Surgical tubing stretched too far

[JohnSchneider]

Originally Posted by nixiebunny

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?

You'd probably need a stronger grade tubing since you'll get less energy stored with less extension (E=1/2kx^2). Unless you're modifying your superstructure considerably.

[Sunshine]

Had same issues a few years back until we went to spear gun tubing.

[tim-tim]

Originally Posted by Sunshine

Had same issues a few years back until we went to spear gun tubing.

Spear gun tubing, that sounds interesting. Care to share any details? Like differences, mounting, pricing, sourcing, etc.

[tim-tim]

Originally Posted by animenerdjohn

You'd probably need a stronger grade tubing since you'll get less energy stored with less extension (E=1/2kx^2). Unless you're modifying your superstructure considerably.

Yes, you will either need to switch out to a "stiffer" type of surgical tubing or add more strands of it; or both.

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.