Elevated Bridge B/C

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smartkid222
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Re: Elevated Bridge 2009

Postby smartkid222 » January 3rd, 2009, 2:13 pm

Yeah, i'm doing really bad. And competition isn't that far away....
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Re: Elevated Bridge 2009

Postby dudeincolorado » January 3rd, 2009, 2:48 pm

my bridges are ...no
SO stressed!

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Re: Elevated Bridge 2009

Postby Keyreaper » January 3rd, 2009, 8:00 pm

The glue I use is a wood glue called Titebond III... Requires clamping (I use pins) and a full 24 hours to "set" and "harden"

Guys understand that this is a little different than the regular bridge building they did back ago. It is a little tougher. And that though hard work and failures, will come success. So far I've had a bad luck on my first 3 bridges. But because I am confident I know what I'm doing, I'm sure to get a good score. And If I don't get a good score. Try something a little different. :D Good luck :)
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Re: Elevated Bridge 2009

Postby sr243 » January 5th, 2009, 6:28 pm

just a thought, since most bridges break in the middle somehow whether it bends down too much or it snaps, y not just build the middle part. Through my test, i found out it broke around the same weight when i built the whole structure and the middle section. The sides do not receive as much stress therefore, it should not break. If sides do break, it would break and the middle part should remain almost intact falling into the bucket. If you want to increase strength efficiently, is this a fast method to test more?

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Re: Elevated Bridge 2009

Postby smartkid222 » January 5th, 2009, 7:03 pm

i'm not sure if what your saying is correct. Are your sides slanted(/ \) or straight(like a pillar)?

And you do realize that you need the sides for the bridge to be "elevated"?
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Re: Elevated Bridge 2009

Postby Keyreaper » January 5th, 2009, 8:34 pm

In my opinion. Instead of having the the legs like pillars. You should have them slanted... I think this because, One when slanted the middle section (where you load the loading block & the place above the clearance block) is definitely shorter, saving weight. And second, because they are at an angle. There is a little more stress going outward then just directly down. When going outward. the weight can be distributive. Going directly down, most stresses are on the main pieces. And there is just a truss in that section to keep the main piece from buckling. I suggest using a 70 degree angle, as that proves the best between outward and directly down. And for the person who said that the middle kept on breaking. This is another reason to have slanted legs. There is less stress applied to the middle and more stresses applied over the whole structure.
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Re: Elevated Bridge 2009

Postby Keyreaper » January 5th, 2009, 8:44 pm

Okay so I have two sides of these. But I don't know how to correctly make them stand up, so i can glue the lateral bracing. I was thinking of getting a block about 50 cm long and maybe 4-3 cm high and 5 cm wide... and just clamp both sides so that they are lined up.... But I'm afraid this will bend the balsa... Should I glue it??? Or if you have a better idea could you tell me??? Thanks :)

Oh yeah... and here's what the side looks like
http://www.facebook.com/photo.php?pid= ... 1513803783

I have tried composing a arch bridge mix.... and have it bottom loaded... turns out... It fails in torsion wise... although i haven't considered re-editing the design so it is top loaded... and see if it still fails in torsion.... Heres what it had looked like before I destroyed it... I was able only to get the picture of it while i was building it because batteries were dead and I never decided to recharge them...

http://www.facebook.com/photo.php?pid=3 ... 1513803783
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Re: Elevated Bridge 2009

Postby hogger » January 6th, 2009, 10:09 am

Okay so I have two sides of these. But I don't know how to correctly make them stand up, so i can glue the lateral bracing. I was thinking of getting a block about 50 cm long and maybe 4-3 cm high and 5 cm wide... and just clamp both sides so that they are lined up.... But I'm afraid this will bend the balsa... Should I glue it??? Or if you have a better idea could you tell me??? Thanks :)
We use foam board that you can get from art supply store. You can easily cut it to the shape that you want. Depending on where or how the loading block will be situated on your bridge, get multiple pieces of foam boards with different thicknesses and glue the right ones together to form the right thickness. The pieces should be cut before gluing because it is much easier to cut thinner piece of foam board. The shape we make looks similar olympic medal stand, with the top cylinder having a dimension closed to 5cm x 5 cm cross-section to allow for precise shape of the platform for the loading block. If you plan on doing top loading, this last part is probably unnecessary, you just need to make sure the 2 sides are vertical and and have proper spacing less than 5cm between them. The nice thing about foam board is that you can pin the sides onto it just like when you build them on the building board.

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Re: Elevated Bridge 2009

Postby smartkid222 » January 6th, 2009, 1:59 pm

and 5 cm wide...
making the space 5cm would be too small, it needs to be 5cm including the wood.
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Re: Elevated Bridge 2009

Postby Keyreaper » January 6th, 2009, 2:41 pm

turns out... its only 2 cms wide... LOL... I never checked... Not good... Should I take it apart and reglue it so it is 5 cms???
I think it has a chance of falling over.... But if it doesn't then it will surely fail in torsion... I'll get a picture up on here as soon as i can. :)
Oh yeah :) 500 posts on the Elevated Bridge 2009 topic... Good Job guys :P
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