Efficiencies

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iYOA
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Re: Efficiencies

Post by iYOA »

thanks

i know what you two mean. We ordered our wood from the same place twice. The first time, the wood was pretty heavy and that is why our towers were 9-10.5 but then the second order was really light so we reduced the weight by about 3-4 grams. There is a slight bit of luck involved i guess but maybe you can talk to the people and ask them to send lighter wood?
http://www.balsawoodinc.com/

EDIT: Actually, you can customize your order. This is what it says on the site.
"We can hand select balsa wood to suit your needs. Balsa wood sheets are available in Soft, Medium, and Hard. Hand selection is not the same as weighing the wood to determine its weight. Please include your specifications in your order details. 30% will be added to the base price of your order."
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Re: Efficiencies

Post by jander14indoor »

Even when you order specific weights, expect to sort AGAIN and still through out a lot of wood. Its just part of the normal variability of a natural product like balsa.

But, if you want to do really well, this is just a necessary part of the process. You can design the best structure, but unless you select the right materials its just junk.

Jeff Anderson
Livonia, MI
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Re: Efficiencies

Post by soccerkid812 »

jander14indoor wrote:Even when you order specific weights, expect to sort AGAIN and still through out a lot of wood. Its just part of the normal variability of a natural product like balsa.

But, if you want to do really well, this is just a necessary part of the process. You can design the best structure, but unless you select the right materials its just junk.

Jeff Anderson
Livonia, MI
If you do order light wood, how would you sort through them again?
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Re: Efficiencies

Post by lllazar »

IYoa, that site looks very nice for pricing, but how much shipping did u end up paying? Specialized balsa charged us like 17 bucks - our order itself cost 17 bucks.

Also, where do you specify that you want hand selected wood? I don't see anything for that anywhere.

Thanks!
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Re: Efficiencies

Post by dholdgreve »

bmbw123 wrote:I'm sure this is a relatively stupid/simple question, but is there a certain way you all pour in the sand. If a lever system is used to let the sand fall in, would you want to go slow, then faster, then switch back to slow? Letting the sand in slow seems like it would make your tower sustain the weight for longer times, but faster streams seems a bit all of a sudden.

And if there is a manual sand system, then I would assume you would try to pour the sand around the bucket evenly, so there are no mounds, and try to do it as quick as possible?
bmbw,
The age-old question... To level the bucket or not... The real challenge is to keep the bucket as still as possible. If the bucket leans one way or the other due to more sand being in one side than the other, that is fine... Do not try to level the sand in the bucket. The ojective here is to keep the chain as vertical and still as possible. By focusing on leveling the sand within the bucket, you will almost certianly lose focus on what is really important... Keeping the bucket from swaying, and keeping the chain still and straight. Even if the bucket hangs at a 45 degree angle, that's fine. With there being only one chain connecting the bucket to the loading block, all the load transfers through that chain. If there were two chains connecting the bucket to the tower, you would want to keep the bucket level, but with one chain it just doesn't matter where the swand is within the bucket, so long as the bucket isn't moving... What's it going to do? Pull harder on one side of the chain than the other?

As for the speed of which to add the sand, I think that is pretty much personal opinion... I agree that starting it with a thump is probably not a real good idea, and that a smooth, steady flow makes sense. I'd also suggest that with an automatic dispenser, you begin slowly, but quickly build to the maximum flow allowed by the device, and keep it pegged until the end... A couple of reasons... 1) As you mentioned, under a heavy load, a tower will only hold for so long... get as much in as possible during that time, and 2) Proctor's reaction time. If the automatic loader has a emergency shut off, it is probably triggered by an event proctor. i.e. as soon as the tower breaks, he pulls a disconnect, and a flapper or knife valve closes off the sand flow. Let's assume that this reaction time is .5 seconds. The reaction time would be the same whether the sand is flowing at full speed or barely flowing, but slightly more sand will flow into the bucket after the tower breaks if you are running it wide open.
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Re: Efficiencies

Post by jander14indoor »

soccerkid812 wrote:
jander14indoor wrote:Even when you order specific weights, expect to sort AGAIN and still through out a lot of wood. Its just part of the normal variability of a natural product like balsa.

But, if you want to do really well, this is just a necessary part of the process. You can design the best structure, but unless you select the right materials its just junk.

Jeff Anderson
Livonia, MI
If you do order light wood, how would you sort through them again?
The company is only going to sort wood to a general range, light, medium, heavy. You need a specific weight for your tower, you'll need to weigh each piece to ensure its density is correct for the intended use. In addition, weight is NOT the only parameter. Stiffness (see threads on construction and design) is as or more important. After selecting for correct weight/density, you need to compare how easy the pieces are to bend. Select matching stiff ones.

Jeff Anderson
Livonia, MI
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Re: Efficiencies

Post by iYOA »

lllazar wrote:IYoa, that site looks very nice for pricing, but how much shipping did u end up paying? Specialized balsa charged us like 17 bucks - our order itself cost 17 bucks.

Also, where do you specify that you want hand selected wood? I don't see anything for that anywhere.

Thanks!
Im not sure where to specify but they say here, under balsawood http://www.balsawoodinc.com/balsawoodproducts that they will hand select it. We have not asked for a hand selected order yet so we dont know how that would work.

Shipping costs about $12 and our order totaled to about $40 with the shipping.
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Re: Efficiencies

Post by soccerkid812 »

What size wood and wood densities are you guys using for the compression and tension members?
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Re: Efficiencies

Post by Arthur »

does anyone know the winning efficiency from the conestoga invite?
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Re: Efficiencies

Post by sj »

Arthur wrote:does anyone know the winning efficiency from the conestoga invite?
Yeah, I had a 9.7 gram tower that held all 15 kilos so a 23.1 efficiency. :D
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