Scioly.org

I have a question about what size wood trusses are you guys using. My bridge is mainly made out of 1/8 by 1/8 pieces of balsa wood. My question is should I use 1/16 by 1/16 bass or balsa trusses or use the same 1/8 by 1/8 balsa wood as truss members?

I just tested my bridge again and it held 8 kg, giving it an efficiency of 534. It's not as high as my best score, but this design is definitely something I can improve on. The main frame of the bridge was intact, so I'll just reuse that. I'll probably be able to test again tomorrow.

Balsa Man, I just looked at your safety tower post. I have to say that that's a very clever idea. It's basically loading the bridge slowly so that at the first break you can see it, if I understood correctly. After competition, I might try building one. It's a very neat idea and probably the best way to see how your design does. How'd you come up with it?

croman74 wrote:The main frame of the bridge was intact, so I'll just reuse that. I'll probably be able to test again tomorrow.

You reuse bridge pieces?

Just for this bridge. I don't have much time for states, so I'm just reusing. I realize that it affects it a little, but this will be the last time I use it.

what are your top efficiencies?

croman74 wrote:Balsa Man, I just looked at your safety tower post. I have to say that that's a very clever idea. It's basically loading the bridge slowly so that at the first break you can see it, if I understood correctly. After competition, I might try building one. It's a very neat idea and probably the best way to see how your design does. How'd you come up with it?

Croman,
Its not loading it slowly - you load it at whatever rate you want to. Its that the chain from the top of the tower, down to the load block, which has just a little slack in it, controls how much the load block can drop when the bridge fails. Instead of the block falling.....all the way through the bridge and into the bucket, it falls like 1/8th inch (whatever you've set it to), and then it stops. Depending on where/how the bridge failed, the damage is usually limited to the initial failure mode - no secondary damage. So, not only do you really see how your design did - where and how it failed, you can usually "patch it up" (like splint - as in gluing lamination strips on) where it broke - and beef up .....coresponding parts - like if a leg buckles, splint it and the other 3, and quickly re-load, and see if there is another member that's not strong enough to hold full load. Repeat till you get to full load. On the next build, you KNOW which pieces have to be stronger, and about how much stronger - higher density, or laminated

As to how I came up with it; same process we're doing on this board- talking and sharing ideas; a friend who was helping coach at another school. That's why I've shared it here; its about learning. We've been using it for 3 years. First time we used it was when my son was in 8th grade. It was the key to a bridge that got just short of 2500 efficiency that year.

So, yeah, its worth playing with. Enjoy.

Should have some photos up on the Image Gallery soon.....hopefully tomorrow. Bridge, and tension and compression testing rigs, & jigs......

Len Joeris
Fort Collins, CO

I think I kinda get it. Are you going to upload pics of the safety tower as well? In the future, that's definitely an idea I'll play with.

Arthur -

Since it's what counts for you - I'd bet that for upcoming PA states, the winning efficiency for B division will be upwards of 1500. What won at regionals was only just above 1000. How are your bridges coming along?

our bridges are coming along pretty well. yesterday we tested a really good bridge and we were really excited about the efficiency we got.