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Surgical tubing stretched too far
We have a catapult powered with surgical tubing on our bot. The tubing is stretched from about 5 inches untensioned to about 20 inches as the winch pulls down the catapult arm. That's a 300% increase in length.
During the Hub City regional, we suffered from frequent decreases in shooting power and had to re-tension the tubing several times over the three days, and we ended up replacing some of it. I suspect that the tubing is being stretched past its elastic limit. It displays "stretch marks". We can modify the bot's superstructure to allow for a much longer untensioned length on the tubing, reducing the extension from 300% to about 100%. Does this sound like it will solve the tubing over-stretching problem? |
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Re: Surgical tubing stretched too far
Had same issues a few years back until we went to spear gun tubing.
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Note that while the equation for potential energy of a spring is E=.5*k*x^2, note that the k value for surgical tubing isn't constant as you stretch the surgical tubing. I would do some quick tests to determine the force required to deform to a certain length. |
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http://www.amazon.com/Speargun-Sling...peargun+tubing |
Re: Surgical tubing stretched too far
What Keegan said.
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We have tried a couple of different ones and are also happy with the 1/2 OD and 3/16 Wall. |
Re: Surgical tubing stretched too far
On team 900 we've used surgical tubing power our catapult and we can shoot ~45 feet. We made sure to build it so that there's only 100% to 150% extension and we've not had to re-tension the surgical tubing.
So yes, it sounds like that probably will solve the over-stretching problem, but you'll probably have to tweak the # of wraps or something until it goes the distance you want. |
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We ran the McMaster tubing at our first competition and it definitely showed some wear and caused some issues in eliminations, I am wondering if the spear gun tubing will be better. |
We have been using 3/8 bungee to power our catapult. We found that it holds it's elasticity very well and we have yet to replace it.
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There are many variables to what causes wear, such as attachment points and stretch %. |
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Specifically, we've used both 12mm (1/2") Spear-it tubing, which seems to be identical to 1/2" OD, 3/16" wall latex tubing from McMaster. |
Re: Surgical tubing stretched too far
Another option, we went with the fitness bands. Find the force and corresponding diameters that work for your application and have fun. Our experience was a band reached its "advertised" force at approximately twice its original length. The brand carried by the chain sporting goods stores around here sells them in increments up to 100 lbs.
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Re: Surgical tubing stretched too far
We are very happy with the 'KOP' linear force springs from Vulcan
Hundreds of shots, no change. |
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