Elevated Bridge B/C

andrewwski
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Re: Elevated Bridge B/C

Postby andrewwski » September 7th, 2009, 6:32 pm

Sand. Went through my first year of Boomilever using whatever I could find - sand, marbles, 1 gram weights, etc, and it was a huge pain. Plus spending the time switching between different sources made the bridge support the weight that much longer. You should be able to get more than enough sand for $5 at a hardware store.

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Re: Elevated Bridge B/C

Postby Cyrus_D » September 7th, 2009, 6:50 pm

Thanks. And do you guys use chairs or have like a platform to test it with?

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Re: Elevated Bridge B/C

Postby robotman » September 7th, 2009, 6:57 pm

my team uses a large piece of wood with the regulation hole cut in it and we set it between two tables
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Re: Elevated Bridge B/C

Postby Cyrus_D » September 7th, 2009, 7:15 pm

I thought that rules stated the testing platform needed to be slick? Did it not?. I use our science tables at school, which are relativity slick.

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Re: Elevated Bridge B/C

Postby nejanimb » September 7th, 2009, 7:33 pm

It does say it should be slick-ish, but it doesn't have to be that slick - it really depends on the competition. We have a platform which is pretty much the same as what they use at competitions - not sure what the material is though. It was made, I think, for towers, so it's self-contained - no gap is actually "bridged". The table works for towers, booms, and bridges, which is neat.
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Re: Elevated Bridge B/C

Postby rjm » September 7th, 2009, 8:43 pm

The rules say that the Test Base "shall have a smooth, hard surface". No statement is made about the friction coefficient of the surface, so you need to design for a worst case. You must assume that there will be no useful resistance to slipping between the test surface and the bridge. That generally means that the bridge has to be stiff enough that the ends don't slide outward (or any direction) while the bridge is being loaded, or if the ends do slide, the bridge can still function. The actual test surface could have a high friction coefficient, but you can't count on it, and you can't appeal a test surface which is more slippery than you'd expected.

Several years ago we used a Towers test base made of formica-covered particle board, and we had a competitor who brought in a tower with no horizontal bottom struts to tie the bottoms of the legs together. The legs promptly slid outward and literally unzipped the diagonal bracing on the sides of the tower. The competitor complained that this never happened on the plywood test base that he used at his school, and the test base we used was too slippery. His appeal was denied, but the lesson is that you can't make assumptions about the competition which aren't stated in the rules.

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Re: Elevated Bridge B/C

Postby robotman » September 8th, 2009, 3:57 am

I thought that rules stated the testing platform needed to be slick? Did it not?. I use our science tables at school, which are relativity slick.
oh i forgot to add that the wood we is a counter top type laminate so it is fairly slick
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Re: Elevated Bridge B/C

Postby T-B » September 11th, 2009, 9:10 am

The 2010 guidelines are out. The clearance under the bridge is more than doubled in Division B (15cm x 15cm new vs. 10cm x 10cm old), overall height limit is raised from 15cm to 20cm, and the limitation on individual member cross-section is removed. Same structural efficiency ratio and weight limit (15kg). Let the building begin! :D

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Re: Elevated Bridge B/C

Postby andrewwski » September 11th, 2009, 12:08 pm

How about C?

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Re: Elevated Bridge B/C

Postby smartkid222 » September 11th, 2009, 12:37 pm

The 2010 guidelines are out. The clearance under the bridge is more than doubled in Division B (15cm x 15cm new vs. 10cm x 10cm old), overall height limit is raised from 15cm to 20cm, and the limitation on individual member cross-section is removed. Same structural efficiency ratio and weight limit (15kg). Let the building begin! :D
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