Telemark Talk / Telemark Tips Forum

GrimSurfer wrote: ↑

Wed Jan 11, 2023 3:56 pm

jalp wrote: ↑

Wed Jan 11, 2023 3:40 pm

GrimSurfer wrote: ↑

Wed Jan 11, 2023 3:19 pm

Leverage requires a lever and a fulcrum.

True, yet I propose that the cable in combination with the boot sole, is effectively, a lever system. It's a springy, bendy kind of lever but a lever none the less.

So, where is the fulcrum in this system? Well, it should be at the ball of the foot. My proposal assumes that the skier is using good form, keeping the BOF down. If the BOF is down, the fulcrum is at the BOF of the boot sole. Remember, a fulcrum is much less a thing, than it is a place.

Once you say “spring”, you’re back into a net force deal… input force = output force, ergo net force = 0. Fortunately, you’re using the NASA term “springy, bendy kind of lever”.

I agree that the fulcrum could be the ball of foot. But this would be problematic because we’re back to a force and mass discussion (since all force exerted by the skier based on mass transfer goes through the ball of foot anyway when the heel is raise. So what is the net benefit of the cables, from a force perspective?

These are some of the problems one is confronted with when looking at the cable as a lever, spring, etc.

Things would be so simple and easy to define were it not for so many dynamic and flexible components in the system. If that were the case, we could just call it Alpine Skiing and move on...

jalp wrote: ↑

Wed Jan 11, 2023 3:40 pm

GrimSurfer wrote: ↑

Wed Jan 11, 2023 3:19 pm

Leverage requires a lever and a fulcrum.

True, yet I propose that the cable in combination with the boot sole, is effectively, a lever system. It's a springy, bendy kind of lever but a lever none the less.

So, where is the fulcrum in this system? Well, it should be at the ball of the foot. My proposal assumes that the skier is using good form, keeping the BOF down. If the BOF is down, the fulcrum is at the BOF of the boot sole. Remember, a fulcrum is much less a thing, than it is a place.

Of course.

@mca80, hang on, we are coming for you. Don’t give up hope.

35, I have 35.
Do I hear 36?

Yes alpine skiing! So much simpler and easier. I have AT gear…. You can fix the heel and lever onto the ski tips! Same with cable tele bindings but there is some movement and springiness involved.

If you leave the heel unlocked, it’s really a handicap.

Hope that helps!

jalp wrote: ↑

Wed Jan 11, 2023 4:19 pm

GrimSurfer wrote: ↑

Wed Jan 11, 2023 3:56 pm

jalp wrote: ↑

Wed Jan 11, 2023 3:40 pm

True, yet I propose that the cable in combination with the boot sole, is effectively, a lever system. It's a springy, bendy kind of lever but a lever none the less.

So, where is the fulcrum in this system? Well, it should be at the ball of the foot. My proposal assumes that the skier is using good form, keeping the BOF down. If the BOF is down, the fulcrum is at the BOF of the boot sole. Remember, a fulcrum is much less a thing, than it is a place.

Once you say “spring”, you’re back into a net force deal… input force = output force, ergo net force = 0. Fortunately, you’re using the NASA term “springy, bendy kind of lever”.

I agree that the fulcrum could be the ball of foot. But this would be problematic because we’re back to a force and mass discussion (since all force exerted by the skier based on mass transfer goes through the ball of foot anyway when the heel is raise. So what is the net benefit of the cables, from a force perspective?

These are some of the problems one is confronted with when looking at the cable as a lever, spring, etc.

Things would be so simple and easy to define were it not for so many dynamic and flexible components in the system. If that were the case, we could just call it Alpine Skiing and move on...

I agree, @jalp

I'm glad we're all in agreement that the ball of the foot is the fulcrum.

"the" or "a"?

Sometimes there is one major fulcrum when the boot is on a frame as shown here, the steel pin hinge in plastic ...


... and other times two fulcrums as seen here with one being the cable pivot at the ski binding and the other being where the sole of the boot is flexing (about an inch or so behind cable pivot) with crinkles radiating from it. It's easy to see a triangle, and thus a third pivot where the 'cable' wraps around the heel and rotates in the plastic clip. While near, the ball of the foot (BotF) is going to slide like the pages of a phone book atop the sock bed, and it over the insole, and it over the top of the sole (or bottom of the last, depending on construction ... for that annoying squeak), when bent. The BotF is NOT be the fulcrum/pivot of the boot+binding+ski* because the sole would then have to stretch around the ball-of-foot circumferentially (damn, that'd hurt!).

Were there not two pivots, you could likely toss the spring for a lighter threaded rod, yet since there are two pivots, a fixed rod would lead to the tension swinging from spot-on, to too-tight, or slacking-off and freeing the heel clip.


Relatively speaking, the triangle leg between the sole-pivot and cable-pivot stay fairly fixed.
Like a snap-hairpin or bi-metalic strip, there will be a "cam over" point, unless designed in way where the two shorter legs of the triangle do not pass through (their sum = length of third leg) the third (such as the ski limits the heel from passing through).

A triangle (with two variable legs) attached to the middle of a long lever, now THAT's a fun Free Body DIagram or FBD (for someone else) to play with!

* Yet, the BotF is a skeletal pivot (and its human both the Accuator and Conductor of this music), attached to muscles, tendons, and ligaments making another triangle (two bone legs, one 'muscle' leg) in the forefoot -- a FBD of a Forefoot Triangle interlaced with a Boot/Binding Triange, the former which is attached to an Ankle Triangle, and it a Knee Triangle, and it a Hip Triangle.

Now who wants to draw up THAT Five Triangle Free Body Diagram! I bet some CAD and CGI savvy blokes can!

This thread has me kinda starting to believe in perpetual motion…

I’d be thrilled if that snow dump eastern Canada decided to go west.