Testing Apparatus

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Bubba1960
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Re: Testing Apparatus

Post by Bubba1960 » October 17th, 2010, 3:41 pm

200 - 2000 bucks? Im not ready to spend that kind of money.
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blue cobra
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Re: Testing Apparatus

Post by blue cobra » October 17th, 2010, 5:55 pm

Bubba1960 wrote:200 - 2000 bucks? Im not ready to spend that kind of money.
You don't have to. An appropriate scale for this event can be had for $10.68 with a calibration weight for $3.99. That's what I have and it seems to work well. The really expensive ones here measure at least 15kg x 0.001kg, which is just needed by the school running the event.
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Re: Testing Apparatus

Post by Balsa Man » December 11th, 2010, 7:23 am

blue cobra wrote:
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
Thought it might be helpful to bump a post some may not have looked at. A number of posts recently about building/testing lots of towers, one about using video to figure out what broke.
My experience is that video may catch the initial failure in a way you can tell what happened.....maybe one out of 10; more like one out of 20+ times. The exposure time for each frame is on the order of 1/3oth of a second. In a structure under significant load - say 12+ kg, things happen fast at failure; pieces move a lot in 1/30th second.

Building lots of towers, and breaking them, unless you know what broke (and- see other post about jigs today - unless they are the same shape/configuration) is essentially a waste of time. The only way you can really "develop", as in improve, a design is to a) increase the strength (weight) of pieces that are too light/weak, and decrease the strength of pieces that are too strong/heavy- you need to figure out which is which. The safety tower lets you do that. Blue Cobra pulled the picture from our 2009 bridge pictures- we've been using it since 2004- as pictured, it is big enough for towers. You can dig back into Bridge posts from last year for more detail on how it works. Basically, you set the top chain so that the load block can only drop like 1/8th inch; enough to allow initial failure, but not far enough to allow.....secondary damage/failures to take place. If you're lucky, in a tower, initial failure is in the bracing- ladder or X (or Z) diagonal bracing, and the legs don't break. If so, you can, with that tower, beef up the bracing (gluing/laminating pieces on what you have), and re-test to see if the legs are strong enough for full load...
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MrsKingCMS
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Re: Testing Apparatus

Post by MrsKingCMS » January 19th, 2011, 3:41 pm

When looking at the rules, it mentions that a 8 cm diameter circular opening is required above 30.0 cm of Division B tower. How is a 5 cm x 5 cm block going to be supported by an 8 cm diameter hole?

Please clarify...

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smartkid222
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Re: Testing Apparatus

Post by smartkid222 » January 19th, 2011, 3:45 pm

The tower must fit inside the 8 cm circular opening.
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soccerkid812
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Re: Testing Apparatus

Post by soccerkid812 » January 19th, 2011, 3:45 pm

MrsKingCMS wrote:When looking at the rules, it mentions that a 8 cm diameter circular opening is required above 30.0 cm of Division B tower. How is a 5 cm x 5 cm block going to be supported by an 8 cm diameter hole?

Please clarify...
the testing block that sits on top of the tower is a 5x5 block

above 30cm for division C, the tower must fit INSIDE a 8cm diameter circle, its an imaginary circle

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eta150
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Re: Testing Apparatus

Post by eta150 » January 20th, 2011, 6:36 am

soccerkid812 wrote:
MrsKingCMS wrote:When looking at the rules, it mentions that a 8 cm diameter circular opening is required above 30.0 cm of Division B tower. How is a 5 cm x 5 cm block going to be supported by an 8 cm diameter hole?

Please clarify...
the testing block that sits on top of the tower is a 5x5 block

above 30cm for division C, the tower must fit INSIDE a 8cm diameter circle, its an imaginary circle
Are you sure it's not under 35? Or are you talking about div. B?
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Re: Testing Apparatus

Post by soccerkid812 » January 20th, 2011, 11:41 am

eta150 wrote:
soccerkid812 wrote:
MrsKingCMS wrote:When looking at the rules, it mentions that a 8 cm diameter circular opening is required above 30.0 cm of Division B tower. How is a 5 cm x 5 cm block going to be supported by an 8 cm diameter hole?

Please clarify...
the testing block that sits on top of the tower is a 5x5 block

above 30cm for division C, the tower must fit INSIDE a 8cm diameter circle, its an imaginary circle
Are you sure it's not under 35? Or are you talking about div. B?
oh yea, ur right, my fault

division C: base of 15cm, 35cm chimney
division B: base of 30cm, 20cm chimney
50cm min for both towers

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deezee
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Re: Testing Apparatus

Post by deezee » February 2nd, 2011, 10:07 am

above 30 cm of the tower, the supervisors will probably place a tube with a diameter of 8 cm over your tower. the loading block is 5x5, but you can make the tower up to 5.6x5.6 cm
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Re: Testing Apparatus

Post by soccerkid812 » February 28th, 2011, 3:22 pm

i build my towers in 2 parts, the base and the top
when testing it, would each part have to hold all 15kg, or would the weight be distributed, for example, 7.5 in the top, 7.5 at the bottom?

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