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which is better? bass or balsa for elevated bridge?

smitherzz6 wrote:which is better? bass or balsa for elevated bridge?

Generally a mix of both. All depends on your design. Balsa is lightweight but bass is higher density. However balsa typically is stronger for the weight. So test your design, and if you need a density/strength balsa can't get, try out bass. All balsa designs have done well and all bass designs have done well.

smitherzz6 wrote:which is better? bass or balsa for elevated bridge?

You can look in the archives, there have been lengthy debates on this, pros and cons for both. Personally I'm a fan of balsa, but it really depends on preference and design.

Yeah, there were a couple discussions on it. Also check the wiki page, there's some stuff there about the two. Very strong bridges have been built out of both, or a combination of the two. Your design will affect the kind of wood you will use.

smitherzz6 wrote:which is better? bass or balsa for elevated bridge?

a general question. if u check the older thread there are pages devoted to this.
for me, I generally like balsa wood better.

I need a few suggestions on how to improve my design....anyone?

So basically, my bridge has a A frame and there are two parallel beams on the top, designed to hold the legs from expanding outward. (They undergo tension....I think)
I have been using 1/16x1/8 in pieces to build these parallel bars. It looks a bit like this (this is just showing the top; the problem members are red):
.. _________
/____________\

From the side, you can see both pieces that sandwich the leg member in each joint, located at each corner of the trapezoid shown above. I []I The red pieces are the thin pieces I'm talking about.

However, when I tested, my bridge has a problem in which the top began to distort. The thin members I used were able to hold the weight, but they deformed, breaking the top of the bridge. I'm not sure whether to make this an I beam or add specific pieces to reinforce the member....and suggestions??

If its more helpful, I could upload a picture...

Yes, please upload a picture.

Hm...Anyways, I think 1/16 by 1/8 is a little too small to build the parallel bars out of. Maybe 1/8 by 1/8 would deform less. And are you putting in any bracing between the 2 parallel bars? If not, I'd put some in the middle of the span to keep the top from bending too much.

Also, what exactly is the problem? Are the legs sliding outwards too or is the top span just bowing while the bottom one stays (more or less) straight? The more I know, the more I can help.

*Disclaimer: I am in Div. B...but the basic principles should remain the same.

13bridges wrote:I need a few suggestions on how to improve my design....anyone?

So basically, my bridge has a A frame and there are two parallel beams on the top, designed to hold the legs from expanding outward. (They undergo tension....I think)
I have been using 1/16x1/8 in pieces to build these parallel bars. It looks a bit like this (this is just showing the top; the problem members are red):
.. _________
/____________\

From the side, you can see both pieces that sandwich the leg member in each joint, located at each corner of the trapezoid shown above. I []I The red pieces are the thin pieces I'm talking about.

However, when I tested, my bridge has a problem in which the top began to distort. The thin members I used were able to hold the weight, but they deformed, breaking the top of the bridge. I'm not sure whether to make this an I beam or add specific pieces to reinforce the member....and suggestions??

If its more helpful, I could upload a picture...

Is the loading block placed directly on top of the top red piece?

Hm.

I'd have to see a picture, because it's tough with the diagram you provided... but it seems very unlikely that the top horizontal members of an A frame bridge would ever be in tension. I do think you can hold the force with a 1/16 by 1/8 piece though if you design it right - a picture would definitely allow me to help more!

I'm uploading the pictures but it might take some time.
These are post testing so you can see where the breakage was.
Also, photography isn't my high point so I hope you can see whats going on.