Physics debate

[randoskier]

Re: Physics

Einstein couldn't ski for shit!

[TallGrass]

A lot of their difference comes from where and how cables are attached. Others have reached same conclusions elsewhere, see citation below. It might have been nothing new to @lowangle al so I do see why this might not have felt relevant. Just old things expressed in an new way.

Consider 22 Designs Axl and Voile Switchback as examples. The reputation for these two bindings are at opposite ends of the activity spectrum, with the Switchback being a ‘neutral’ cable binding and Axl, the free-pivot descendant of the Hammerhead, the epitome of adjustability and the benchmark of comparison for tele power. […] Resistance to heel lift can be determined with a lil’ trigonometry by splitting the vector representing the spring force of the cable into vertical and horizontal components. Analyzed this way it is easy to see why the Switchback is more neutral than an Axl in position 3 (or 2 or 1).

https://earnyourturns.com/34754/diy-2-p ... orce-luke/

Agree (and as posted prior) that some systems are free-pivot (like this frame pivot) and others are not as the boot (sole, last) often becomes part of the equation ala a triangle making it operate differently, same as when you add a spring or damper to a screen door. If a heel-band-binding/cable pivots in the same axis as boot flex, it is effectively* "neutral" (* my gut tells me a flexing leather boot forefoot doesn't have a rock-solid pivot point, so a little give is accorded).

When the axes/axiis of boot flex and cable-pivot are not in line, you'll get a camming effect, similar to the way a heel-clip flips over a cam point.

Comparing the rate of angular increase. For approximately 20° of heel lift, the Switchback cable changes 21°, Axl 25°.


The steeper the angle, the larger the vertical component of force (€”resistance to heel lift)€”
otherwise known as activity. (Angles shown are simple examples, not measured values)

Source: https://earnyourturns.com/34754/diy-2-pin-tele-use-the-force-luke/

Here's a re-work of prior flipped to match the above L-R orientation, with the 2-Pin Pivot noted in orange.


I think everyone would agree that this is a free pivot, and any "tension" in the binding holding the boot is isolated from the pivot in front of the toe.



Ok, folks, now everybody go over to Wikipedia so we can create a page and edit it to perfection!

[lowangle al]

They're some good diagrams there. That's what I'm feelin. So does that settle the debate?

[Stephen]

So does that settle the debate?

I think the only one who can answer that may have left the room.
Otherwise, it doesn’t seem like there was ever much disagreement.

[leon]

I personally agree that this topic has reached the limit of useful discussion. However, perhaps the topic cannot be officially closed until Sir Issac Newton himself posts his preference of binding: NTN vs 75 mm.

[TallGrass]

It’s about the cable. It has always been about the cable. I’ve focused on the NN 3 pin 75mm binding because of two things:

1. That’s what started the discussion, so it makes sense to stick to the to the topic for the purposes of consistency; and

2. How the cable interacts with the NN 3 pin 75 mm binding (which is fixed to the ski and has no moving parts other than the bale).

This topic has always been about the NN 3 pin 75 mm binding. People might not like that because it avoids the issue of how these bindings work differently than some may have thought.

Does anyone see the cable changing length here?


Look at silver end at the front of the cartridge as the heel is clipped in, and again as the boot rotates up and down @ 2:25 and also @ 4:25.


By comparison, you can see extension comparing the silver part at the front of the cartridge in these two images.



Images from: https://earnyourturns.com/1313/review-day-2-on-tts-beta-binding/


Disclaimer: My cables for my NN 75mm 3-Pin boots have a different geometry, where the cable wraps rather than rotates near the ball of the foot.

[Stephen]

Yes, the cable mechanism gets longer as the spring in the cartridge is compressed.

Where do we go from here?

[DG99]

This particular case seems like it might not have any downward heel retention force. Since, the cable pivot point is forward of the boot bellows where it’s bending, and the front part of the boot is being held down to the ski, the bellows is very soft and the cable isn’t too tight. Not sure though, but would be easy to know if you had it on your foot!
When I put soft leather boots in a hardwire cable it crushed my foot, painfully.

[Stephen]

If the cable is getting longer, the binding system puts pressure on the front of the ski.
I’m not saying how much pressure, just that some force is applied due to the mechanisms involved.

[TallGrass]

Yes, the cable mechanism gets longer as the spring in the cartridge is compressed. Where do we go from here?

I'm just saying I do not "see" any in the gif, nor TomT's video on full screen. And "spring ... is compressed" is ambiguous as for the same direction of movement a spring can be Compressed OR Stretched depending on design.

This particular case seems like it might not have any downward heel retention force. ... When I put soft leather boots in a hardwire cable it crushed my foot, painfully.

Agree, this instance may have little to no downward from the cable, or the boot is too soft in relation to spring force. Cables on my leather boots didn't crush (binding photos earlier in thread) and there was progressively more resistance with flex, clearly more so than my Rota' 3-pins.

If the cable is getting longer, the binding system puts pressure on the front of the ski.

More or less, I concur.

As for "where do we go from here?" I'd say...

Given the myriad of possible geometries and designs, it is perilous to discuss this kind of thing without a common reference image of boot+binding, same as thinking everyone will visualize "apples" in a fruit discussion and not oranges, peaches, or tomatoes.

Otherwise you end up with Six Blind Men and the Elephant!

A group of six blind men heard that a strange animal, called an "el-e-phant," had been brought to the town which none of them knew about. So they sought it out, and its handler began guiding them over to it.

"An elephant is like a thick snake!" said the first, whose hand landed on the trunk.

"No, it is like a fan," said another whose hand reached its ear.

"More like a tree trunk," said the one whose hand was upon its leg.

"How can you confuse a wall for that?" said the blind man who was feeling the elephant's side.

"Or a rope for a wall?" said the fifth who happened upon the tail.

The last let out a gasp of surprise when he encountered the tusk, saying, "All your joking trying to mislead me, nearly let me get impaled by this spear-like creature!"

Then the deaf man wrote, "Five hundred posts is a good stopping point for a thread, no?"