locking mechanism.
« Reply #2 on: May 24, 2014, 01:20:38 AM »

    ...
  Notice that the .pdf file is only 24kB, about the size of one small picture - yet one can isolate any element of the mechanism, and show or hide it, from any angle he wishes, he can change its colour, transparency, etc.
...

downloaded. but it's blank. nothing can be seen.


« Last Edit: May 24, 2014, 02:17:40 AM by Ruby »

xarax

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Re: Opposed bights locking mechanism.
« Reply #3 on: May 24, 2014, 01:39:06 AM »
I downloaded. but it's blank. nothing can be seen.

   Check it again. Nothing is wrong with the file, which can be "opened" at once, or be "saved as" and opened later, with Adobe Reader. Perhaps the problem is with your browser (?). Try to "open", or "save as" and open later, using a different browser.
   See the attached picture, of a print-screen image, just after you reveal the toggle model tree, and expand it.
   If you wish to start from a series of pictures and not from a 3D CAD model, use the 123D Catch of Autodesk.
   http://www.123dapp.com/catch
« Last Edit: May 24, 2014, 01:47:52 AM by xarax »
This is not a knot.

Ruby

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Re: Opposed bights locking mechanism.
« Reply #4 on: May 24, 2014, 02:36:44 AM »
OK, I see.

I opened it with a software named "Simple PDF reader" and it's blank.

Now I installed the full Adobe PDF Reader and it's OK now.

good to know that PDF support 3D. thank you

DerekSmith

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Re: Opposed bights locking mechanism.
« Reply #5 on: June 01, 2014, 10:15:58 AM »
snip...
 so I believe that a somehow simplistic but clear 3D representation of it, like the one presented here, could be of some help.
snip...

The only trouble with 'simplistic' representations is that they are wrong.  Our knots are complex analogue force vector machines, not simplistic representations.

For example, if the two bight loops are loaded and are nipping the red line, of which presumably one side is loaded, then the two bights will arrange themselves into a more 90 degree alignment and the red line will be distorted into a 'S' shape.

Well done for creating those images, but they are only imaginary representations and do not reflect the reality of the machines you claim them to represent.  Sorry to be critical, even though I cannot do better or even as well myself, but we must not confuse pretty symmetrical pictures with the reality of our force vector machines.


Derek
« Last Edit: June 01, 2014, 03:33:57 PM by DerekSmith »

DerekSmith

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Re: Opposed bights locking mechanism.
« Reply #6 on: June 01, 2014, 12:10:01 PM »
I am feeling a little bad about criticising Xarax's reference to 'simplistic', especially as this could have been a language artefact, because in our efforts to understand knot function, we are indeed forced to 'simplify' the working knot in order to have the remotest chance of representing it.  But in doing this we have to remember the parameters we had to ignore or standardise in order to create our model.  Initially, that list is going to be quite substantial.

I have wrestled with this problem for some years now.  Starting with the very (and here I will use Xarax's term) 'simplistic', and almost useless 'Overs Index', then moving on to the sketching software that Dave Root has matured into the very usable drawing utility 'KnotMaker'.  This lovely utility now feels as though it is only a spit away from 3D shading and even 3D viewing, but anyone who understands programming will know that it is a long cry from two and a half D to full 3D.

Partway through the development of KnotMaker, I started to realise the limitations of 2D and became aware of the reality that knots are 3D analogue force vector machines.  To represent the force vectors within a knot is a serious challenge.  Even to represent the force vectors inside a piece of laid or braided rope is a challenge that probably demands the combined intellect of a dedicated team.

So, we simplify.  Consider a rope or cord to be a section of mono-filament with a linear 3D force vector running along its length, surrounded by a cloud of radial force vectors through its cross section.  Now add in frictional and torsional vectors and animate the application of end loading on the cord.  Finally add the ability to 'fly into' the loaded knot in order to inspect the distribution of forces, and we will have a first order approximation of a working knot (subject to the list of simplification we had to make in order to achieve this model).

Any takers?

Derek - with apologies to Constant Xarax

xarax

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Re: Opposed bights locking mechanism.
« Reply #7 on: June 01, 2014, 02:37:56 PM »
The only trouble with 'simplistic' representations is that they are wrong. 

  True. However, there are representations that are less wrong that others, and representations that are not even wrong...  :)
I wonder in which of those two categories the one shown in the attached picture belongs... We can see that the author / knot tyer, has not understood clearly the essential elements of the whole thing, which needs one, only, passage of the Tail End in between the opposed bights, in order to "lock". ( See the second attached picture )

if the two bight loops are loaded and are nipping the red line, of which presumably one side is loaded, then the two bights will arrange themselves into a mote 90 degree alignment and the red line will be distorted into a 'S' shape.

  Correct. I had done this, but the result was a not-compact nub, which looked even more artificial... I decided that it was better to show the penetrating line as a straight line, and the two opposed bights in contact to each other. One other inaccuracy is that the segments of the two U are shown as following elliptic tori, tangent to two planes, while they should have been shown as following helical paths.

we must not confuse pretty symmetrical pictures with the reality of our force vector machines.

   That argument is wrong ! In a state of equilibrium, the two legs of the two opposed bights tend to become equally loaded, so, provided that the Tail End remains, more or less, a straight line, the mechanism IS symmetrical as a force vector machine, too. It would had worked in exactly the same way, even if we were not forced to ignore the minor asymmetries of the loads on the four legs, due to the capstan effects.
   Noope, the symmetry of the picture is the very last thing that is simplistic in this representation !  :) 
« Last Edit: June 01, 2014, 03:13:57 PM by xarax »
This is not a knot.

DerekSmith

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Re: Opposed bights locking mechanism.
« Reply #8 on: June 01, 2014, 03:49:05 PM »
I won't labour this point any further, as I feel I have already been over strident in my comments.

I would agree that some representations are correct.



This schematic for example is showing how to lace up the construction, it is not attempting to describe how the knot functions under load.  It is a tying diagram, not a description of function.

xarax

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Re: Opposed bights locking mechanism.
« Reply #9 on: June 01, 2014, 04:03:15 PM »
   The idea is to "implant" the essential elements of this mechanism into the knot tyer s brain, leaving aside the minor details. Of course, a "representation", any "representation", is always wrong, be it "simplistic" or not... A detailed, complex representation is often more wrong, because it blurs the amounts of the contributions of each of the many individual "elements" into one incomprehensible "whole".
   There are applications of this mechanism where the visual "picture" is completely different, yet the mental "picture" remains the same : The locking mechanism of the Locked Single Cow hitch, discussed in the other thread, is nothing but an opposed bights mechanism, but if one has not a simple and clear picture of how it works in his mind, he will fail to recognize it - because the two legs of the one opposed bight form a 90 degrees angle, so they are not parallel. They may be part of an overhand knot or any other "closed" knot, so the "U" shape they form may look more like an "L" shape - but the mechanism remains the same. Read how I had described it, when I was trying to simplify the original TackleClamp hitch. I was lucky, but, helped by this simple and clear picture, my mind was prepared for it... :)     
   
The " lock" remains the same, the efficient squeeze of the tail in between two opposing U s - but now the one U is a part of an overhand knot tied along the tail segment
The same old story : a standing end emerging out of a "lock" made of two opposing bights - where in place of the second bight we use a segment of an overhand knot.

P.S.
  It is a tying diagram, not a description of function.

  True, but the reader may be left with the ( false) impression the locking mechanism is due to the many wraps, and the friction in between the segments of the many penetrating U s. I have sensed that there was no simple and clear representation of the function of the opposed bights mechanism, ( utilized in the Trucker s or the Versatackle hitches, for example ), and that is why I had attempted the one shown in this thread... 
« Last Edit: June 01, 2014, 04:15:13 PM by xarax »
This is not a knot.

xarax

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Re: Opposed bights locking mechanism.
« Reply #10 on: October 15, 2014, 06:17:53 PM »
   A CAD - made image you can rotate and look at the virtual object from different sides, like the one presented in this thread, is fine, but pictures of the real thing are even more fine - and the real thing is the super-duper finest of them all !  :)
   I had realized that there are 3 1/2 years since I had posted my first picture of the opposed bights locking mechanism (1), applied in the case of a Trucker s hitch. So, have a look at 4 more recent pictures, taken from different sides. They are not as clear as I had wished  ( to take really clear pictures of knots, one has to use even a cheap 6 x 6 medium format film camera, with a not-zoom, prime pancake lens, and then digitize the picture using even a cheap scanner !  :) ), but they are better than the ones shown previously and elsewhere...
   I do not know if Ashley himself had understood clearly the idea behind this mechanism shown in ABoK#1524, I am pretty sure that the author of the Versatackle hitch had not ( most probably, like his readers, he was under the ( false ) impression that the efficiency of this mechanism was due to the many wraps, and the friction in between the segments of the many interlinked U s ), but now there is no excuse for anybody not to have the abstract picture of it in his / her mind - and use it when it is required. It is the best mechanism which "captures the progress" of the pre-tensioning of an end of a knot we have. ( I had used it in the TackleClamp hitch, for example )
   The beauty of this mechanism lies not only in the way it "locks", but also in the way it "unlocks', and releases the Tail End, at an instant. This can be understood only in the case of the "pure", "elementary" configuration, with only two opposed bights and the Tail End immobilized in between them, as shown in this thread. One has only to "untuck" the Tail End through the bight of its link, and pull it slightly "sideways", without pulling it lengthwise at all, so its L-shaped curvilinear part / "handle" which was previously located in between the tips of the two bights, now gets out of their squeezing = gripping touch : the hitch is released at a glance.

1. http://igkt.net/sm/index.php?topic=1870.msg17364#msg17364
« Last Edit: April 13, 2015, 09:49:56 PM by xarax »
This is not a knot.