The capstan equation is good to understand holding force on one side of the turn compared to another(hysteresis also in play). To add the elastic nature of dynamic climbing rope messes it all up as well as the equation is reliant on non elastic material as stated in the article linked. Unfortunately I don't think it useful for determining anything in this context, but excellent for nerding out on. It is absolutely correct 2 90's put more friction. How much? That's what matters. If it is tested to be negligible, then that would make the results hold water, but at this point, that is unknown and my point of contention. I work in entertainment performer flying, and we will use carabiners in place of pulleys sometimes because of the added friction in counterweight systems. It is quite noticeable when pulling a rope between 2 pulleys, and 2 carabiners in a configuration (even with 0 load) that runs just like what HIE has set up in that vid. Anecdotal evidence I admit, but based in reality.
To your point #2. Thats an assumption based upon what factors? how may draws, what angle of turn at entry from belayer, what kind of rock, contact patch of rope to rock, how much force is the rope being pressed into the surface, etc etc etc. It not useful for this discussion around the testing method issues I'm bringing up. You're absolutely correct it could add more friction but I just dont see how its useful in this discussion currently. Basically, if hard is easy sussed the friction in the system it would have more give the data some meat IMO.
I may take some time to work the friction out of a 90 degree turn to get some very general numbers to apply! I think it would be good information to have out in the world. I have few flights coming up that will offer some good time to dive into this. Heck, there is probably good info out in the world already around it that I will attempt to google-fu my way to it.
In the end, it would not be hard to create a fall scenario with it running through a single carabiner anyway and could provide a more accurate test.
I saw this and is useful to understand the kind of forces that the gri gri relies on to engage. That video is riff with issues as well, and not for this discussion as this is not a gri gri. Although doing more testing like in that video would be cool to see with the neox for sure.
Preach brother!lol.
I appreciate your input and love the rabbit hole I am now in. How deep does it go!
I'll seeif I can extract the information fro a paper I wrote years ago but yes 2 x90° is vastly different to 1x180°, in fact even the seperation between the 90's makes a substantial difference. The Capstan equation is worthless because in a climbing rope the majority of the " friction" is actually generated in the rope resisting bending (the friction between the individual filaments of the rope actually have to slide past each other for it to conform around the object. I built an exact replica of an ATC but using needle roller bearings to demonstrate this for a lecture I gave once.
Mr Rogers
·
Jun 16, 2024
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Pollock Pines and Bay area CA
· Joined Aug 2010
· Points: 77
I'll seeif I can extract the information fro a paper I wrote years ago but yes 2 x90° is vastly different to 1x180°, in fact even the seperation between the 90's makes a substantial difference. The Capstan equation is worthless because in a climbing rope the majority of the " friction" is actually generated in the rope resisting bending (the friction between the individual filaments of the rope actually have to slide past each other for it to conform around the object. I built an exact replica of an ATC but using needle roller bearings to demonstrate this for a lecture I gave once.
I am not surprised of all the folks on here you would chime in as having had done tests around this exact scenario. Would love to see that paper or an abstract if you find it!
I would like to add, I finally got a chance to use the neox a bunch today. Its dreamy. Huge fan of it and very much see it being an awesome LRS / TRS device.
That clicky sound is so annoying when he lifts the "climber" up, I really can't believe nobody talked about this before (unless I'm blind?). I now hope this doesn't actually become the more popular device haha.
The release version of the Neox actually had the clicking sound "fixed"- the initial prototype all the big names/guides/retailers got sent samples of had a much louder clicking noise.
I'm currently at City of Rocks, haven't got this out on an actual wall yet, but, it's been in quite a few hands on the ground, and, yeah, it's got some " limitations", as does everything.
I do think, as do others, that people who are ATC users will enjoy this....
But.
I also think it will be pretty dangerous in the hands of grigri users with bad habits....but those folks are just accidents waiting to happen anyway.
H.
Well, for one, when you lower someone, as soon as their feet touch down, the wheel lock tends to disengage, and there's suddenly 0 friction.
I am not surprised of all the folks on here you would chime in as having had done tests around this exact scenario. Would love to see that paper or an abstract if you find it!
I would like to add, I finally got a chance to use the neox a bunch today. Its dreamy. Huge fan of it and very much see it being an awesome LRS / TRS device.
As you can see it's the first part of the bend makes the most effect, the difference between 90° and 180° wrap angle of the rope is quite small so depending on the rope etc maybe only a 20% increase. The rope bending resistance is the dominant force of the friction around a karabiner making between 60 and 70%.
The important thing to know is the energy required to bend the rope is lost (it goes away as heat) so when the rope straightens (which does actually require some energy in itself) and then has to bend again there is another energy input required. As you seperate the two bend radii this amount of energy increases (when they are close together the rope doesn't really straighten out properly) and by experimentation we see that for a normal climbing rope around 10mm karabiners this peaks at a seperation of around 7x rope diameter with an increase of roughly 20% (there are people who insist that having two biners at the top when top-roping reduces the friction, they are completely mistaken). This is the reason that taller tube belay devices like the ATC work better than the more modern flat ones.
Setting aside the applicability of the Capstan equation, addressed by others above...
What numbers are you using to come to this conclusion? e^(μ 2ϕ) ≠ 2 e^(μϕ). It's approximately true when the product of the angle ϕ and coefficient of friction μ are small but it's not obvious to me that this is the case here.
I am not surprised of all the folks on here you would chime in as having had done tests around this exact scenario. Would love to see that paper or an abstract if you find it!
I would like to add, I finally got a chance to use the neox a bunch today. Its dreamy. Huge fan of it and very much see it being an awesome LRS / TRS device.
Brent Barghan tried it for LRS and found it to be terrible. Dude took 20 LRS whippers for science. The Neox hit the stopper knot every time. He posted to the LRS FB group.
My first impression of the Neox is that this has been specially made for lead competition.
Like I wonder if the IFSC has a mandate for assisted locking belay devices incoming, and this is for compliance. The pros and wannabe pros who are preferring an ATC belay right now, wanted something different to the Grigri with fast and smooth feeding above all else.
My first impression of the Neox is that this has been specially made for lead competition.
Like I wonder if the IFSC has a mandate for assisted locking belay devices incoming, and this is for compliance. The pros and wannabe pros who are preferring an ATC belay right now, wanted something different to the Grigri with fast and smooth feeding above all else.
When I was letting people try it out at City of Rocks recently, that included a couple who were involved with team competitions, and that was the first thing they said, "bet this would be great for comp climbing,!".
The Neox seems to be a better choice for cold/wet conditions wearing gloves & mittens because less finger dexterity is required. Curious to hear from others about partner multi pitch experience.
I used one for the first time this week. Its pretty neat but sure it felt nessecary. Feeds slack out quicker/easier and feels more like a ATC. Still locks when pulled on quickly like a GriGri but it seemed to take a little more force and not lock as quick (maybe could make falls a little longer). You can top belay with them and my friend said it felt really smooth and easier than an ATC, while also safer. To be honest, I am not sure that I'm sold on it yet. I did not get the feeling it was better than than the GriGri, especially at the price. I did not get to use it long and these were just some quick thoughts.
K Go
·
Jun 23, 2024
·
Seattle, WA
· Joined Oct 2017
· Points: 170
You can top belay with them and my friend said it felt really smooth and easier than an ATC, while also safer.
Safer than an ATC for a top belay is objectively inaccurate. Smoother and more convenient, sure, especially for lowering if needed, but an ATC in guide mode belaying has fewer failure modes and is basically hands-free.
Jared E
·
Jun 23, 2024
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CO-based healthcare traveler
· Joined Nov 2022
· Points: 417
Safer than an ATC for a top belay is objectively inaccurate. Smoother and more convenient, sure, especially for lowering if needed, but an ATC in guide mode belaying has fewer failure modes and is basically hands-free.
Not mention the less readily an abd cams (and neox looks damn near the least) the more the rope will slip through in guide mode
Always makes me cringe when I get up to a belay and my partner is full hands-free on a grigri or similar in "guide mode" configuration lol. The brake strand tends to be perfectly oriented for slipping through without triggering the cam.
I used one for the first time this week. It’s pretty neat but sure it felt nessecary. Feeds slack out quicker/easier and feels more like a ATC. Still locks when pulled on quickly like a GriGri but it seemed to take a little more force and not lock as quick (maybe could make falls a little longer). You can top belay with them and my friend said it felt really smooth and easier than an ATC, while also safer. To be honest, I am not sure that I'm sold on it yet. I did not get the feeling it was better than than the GriGri, especially at the price. I did not get to use it long and these were just some quick thoughts.
Use in ‘top belay/guide mode’ seems like the missing feature. Interesting/cool/not cool that it is getting used that way.
Interesting point made in the video is the Neox needs about 20kgs of weight for the wheel to lock and for the device to act like a GriGri.
Is it possible that Petzl cannot certify guide mode because a child or pack weighing less than 20kgs is light enough that its weight would not lock the wheel in guide mode and the device would not arrest a fall?
Jared E
·
Jun 24, 2024
·
CO-based healthcare traveler
· Joined Nov 2022
· Points: 417
Interesting point made in the video is the Neox needs about 20kgs of weight for the wheel to lock and for the device to act like a GriGri.
Is it possible that Petzl cannot certify guide mode because a child or pack weighing less than 20kgs is light enough that its weight would not lock the wheel in guide mode and the device would not arrest a fall?
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