Elevated Bridge B/C

[andrewwski]

Yup. 15 kg is pretty heavy - having a higher load would mean you'd need to either get denser material to load (hard to find) or a bigger bucket (harder to work with). Plus, carrying 33 lbs of sand around is pretty heavy already.

I'm glad that they don't use a tiered system anymore.

[dholdgreve]

Back in the late '90s I think it was a 20 Kg limit.

[Balsa Man]

It's somewhat surprising to hear how many top schools seem to have less than fantastic bridges this year... Not sure about Troy in CA, but Grand Haven didn't break 1500, none of the top Ohio teams broke 1500, Fayetteville Manlius in NY didn't, Penncrest in PA didn't, Poudre in CO didn't... maybe they've improved - we'll just have to see at nationals!

Hmmmm…. Very interesting…. wow, I wish was going to be able to make it to Nationals to watch. While our school’s not going, both Colorado teams are from here in Fort Collins – Poudre in C, and Blevins in B, so I’m pulling for the old hometown to show well. Right after winning at State, Peter had some great discussions with the builders from both schools – both about design and construction; what worked well, what didn’t work. That led to the opportunity to consult with both in preparation for Nationals – a chance for both them and us to expand our knowledge, and build on past learning. Good coaching experience, good student experience. It’s sort of the essence of how science – and engineering - works; a body of knowledge that keeps expanding, with today’s advances coming from and standing on the shoulders of yesterday’s. Part of what this forum does, too.

Its been interesting over the years watching the mix of secrecy and openness regarding the balsa (and other) building events. We all get to see what’s happening in our respective States, but even there, some people get ouchy about people taking photos, or even wanting to look closely [shades of the (overblown IMHO) flap about the posting of Electric vehicle photos recently]. Others are more…..open, particularly with those that are struggling to figure out how to get better, and even to some extent with cross-town or cross-state rivals.

Particularly as one moves toward Nationals – and even after, getting a nation-wide sense of what’s being done and what’s out there is not very easy. The addition of the Image Gallery this year (thanks, Dark Sabre!) really helps; great resource. I’ve seen a number of “…their bridge, or tower, looked a lot like our Regional one…” comments over the years, suggesting there was something wrong with that. As I see it, being able to see examples (good and otherwise), recognizing good ideas, adapting them, improving them- that’s engineering at work.

To use an analogy from another competitive realm I used to play in, racing, when you show up at the track, and do well, people are going to be looking at what you brought. Photos get taken, word spreads. If there are parts, or ….configurations that seem to be contributing to success, you expect to see other people’s versions of or takeoffs on them next time….

So, as I said at the outset, its going to be most interesting to see what the various teams can do between now and then to improve on their State efficiencies. The numbers from folk that are not going – and a few that are – give a sense of what’s possible.

Peter’s design, as I posted earlier, has room to come down in weight; at 10 gr, it was significantly over-built, and we have a good handle on about how much and where. His design is readily modified to B Div specs – a very interesting exercise that sheds some light on earlier discussions as to whether B or C should produce higher efficiencies. Looking at what happens to forces in the structure when you modify it to B Div specs highlights some interesting trade-offs. The same height, but shorter span, means less wood. But, with the smaller/narrower truss height, higher forces along the top and bottom, but, shorter members/exposed column sections….. In the end, somewhat lower weight than the C configuration.

So, while recognizing the possibility of one or two “amazing ones” showing up, I think near the top - say the average of the top 6 - we’re going to see slightly higher B efficiencies. The numbers could be a little different with different designs, but for B & C versions of our bridge, the B has a little over a 10% advantage.

Looking forward to hearing reports from Nationals- good luck to all!

[Aia]

I'm excited to watch the bridges at Nationals. After the season is over, I'll post 35 to 40 of my bridges that I've built between July and now to the image gallery. (I think the real limit on how many pictures I post will be how much space Dark Sabre will let me take up on the photo gallery, haha). This is my last year, so I'll be happy to share them once the season is over. Hopefully others can build upon some of my work!

Who all here is testing a bridge in Georgia?

[croman74]

Good luck to you at nationals! Your pictures are greatly appreciated. I'm sure everybody could benefit.

[Dark Sabre]

I'm excited to watch the bridges at Nationals. After the season is over, I'll post 35 to 40 of my bridges that I've built between July and now to the image gallery. (I think the real limit on how many pictures I post will be how much space Dark Sabre will let me take up on the photo gallery, haha). This is my last year, so I'll be happy to share them once the season is over. Hopefully others can build upon some of my work!

Who all here is testing a bridge in Georgia?

You can have your very own subgallery

Good luck!

[cypressfalls Robert]

does anyone know if, at nationals, you will have to pour the sand by hand or by a machine?

[croman74]

I'm guessing that it will be by machine. I imagine that at nats, everything runs smoothly and effectively.

[smartkid222]

i think they use the same hopper as they use in NY: http://www.newyorkscioly.org/SOPages/Newsletter1.html I'm not sure though.

[Bjsong]

I never used a hopper system so my question is how does it work because I'm going to nationals but I always used a scooper and a bucket and load manually.