variable side-cut radii...advantage...purpose?

[Tanglefoot]

17 hours ago, BlueB said:

You can't just put a variable on top of radial and decide "it's only 1mm difference...". Your best bet is measuring and calculating the various segments of variable one, piece by piece. 

 

I'm really interested how are you going to measure the last 3 variables, you mentioned... Especially the natural frequency... 

A very valid point, and now that I have had some sleep, I have taken appropriate action. I am finding that it is very difficult to accurately measure a large radius over a short length, but I have made an attempt by checking 300 mm segments at the nose, middle and tail. By converting the height of each segment into a radius, I found that the nose had a 7 m radius, the middle had 11 m and the tail had 9 m. Go figure.

With regards to measuring flex, damping and natural frequencies - I think it is reasonable to compare similar boards this way, but it is by no means an industry standard: Place the boards on supports near the tip and tail (same spacing for both boards), put some weights in the middle and measure the deflection. This does not give you the flex pattern, but it gives an idea of the overall stiffness.

I have a vibration analysis app on my phone. I leave the boards on the supports as before, and cause the boards to vibrate by rapidly removing the weights. The app then measures the natural frequencies, and gives a good idea of the time it takes for the vibration to die out. Not super-scientific, but quite interesting. 

[Corey]

1 hour ago, Tanglefoot said:

Place the boards on supports near the tip and tail (same spacing for both boards), put some weights in the middle and measure the deflection. This does not give you the flex pattern, but it gives an idea of the overall stiffness.

You just discovered the number in the middle of the Coiler code!  ;)  

I joke, but don't mean to detract from it.  It's clearly an important measure.  What's surprising to me is how we generally obsess over getting exactly the right flex for Coilers, and yet I lost 50 lbs and can ride all but one of my Coilers that were made for my previous weight with no ill-effects.  The big stiff NSR?  Well, it didn't turn unless I practically jumped on it.  Luckily, it's found a new home!  

And then there's Donek, who doesn't do weight-specific boards.  Maybe I'm wrong on that...  They seem to work just fine for everyone.  I don't get it.  

[lowrider]

I believe the fundamental reason vsr is desirable and so effective is that it allows differing front and rear widths that a single side cut radius does not allow as far as design and build are concerned. The paramount  issue of where you can place the bindings with respect to mid point (balance point)  of the board is limited by a single side cut radius. By blending many side cuts you are free to position the binding in the ideal location that a single scr does not allow.

[Neil Gendzwill]

1 hour ago, corey_dyck said:

And then there's Donek, who doesn't do weight-specific boards.  Maybe I'm wrong on that...  They seem to work just fine for everyone.  I don't get it.  

It's because we are hopefully not dead weights.  You had to "jump" on your NSR to get it to work with your svelter (is that a word?) self.  The others you probably needed to work a bit harder too, I expect they were just more in your by now near-automatic range of "need more turn, add more input".  You are also probably stronger now, being that you lost that weight by picking up heavy stuff and putting it down again repeatedly.  That will help you bend stiff boards too.

If a board is stiff enough that we have to work super-hard to get it to turn, or it doesn't turn much for us, we pronounce it "too stiff".  If the pressure from standing on it turns it into a U we say "too soft".  I expect the range in between those things is a fair pile, and as evidence I present the broad recommended  weight ranges of most manufacturer's boards.

Edited March 30, 2017 by Neil Gendzwill

[wulf]

7 hours ago, lowrider said:

I believe the fundamental reason vsr is desirable and so effective is that it allows differing front and rear widths that a single side cut radius does not allow as far as design and build are concerned. The paramount  issue of where you can place the bindings with respect to mid point (balance point)  of the board is limited by a single side cut radius. By blending many side cuts you are free to position the binding in the ideal location that a single scr does not allow.

on the spot !

[Corey]

11 hours ago, Jim Callen said:

If you get a custom board, every single one is built to the rider's weight, unless they want the stock flex.  What don't you get?

Oh, interesting.  I completely misunderstood!  I thought there was one flex and that it worked for all.  

[BlueB]

On 30/03/2017 at 1:18 PM, Tanglefoot said:

I am finding that it is very difficult to accurately measure a large radius over a short length, but I have made an attempt by checking 300 mm segments at the nose, middle and tail. By converting the height of each segment into a radius, I found that the nose had a 7 m radius, the middle had 11 m and the tail had 9 m. Go figure.

Awesome, it's a VSR! :) 

[west carven]

howdy

single radius is all you need for a clean carve. vsr is not for good technique and not a perfect carve...

doneks radical vsr is not for making clean carve, but for shooting out of a carve... perfect carve is single radius...

[BlueB]

On 30/03/2017 at 1:18 PM, Tanglefoot said:

Place the boards on supports near the tip and tail (same spacing for both boards), put some weights in the middle and measure the deflection. This does not give you the flex pattern, but it gives an idea of the overall stiffness.

We did this many years ago... search BOBSI or ULFI... I believe Coiler does something similar, too. 

[Eric Brammer aka PSR]

1 hour ago, west carven said:

perfect carve is single radius.

Only true if you don't influence the turn As It Occurs! I adjust as I need to, and can do Kurt Hoy imitations as I need to, but also can often stay just off of RipTurns' [CMC] line. But, hey, if you only ride 'perfect' snow, on a 'perfect' pitch, you'll be 'perfectly' happy.  I like being challenged by having made some 'nice' turns, then, going on and making ten "better".

I've done 'perfect' turns about 3-4 times

[philw]

The idea that people should ride to conform to some limited and probably incorrect mathematical model is to confuse snowboarding with figure skating.

Obviously it's not perfect if the snow doesn't break over your head and if the girls don't clap when you get to the bottom of the run and if someone doesn't buy me a beer, but to suggest that precision of the arc in conforming to some naive mathematical model seems somewhat confused. Ride more, think harder.

 

[partner0]

On 3/20/2017 at 8:20 PM, Jack M said:

Parabolic and Quadratic are the same thing.  A parabola is drawn from a quadratic formula.

http://www-history.mcs.st-and.ac.uk/Curvepics/Parabola/Parabola1.gif

I distinctly remember reading a Transworld interview with (Paul? Peter?) Wren during the 1990 season where he described Burton's new quadratic sidecuts.  He said picture a rope hanging between two points. That would technically be a catenary curve, but he was just illustrating that a quadratic (parabolic) sidecut is tighter in the middle and longer at the ends.

Actually the curve described by a uniform rope hanging between two points and acted upon by the sole force of gravity (locally uniform), is not a parabola. It is called a catenary, and is mathematically represented by the hyperbolic cosine function. Who would have guessed this math class I never used as an old fart engineer would end up serving a purpose, albeit a négligeable one, on a racing snowboard forum.