Crossbow explanation needed.

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windhorny
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Crossbow explanation needed.

Post by windhorny » Thu Feb 16, 2006 3:34 pm

I have had my xbow since the day it came out but I never bothered to really look at how it works until I looked into the bar mod. This may take an engineer to explain this to me but I am curious how the pulleys actually give any mechanical advantage if they are not strung in the same way a typical 2:1 pulley works. I started to trace every line and movement and can't figure out for the life of me how the pulleys on the bows make it easier to pull. To top it off, when checking out the drawings on kiteforum about the bar mod, I realized that the pulley they want you to add doesnt seem to move at all. There was discussion of how the pulley might move only 2cm max on the line it travels on. If the line doesnt move through the pulley and it only travels a max of 2cm then what the hell does it do!? I am one of those guys that has to know how things work and I am truly baffled on this one.

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Post by Bullroarer Took » Tue Feb 21, 2006 5:25 pm

The pulleys on the Xbow don't give you mechanical advantage in the classic sense which is to reduce load at the expense of travel, but rather they work reverse of this. The Xbow bar gives twice the depower (if you move the bar 1 foot, the back lines become 2 feet longer), but now the load on the bar is twice as strong. This is one of the reasons that people complain about bar pressure on the Xbow. (I suspect not the only reason however since back line pressure is not only caused by bar design.)

So you are right, the pulleys don't make it easier. They make it harder.

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Post by Greg » Wed Feb 22, 2006 1:11 pm

Hello Horny One,
Seemed to me: bar pressure was 2X as heavy, steering is 2X as loose.
BTW: Thanks for letting me demo your X-bow, I'll let you try my ShockWave and you can tell me what you think of NAISH's version of the S.L.E. design. They did a stopper ball thingy that reduces the bar pressure for cruizing...
See you soon,
L.M.G.

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Post by andyandmarlys » Wed Feb 22, 2006 7:10 pm

LMG...

I am always interested in trying out different kites, and the shockwave is one that I have been curious about. A couple of days ago I Yuri and I swapped kites back and forth (his CB 12 and my TD 12) and I learned a few things..

It seems the CB is open slightly wider than the TD.. Ie, the CB seems a bit flatter than the TD. Both were able to turn fast, but it seemed to me that the fast turning was more easily initiated on the TD...maybe because of a shorter bar, or perhaps because it is not quite as flat as the CB. The CB bar is certainly bigger in almost all aspects... girth, lenght, weight...but I think the biggest thing that I noticed was the bar pressure with no way to rest your arms on a stopper ball. Had the kite been setup with a powerlock, I think I would not have minded that much, but it wasn't. If I were a CB owner, mechanical advantage or not, I'd seriously look into the extra pulley... or at least the powerlock.

A

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Post by windhorny » Wed Feb 22, 2006 9:43 pm

thanks for the explanation. that makes sense. As a result, i just bought a Turbo Diesel. Go 1 pump.

So, I found another flaw in kitesurfing...


IT REQUIRES WIND!!!!

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