Elevated Bridge B/C

[smartkid222]

. anyways just let me know what you think it will get. woever is closest i will tell in private some secrets and techniques to it. P.S. there are some key pieces i left off when showing you guys so you cant just copy it

Ill say 13.75kgs for the heck of it. It really all depends on these "key pieces.

[Balsa Man]

Well, back from Regionals (N. Colorado).

First, B Div vs C Div.
Based on this, I’m at least wondering about my assumption of significantly higher efficiencies possible in B. I still think that some really good design and building skills applied to the B specs could outscore even a well done C bridge, but, hey, even after a lot of years , you learn something new almost every day.

B top 5- 607.3 (24.7g @ 15kg), 571.7(26.1@15kg), 485.2 (29g@14.07), 441.0, and 408.5
C top 5 1013.5 (14.8g @15kg), 826.9(12.4g @10.2K), 488.4 (24.5g @11.96kg), 477.7 (31.4g @ 15kg), and 471.8.

I’ll be very interested to hear what dholdgreve reports.

Ours (C-Div) weighed in at 14.8; we thought it would carry full load; it did without really breathing hard; some testing with a safety tower next week to see what it’ll really do, and where first failure mode will come from. Ver 2.0 should see testing soon, too; it’s a few grams lighter. There were 3 other bridges <14.8 gr; the lightest at 10.4, but the highest they scored was 402.9

It was a fun day

Len Joeris
Fort Collins, CO

[Pleiades]

That really surprises me. Those B bridges look awfully heavy. Did they look overbuilt?

[Balsa Man]

Yeah, almost all of them did; relatively large x-section wood, bracing where it really didn't need to be. There were a couple with decent weights, that looked well conceived and executed, but they just didn't carry much load. Technique is clearly a factor; it takes time to get the skills, and learn a few tricks.

From both my boys' Jr Hi days, my sense of the B field was there were some folk who had worked hard, who had put at least some good thought into design- who understood some basics - and my hat's off to them, but nobody who.....is on the path to National -level competitiveness.

Len Joeris
Fort Collins, CO

[andrewwski]

No doubt they were overbuilt. Looking at B specs there's no way 24+ g of balsa is necessary. And since the top two held the full 15, chances are they could hold more, which means they were overbuilt. Don't even need to see the bridges - the numbers say it all.

[frontlineballer1]

For those of you that were wondering my bridge that i once had a picture of it up weighed in at about 8.2 grams. and it usually holds just over 13 kg. unfortunately for my competition i was in the last time black and it was in a very humid room so it picked up a lot of weight. just about .8 grams. it consisted of almost entirely basswood except the legs were 1/8" balsa. Also the legs were exactly how they were on my final bridge so yeah all your speculations were innaccurate. In fact i made this little test base were i attached the legs to a solid block of Oak. and set it up to load just to test how much the legs could hold. I filled up my 5 gallon bucket with water and it didnt fail. this is about 50lb of water. (i didnt have enough sand to break them). that just goes to show how amazing balsa can be in compression.
just to let you all know the person that was closest PM'ed me with almost exact specs. and also the mode of failure is the compression member (generally)

I would've liked to experiment more with some balsa in the design but i had other events to worry about so i didnt have as much time and focus as i wouldve liked for this event.
cheers.

[Aia]

Back from Regionals:

The scores were extremely split for C division- The 3rd and 4th place teams were only 50pts apart, but they were separated from the 1st and 2nd place scores by >1000pts. I believe all the other bridges were second tiered for some reason or another, but their efficiencies still were only as high as 500 or so.

The scores were much closer for B divison: The top three places were between 1000 and 1100, and the designs were all almost identical (but these were different schools).

It'll be interesting to see how state goes... I'm guessing the gap in the C division scores won't be as large.

[Flavorflav]

More than 1000 points? Seriously? What was the winning efficiency?

[Allirog24]

Thanks for saying what the efficiencies of the bridges are, that makes me feel a lot better!

[Balsa Man]

So, Aia, how'd you do?

Len Joeris
Fort Collins, CO