Johan Baarman wrote:
> Micah Stevens skrev:
>   =

>> You wouldn't want to measure absolute speed, you'd want to measure =

>> acceleration. Otherwise you'll get wildly different results unless you =

>> could test it at the same point in the slide each time. i.e. after =

>> exactly 1 foot. Looking for acceleration would make this easier, just =

>> measure twice and get the ratio of the two.
>>
>>   =

>>     =

> I was thinking of only timing how long it would take to go from point A =

> to B. I know that there are systems out there that do this but I would =

> like to make one of my own. I=B4ve heard that an old one just used magnet=
s =

> digged into the skitrack and an timer started and stopped by an =

> reedrelay but I think that this approuch is rather inaccurate. I was =

> thinking of an irda fitted to the skiers leg sending out a signal, when =

> reflected the first time would start the timer and stop the second time. =

> The skier must of always start at the same point of course.
> This is how I thought it would look like:
>   =

Yes, but this will change unless you have a great amount of control over =

the initial conditions of the test. I'm completely ignoring the variable =

that the snow itself imposes on the experiment. By measuring =

acceleration, you might be able to get past that requirement.

It's really a tough problem actually, now that I'm giving it some =

thought. I mean, how much will the quality of the snow affect the =

performance of the ski? You'd want to test each ski on a virgin patch as =

as more than one ski goes over a patch, it will change the friction of =

the snow itself, therefore skewing your results.

You might do better with a unit that straps to the ski itself, and uses =

a sonic sensor to measure speed/acceleration via doppler shift. Then you =

just attach it to the ski, and toss the ski down wherever you feel is =

appropriate, instead of having to have some sort of test fixture to deal =

with.

-Micah
-- =

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