## Testing Apparatus

zcshiner
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### Testing Apparatus

My coach and I have a question. He usually runs the Elevated Bridge or (this year) Towers event at our regional competition. We have a concern with Rule # 5.h The load held must be measured in kilograms to the nearest gram.

Does anyone know where to get a balance or scale that can measure up to 15.2Kg and is accurate to the gram? So far, we are unable to find one that is that accurate, with such a range.

Thanks.

SLM
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### Re: Testing Apparatus

zcshiner wrote:My coach and I have a question. He usually runs the Elevated Bridge or (this year) Towers event at our regional competition. We have a concern with Rule # 5.h The load held must be measured in kilograms to the nearest gram.

Does anyone know where to get a balance or scale that can measure up to 15.2Kg and is accurate to the gram? So far, we are unable to find one that is that accurate, with such a range.

Thanks.
Here is one, though a bit pricey: http://www.discountscales.com/andgxk-series.htm

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### Re: Testing Apparatus

If you can get a bathroom scale that is accurate to 3 decimal places (since weight is usually in kg), that might work as well.

I'm not exactly sure where to get one, though.
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blue cobra
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### Re: Testing Apparatus

It seems those scales are very expensive. If that's in your budget, go ahead. Otherwise, ask around other schools in your region to see if they have one you can borrow for the competition.

Just in case you absolutely can not get an appropriate scale, and you really should try everything to do that, I'd suppose the best thing to do would be to use the best scale you can (which is...?) and get a clarification for your region at least 30 days before the competition that you will be using that scale. Really try to get the right scale though. Even at the regional level, it's important to run events within the parameters of the rules.
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smartkid222
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### Re: Testing Apparatus

Just try to find the most precise one you can afford. I wouldn't fret it. If you could find something that is +/- 10 grams that's really fine. Most regionals measure the weight of the tower to a tenth of a gram (example: 7.7g) instead of to a hundreth and i think that has a greater affect than a difference of something like 14.444kg and 14.44kg on the large scale.
disclaimer: i didn't do the math to back this up
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old
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### Re: Testing Apparatus

You are going to have a heck of a time finding a reasonably priced scale that can measure 15+KG to within a gram. The one we have used for years in our region can read to 5 grams, and we have never even come close to having a tie. This year with the loading mass being squared it does make the measurement more significant (is this really true?) but I am expecting that many of the towers this year will survive, so they will just get the full 15KG. If it is true that many towers survive, then measuring the mass of the tower becomes more critical. If you only weigh the towers to 0.1 gram rather than 0.01, then a tie become more probable.

old
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### Re: Testing Apparatus

I forgot to mention, for the question that is more important to the builders, a testing apparatus that you can use to see how well your tower is doing, I have some ideas. One of the big problems when testing these structures with a simple bucket of sand is that the tower breaks so fast that even with a video camera it is nearly impossible to pinpoint the actual break point. When the first piece breaks the bucket falls and tends to tear up the structure so much that you often cannot find out what actually caused the failure. What we did to deal with this was to build a simple device that allowed us to load the structure with a press and measure how much force we were putting on it. Since nothing was free falling we could stop the destructing immediately upon the first failure, and then see what was actually breaking. Sometimes we could actually save the entire structure and just reinforce the site of the first break point.

This same device is also useful for testing portions of the structure or even individual pieces of wood. You can load them to the point where they buckle, but not allow them to go so far that they actually break. Every time I think of how much work this all was I shudder at the prospect of building another SO structure, ugh! You can got the cross your fingers or pray to God, Allah, etc. route, and save a ton of time, but that method never worked well for me.

blue cobra
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### Re: Testing Apparatus

old wrote:<SNIP>One of the big problems when testing these structures with a simple bucket of sand is that the tower breaks so fast that even with a video camera it is nearly impossible to pinpoint the actual break point. When the first piece breaks the bucket falls and tends to tear up the structure so much that you often cannot find out what actually caused the failure. What we did to deal with this was to build a simple device that allowed us to load the structure with a press and measure how much force we were putting on it.<SNIP>
Or, if you don't have a press, you can build a safety tower. It doesn't take long to build and can be built with materials you probably already have.

1048|39/P3240147Safety_Tower.jpg
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SLM
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### Re: Testing Apparatus

SLM wrote:
zcshiner wrote:My coach and I have a question. He usually runs the Elevated Bridge or (this year) Towers event at our regional competition. We have a concern with Rule # 5.h The load held must be measured in kilograms to the nearest gram.

Does anyone know where to get a balance or scale that can measure up to 15.2Kg and is accurate to the gram? So far, we are unable to find one that is that accurate, with such a range.

Thanks.
Here is one, though a bit pricey: http://www.discountscales.com/andgxk-series.htm
Here is a much cheaper scale with 30 kg capacity and 1 gram resolution.

http://www.scalesusa.zoovy.com/product/ ... g=DW-94CAM

andrewwski
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Yes, the error will be more significant. Consider an error $\sigma_l$ for load. Score is calculated as $s=\frac{l^2}{w}$ for s=score, l=load, m=mass of structure, thus $\sigma_s=\frac{ds}{dl}\sigma_l=2dl$. Similarly, consider the error in weight of the structure, in which you get $\sigma_s=\frac{ds}{dm}\sigma_w=dm$. So the error in measurement of the load would be twice as significant.