Elevated Bridge B/C

[dragonfly]

While mass gain wouldn't be that big of an issue, the secondary effects of the moisture have wreaked havoc on my bridge. My entire bridge has now become torqued. When I left home, the whole thing was perfectly level, all the legs sitting perfectly on the table, etc. Now, the legs diagonally across from each other teeter back and forth, about 2mm from the surface of the table.

Oh, that is quite unfortunate... We knew the heat and humidity here in Augusta might be an issue, but we hadn't realized quite how much! You can feel the moisture in the air, it's crazy. We had prepared for this situation by bringing some special 'drying' materials to place in our boxes, but I'd thought about what we'd likely do if we ran into this situation. It seems to me that re-sanding to create a level surface would create an imbalance, as Balsaman stated previously. Since it's basically impossible to determine exactly where the humidity has affected the wood, to me, at least, I think it would be best just to make sure the feet are placed evenly on the testing platform before putting the loading block on. Without knowledge of the point that your 'transformed' bridge will be truly even, I don't believe it would make a whole lot of sense to sand down legs that might simply make it more unbalanced. Just my opinion...

[Greg Doe]

Aia,
Don't sand down the longer legs. The extra moisture shouldn't hurt. In fact it might help. See a previous post about moisture content on structural wood. Also note that there is a specification for moisture content in AIRCRAFT Wood. That Speck is probably below Georgia humidity! Hopefully not detritmental to SO Elevated Bridges.
Try the following to straighten. Place 1 mm pieces of wood under the feet that are TOUCHING
the table. Place a load on the bridge sufficient to make all the feet contact the table. Shouldn't take as much as a pound. Now take a hair dryer and warm the whole bridge for about 5 minutes. Let the
bridge cool, and then check it for twist. If it's twisted too much, back up the process. If it didn't go fare enough, do it again. Hair dryers are cool enough to not burn skin, so it shouldn't hurt the wood or glue. If the hair dryer doesn't do the job, step up to a Monokote Heat Gun, used to shrink the
plastic covering on model airplanes. Try to store your bridge in as dry a container as possible, with
some kind of moisture absorbant material inside. We used this process several times on regional and state winning bridges. Those bridges were built with carpenters wood glue, and super glue. Good luck, and if you get this message in time, let me know how you did.
Greg Doe
Smyrna, TN

[sewforlife]

YAY! Elevated Bridge is on the live webcam right now. http://www.wfxg.com/Global/category.asp?C=162634

[Aia]

YES!!!

Omg, I just had my best Elevated Bridge score ever! My bridge held the whole weight despite the huge mass gain from the humidity! YAY!

My score ended up being 1517- I had a 9.89g bridge (was 9.6g back in Seattle) and it held the full 15kg. I can't even tell you how happy I am! After fretting over the humidity-induced torque and mass gain, I was 100% sure that I would only hit 10kg or so. Quite frankly, I thought 1000 would be the best I could possibly get. I was the second to last bridge to load, and all day I was watching bridges snap. Many of the competitors walked out crestfallen, complaining that the humidity had increased their mass and decreased their strength (most people thought their scores were reduced by 200pts or so). I was so ready for mine to break... my bridge didn't even budge. : D : D : D

All told, I never did try to compensate for the new torque on the bridge- major thank you for the replies. I probably won't medal, but should hopefully get top ten or so.

But still, after an unfortunate state bridge and countless hours spent building, I am so thrilled to have hit my best. My SO career ends beautifully. : )

I'll report more about the scores later. I think I saw the top five bridges load for C- no 2000s (likely because of humidity), but multiple in the 1700-1900 range. I wasn't paying as much attention to B division scores, but there were some good ones.

[croman74]

YES!!!

Omg, I just had my best Elevated Bridge score ever! My bridge held the whole weight despite the huge mass gain from the humidity! YAY!

My score ended up being 1517- I had a 9.89g bridge (was 9.6g back in Seattle) and it held the full 15kg. I can't even tell you how happy I am! After fretting over the humidity-induced torque and mass gain, I was 100% sure that I would only hit 10kg or so. Quite frankly, I thought 1000 would be the best I could possibly get. I was the second to last bridge to load, and all day I was watching bridges snap. Many of the competitors walked out crestfallen, complaining that the humidity had increased their mass and decreased their strength (most people thought their scores were reduced by 200pts or so). I was so ready for mine to break... my bridge didn't even budge. : D : D : D

All told, I never did try to compensate for the new torque on the bridge- major thank you for the replies. I probably won't medal, but should hopefully get top ten or so.

But still, after an unfortunate state bridge and countless hours spent building, I am so thrilled to have hit my best. My SO career ends beautifully. : )

I'll report more about the scores later. I think I saw the top five bridges load for C- no 2000s (likely because of humidity), but multiple in the 1700-1900 range. I wasn't paying as much attention to B division scores, but there were some good ones.

Wow, congratulations! I'm glad you had success. Nice end to your career. Good luck to your team!

[dholdgreve]

OK, You are all welcome to give me a big, fat "I TOLD YOU SO!" after Nats, but my prediction is that Division B will be no higher than 1500 and Division C, no higher than 1800. This is totally different than Boomilever, with entirely different dynamics. Why you guys are even comparing efficiencies with that of Boom is beyond me... You may as well compare scores to Scrambler!

If ANYONE has PERSONALLY seen and documented a bridge in either Division that has scored more than either of those scores, I'd certainly like to hear about it... Second hand info doesn't count... Did you personally see it?

OK, So how does my original prediction compare to the high scores at Nationals? Inquiring mind want to know!

[quickestwinne]

top one for C was about 2400 and top one for b was about 2100.

I have seen the top one for C. It's at my house. The one that got 2nd in B is also there-it got around 2000.

[dholdgreve]

OK, So I'll still eat the crow... just not the feathers. You guys all thought I was whacked, thinking that C would out-perform B, but it looks like experience triumphed over the more difficult challenge posed to C after all!

Those are truly amazing scores. My sincerest congratulations to the winners as well as anyone or any team that made it to nationals. After 10 years in this program, I still somehow manage to under estimate your capabilities!

[Balsa Man]

YES!!!

Omg, I just had my best Elevated Bridge score ever! My bridge held the whole weight despite the huge mass gain from the humidity! YAY!

Aia, that great to hear- well done, sir! That must have felt great as the last couple kilos of sand went in. 1500+ is a serious accomplishment w/ this year’s specs (B & C); heck, getting >1200.is really good (both a smart design and good execution needed)

top one for C was about 2400 and top one for b was about 2100.

I have seen the top one for C. It's at my house. The one that got 2nd in B is also there-it got around 2000.

Top scores are not a total surprise. As dholdgreve says, truely amazing; a handfull of folk DO seem to come up with the amazing every year. I’m really curious about how the scores came out for both C & B below the top 2 or 3– at least the top 10 or so. Hopefully someone can provide that insight (rjm?) - a little more complete picture of how the building skills vs geometry tradeoffs played out. Still guessing that B average in this range will be higher than C, but beginning to think I could well be be wrong. I really hope we’ll see some pictures posted to the Image Gallery of some of the successful designs.

A few observations from watching the webcast (realizing their selection may not have been representative of the field)-

It did seem like there were a lot of premature failures – like earlier than expected. High humidity, and the consequences of that certainly was a factor.

I was surprised at the number of arches – and am very curious if any made top 10. I and some others had the sense that there were real limitations on how competitive an arch could be.

Saw a few tip-over failures, which I assume were straight-sided configurations. My guess is that nobody with the sides leaned in a bit ran into that.

A few comments on the two bridges I was involved with – the Colorado ones; Poudre in C, Blevins in B; both being based on the design of my son’s State bridge. In both cases, very little time between State & Nats to build a new design. Poudre’s was essentially the same design, with laminated balsa legs replacing basswood ones (light core w/ angle iron 1/64th lamination) – got to watch it go on the webcast. Weighed in from the report I got at 9.85g, carried 12.59kg; 1304; 10th place. I think I know why it didn’t make it all the way to 15 (I’ll have to verify this with them when they get back) – it looked like there were no tension control strips at the bottom of the legs. With a 3/32nds lean-in on the sides, there is a slight separating force at the leg ends, not much, but enough to need a little piece joining/holding leg ends together.

Blevins’ was the same design modified to B dimensions, w/ the same laminated leg construction; weighed in at 7.50g, carried 9.63kg, 1284, don’t yet know placing. Their run wasn’t webcast, but got a live cell phone report. Failure appeared to be where we expected; lower leg section. Because of the higher bottom clearance required in B, the exposed column lengths in the legs were longer than in the C bridge. Calculated load it should have carried (from my son’s bridge) was about 90% of what it would have seen at 15kg loading. That we had a leg failure around 50%, probably a combination of variation in wood and glueing of laminations, and humidity. With higher density wood seeing a greater dimensional change than lighter wood, the laminated leg construction + humidity may well have meant a slight curve instead of being straight.

Congratulations to all that did well; the winners, the medalists, those that came close. Looking forward to hearing more on exactly what happened at Nats, and how the rules will be tweaked for next year.........

[croman74]

top one for C was about 2400 and top one for b was about 2100.

I have seen the top one for C. It's at my house. The one that got 2nd in B is also there-it got around 2000.

I'm guessing that you were the coach of those two teams. Congrats to the top bridges. Impressive scores from both divisions.