Accurate, replicable method of measuring ski flex (long)

For discussions related to ski/snowboard construction/design methods and techniques.

Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp

Svimen
Posts: 27
Joined: Thu Apr 06, 2006 3:13 am
Location: Trondheim

Post by Svimen »

The ideas I presented earlier have nothing to do with finding the "perfect" flex, but rather finding a close approximation to the real forces acting on the ski. The approximation is never going to be perfect, and it will anyway have to be adjusted for different types of snow and even different climates. (Norwegian pow is not like the pow in the Rockies...)

Assuming most people here are most interested in off piste skiing this leads to an idea for measuring the hardness/density of the snow. Taking for instance a plywood board of 1 square meter and loading it in a uniform way with 100 kilos, and then measuring the depth of the depression in the snow might be one way of doing this. (Any other ideas not involving a large piece of plywood and heavy weights would be most welcome.) This might then give some indication of the type of forces acting on a ski in different types of snow. (Measuring in different conditions along with some qualitative (Measuring the density directly kg/liter might also be valuable) input might give some values for quantifying different conditions (champagne, soft, windpack ++) much like a grading scale in climbing.)

I think this sort of thing would be useful for comparing impressions on how a ski rides even in a global community such as this.

On another note: Has anyone done any real measurements of forces while actually skiing? I have an idea for equipping a ski with two pressure sensors under the boot (toe and heel) along with an accelerometer and hooking everything up to an arduino board (www.arduino.cc) and then riding with a computer in my backpack, logging data in different conditions. You could even use small strips of piezoelectric material to measure the tension and compression forces on the ski. This might then provide some certain figures when it comes to the forces acting on the ski, and again give some feedback to how we test the flex characteristics of the ski.


Svimen

Do I sound like a raving enginerd? :D
User avatar
endre
Posts: 413
Joined: Sun May 01, 2005 8:51 am
Location: norway
Contact:

Post by endre »

this is getting scary, svimen, have you been in my mind?

I did a diploma on custom skis last spring, and all the things you mention I have either done or planned to do. I did a lot of "snow resistance" testing last year, it is based on the same general principle you mention.

I have started building a ski with electronic flexing sensors built inside, they measure how much you actually bend the ski while skiing.

the sensors look like this,and can be connected to a recoding unit:
Image

I imagin using this ski as an analyzing ski, to test skiers, and how they pressurize the ski in different conditions
G-man
Posts: 600
Joined: Sat Mar 25, 2006 3:58 pm
Location: northern sierra nevada

Post by G-man »

Hey guys,

I don't know if you have seen this article from telemarktips. I know it's not exactly what you are talking about, but some if the technology is similar.

www.telemarktips.com/ForebodyPress.html

G-man
blissard
Posts: 4
Joined: Mon Nov 21, 2005 7:37 am
Location: Trondheim, Norway

Post by blissard »

Being a cybernetics engineer I've thought about "ski instrumentation" a few times myself. But haven't even got around to building a ride. I'd be surprised if the bigger ski companies haven't done something like this at some point in time, though.
sinful and wind-borne
Svimen
Posts: 27
Joined: Thu Apr 06, 2006 3:13 am
Location: Trondheim

Post by Svimen »

Haha, I have not been in your mind Endre, I have only been discussing ski characteristics with a friend, and we are in the early stages of trying do build our own skis. (Deciding on when to start doing the ski press seems to be pretty hard.)

Our original reason for testing the flex characteristics of different skis is that we thought it would be cool to offer custom skis to people based on their own design input. (After skiing a lot of demo skis last winter, we constantly argued over how different skis should be improved/combined. We both wanted Völkl mantras with real tips in both ends for instance, or maybe a slightly stiffer maiden ak, more sidecut on the big trouble and so on.) I believe this also touches on your idea for skibuilding, but don´t worry, I think it is only a natural way of thinking if you seriously take the time to consider how skis and ski companies could be better.
Svimen
Posts: 27
Joined: Thu Apr 06, 2006 3:13 am
Location: Trondheim

Post by Svimen »

Blissard:

What is your take on instrumenting the skis? What ind of sensors would be most effective? (I can´t help thinking that a few precise accelerometers (tip, middle, tail (boot)) might give you a lot of really useful data?)

Pressure sensors under the boots will probably be quite hard to fit, and output might also be unreliable (due to snow buildup under the boot, pressure distribution between boot and binding and the varying angle in which pressure is applied to the ski from the boot)
blissard
Posts: 4
Joined: Mon Nov 21, 2005 7:37 am
Location: Trondheim, Norway

Post by blissard »

By the way, since Finite Element Analysis has been discussed here, I found a Ph.D. thesis which you may or may not be familiar with:
FINITE ELEMENT SIMULATION OF A CARVING SNOW SKI

Seems interesting at first glance.
sinful and wind-borne
blissard
Posts: 4
Joined: Mon Nov 21, 2005 7:37 am
Location: Trondheim, Norway

Post by blissard »

Svimen wrote:Blissard
What is your take on instrumenting the skis? What ind of sensors would be most effective? (I can´t help thinking that a few precise accelerometers (tip, middle, tail (boot)) might give you a lot of really useful data?)

Pressure sensors under the boots will probably be quite hard to fit, and output might also be unreliable (due to snow buildup under the boot, pressure distribution between boot and binding and the varying angle in which pressure is applied to the ski from the boot)
It really depends on what you want to use your data for. Some kind of pressure sensors will give you a lot of data, but I think there will be a lot of variables coming into play, aside from ski properties. Snow characteristics, rider style etc. I'm thinking maybe it could be useful for optimizing the way you pressure the ski during a run.

I think my original idea was more along with what Endre describes, to analyze ski flex/behavior in various conditions. But it's just small ideas in the back of my head, haven't looked at actual sensors. I'd have to build a ski press first 8)
sinful and wind-borne
MartinH
Posts: 15
Joined: Thu Apr 06, 2006 6:05 am
Location: Norway

Post by MartinH »

This is starting to get hight tech! Me like :D

I do agree that there’s no perfect flex, or perfect ski at all; we all have different preferences. However, I'm certain that making flex calculations combined with flex testing is the first step of how to make quantitative assumptions of ski characteristics.

Doing flex logging during riding is taking it to the next level! I’ve never heard about anything like that, but I would be surprised if they haven’t done something like that making racing skis. I believe a combination of snow hardness measuring, a flex analyzer and a slope with a uniform snow pack would make it possible to do “laboratory” tests. I believe this method also would make it possible to do realistic measurements of the skis damping coefficient.

Being a mountain biker I know the best racing teams do something similar. They mount logging equipment on their bikes to log the suspension action during training, making it possible to do the perfect racing tune.

Endre: The sensor you mention; is it possible to mount it on top of the ski as well? It would be interesting to be able to measure different skis on the same snow pack.
blissard
Posts: 4
Joined: Mon Nov 21, 2005 7:37 am
Location: Trondheim, Norway

Post by blissard »

whoa! Trondheim takeover! ;)
sinful and wind-borne
User avatar
endre
Posts: 413
Joined: Sun May 01, 2005 8:51 am
Location: norway
Contact:

Post by endre »

Endre: The sensor you mention; is it possible to mount it on top of the ski as well? It would be interesting to be able to measure different skis on the same snow pack.
They are a bit fragile, but if we protect them with some hard ass tape and ski carefully i'm shure it would work! they are about 10cm long and cost 200kr each, expensive to damage lots of them.

so where did all you trondheimguys suddenly com from? everyone just popped out! guess it was all this techno talk that lured you out eh?..
Svimen
Posts: 27
Joined: Thu Apr 06, 2006 3:13 am
Location: Trondheim

Post by Svimen »

Guess the lights went out late at NTNU yesterday!
They are a bit fragile, but if we protect them with some hard ass tape and ski carefully i'm shure it would work! they are about 10cm long and cost 200kr each, expensive to damage lots of them.
So: Does anybody know where we could get/borrow some heavy duty sensors? Should be lots of them around here on campus... I´m thinking maybe the machine engineering faculty. Unless you guys at the cybernetics lab have some that are built to last? (blissard?)

I think it would be cool if we could analyze lots of different skis, even before trying to build our own. We should develop a method that lets us swap the equipement from ski to ski quickly, and also some standard format for exchanging data with others. (That is: If there are any others (outside of norway) who are interested. Seems they have been scared away from this topic?)
User avatar
endre
Posts: 413
Joined: Sun May 01, 2005 8:51 am
Location: norway
Contact:

Post by endre »

Eirik Aalde did a lot of vibration testing with sensors put on tele skis. that was back in the good old asolo-days, when things really vibrated!

Anyway, just mentined that because he was a student at NTNU at that time, seems like you have a lot of different sensors around :)

would bee cool to hook up with you guys some day and test this!
Svimen
Posts: 27
Joined: Thu Apr 06, 2006 3:13 am
Location: Trondheim

Post by Svimen »

We could probably meet up at Oppdal some time this winter. Good to get some pressure on, so that the testing apparatus is actually built...

I´m hoping to get a cabin up there for the season, might make a good base for experimenting!

btw Endre: Is your diploma available for download somewhere? Would be a nice read in the afternoon...
User avatar
endre
Posts: 413
Joined: Sun May 01, 2005 8:51 am
Location: norway
Contact:

Post by endre »

It should, but is not. I can bring it if we meet at Oppdal.

My flex analyzer project depends of the rest of my project, I got lots of things to finish first, (I have this torsion-thing going on for Fri Flyt) but we cold meet anyway and make som plans
Post Reply