Towers B/C

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hearthstone224
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Re: Towers B/C

Post by hearthstone224 »

Hey BannanaPirate, welcome!

You may not be getting as high of a BS as you think you should because maybe you are doing the testing differently than we are. I test the sticks until the number on the scale stays fairly the same. So if I'm pushing it down and I see that the numbers are staying in one place, I count that number regardless of how far I'm pushing it (as long as it isn't going to break).

So try that approach. I'm not sure how far out you are pushing it, maybe you should go a bit further.
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Re: Towers B/C

Post by Balsa Man »

HandsFreeCookieDunk wrote:
BananaPirate wrote:
Balsa Man wrote:
Yup, these are buckling strength at 36". You should see about that buckling strength in 1/8 x 1/8 at about 1.5gr (36") stick weight. 1.4 at about 75.. 1.6 at about 85gr. What can I say, that's what our testing's seeing.....

Len Joeris
Ft. Collins CO
That's interesting...just to confirm, you are pushing down on a scale until around a 0.5 cm bow? Perhaps my sample size is too small, I will do some more testing as well. The only other thing I can think of is that the balsa sticks I am testing with (from Menards and Hobbytown), are lower quality than ones bought from another retailer like specialized balsa. This may result in same density but different buckling strength? Thanks for the quick response!
It is very likely that your sample size is too small. In general, cheaper, lower quality balsa is lower quality not because its weaker, but because there is far more variability in strength and density.
There are a number of factors that could be at work here.
First is if there's any bow in the sticks. If there is (and it doesn't take much), tested buckling strength will be significantly low; essentially it's already buckling when you start. You want to get a reading for buckling toward each of the four faces; when pushing down with one hand, use a finger of the other hand, pushing gently at the middle to push/induce bowing in all 4 directions; average results.
Second, which could be a wood 'quality' issue; soft spots/zones, somewhere along the stick there's a stretch where density is significantly lower than overall density of the stick. You can feel such zones by holding the stick at one end and running two fingers along the length- one along the top side, one along the bottom- let's see, how to explain....looking at stick from the side, position top finger at 2 o:clock, underneath finger at 8 o:clock; rotate them both clockwise; just a bit. That'll bend the end of the stick downward. With that pressure on, slide both fingers out along the stick. The amount of bend should remain pretty constant. If you hit a soft spot, you'll feel it, and the amount of bend will increase noticeably.. If you see this, put that stick (or the weak section) in the scrap pile. Places like Specialized Balsa will ....generally weed out/not sell/ship 'junk wood' much more rigorously than places like Hobbytown/Menards.

And just a side note, if you order/buy from such suppliers, the variation in density is actually likely to be fairly low; in the 1.4 to around 2.1 "medium" density range, because its most common, and cheapest for them to buy......

Len Joeris
Ft Collins, CO
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Re: Towers B/C

Post by BananaPirate »

Balsa Man wrote:
HandsFreeCookieDunk wrote:
BananaPirate wrote: That's interesting...just to confirm, you are pushing down on a scale until around a 0.5 cm bow? Perhaps my sample size is too small, I will do some more testing as well. The only other thing I can think of is that the balsa sticks I am testing with (from Menards and Hobbytown), are lower quality than ones bought from another retailer like specialized balsa. This may result in same density but different buckling strength? Thanks for the quick response!
It is very likely that your sample size is too small. In general, cheaper, lower quality balsa is lower quality not because its weaker, but because there is far more variability in strength and density.
There are a number of factors that could be at work here.
First is if there's any bow in the sticks. If there is (and it doesn't take much), tested buckling strength will be significantly low; essentially it's already buckling when you start. You want to get a reading for buckling toward each of the four faces; when pushing down with one hand, use a finger of the other hand, pushing gently at the middle to push/induce bowing in all 4 directions; average results.
Second, which could be a wood 'quality' issue; soft spots/zones, somewhere along the stick there's a stretch where density is significantly lower than overall density of the stick. You can feel such zones by holding the stick at one end and running two fingers along the length- one along the top side, one along the bottom- let's see, how to explain....looking at stick from the side, position top finger at 2 o:clock, underneath finger at 8 o:clock; rotate them both clockwise; just a bit. That'll bend the end of the stick downward. With that pressure on, slide both fingers out along the stick. The amount of bend should remain pretty constant. If you hit a soft spot, you'll feel it, and the amount of bend will increase noticeably.. If you see this, put that stick (or the weak section) in the scrap pile. Places like Specialized Balsa will ....generally weed out/not sell/ship 'junk wood' much more rigorously than places like Hobbytown/Menards.

And just a side note, if you order/buy from such suppliers, the variation in density is actually likely to be fairly low; in the 1.4 to around 2.1 "medium" density range, because its most common, and cheapest for them to buy......

Len Joeris
Ft Collins, CO
Hm ok so if I order from specialized balsa it seems like there will be a better chance for more accurate/complete results. Shame though, I was hoping I could finish off my density vs buckling strength graph before ordering from there. Thanks for the help guys!
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Re: Towers B/C

Post by Random Human »

BananaPirate wrote:
Balsa Man wrote:
HandsFreeCookieDunk wrote:
It is very likely that your sample size is too small. In general, cheaper, lower quality balsa is lower quality not because its weaker, but because there is far more variability in strength and density.
There are a number of factors that could be at work here.
First is if there's any bow in the sticks. If there is (and it doesn't take much), tested buckling strength will be significantly low; essentially it's already buckling when you start. You want to get a reading for buckling toward each of the four faces; when pushing down with one hand, use a finger of the other hand, pushing gently at the middle to push/induce bowing in all 4 directions; average results.
Second, which could be a wood 'quality' issue; soft spots/zones, somewhere along the stick there's a stretch where density is significantly lower than overall density of the stick. You can feel such zones by holding the stick at one end and running two fingers along the length- one along the top side, one along the bottom- let's see, how to explain....looking at stick from the side, position top finger at 2 o:clock, underneath finger at 8 o:clock; rotate them both clockwise; just a bit. That'll bend the end of the stick downward. With that pressure on, slide both fingers out along the stick. The amount of bend should remain pretty constant. If you hit a soft spot, you'll feel it, and the amount of bend will increase noticeably.. If you see this, put that stick (or the weak section) in the scrap pile. Places like Specialized Balsa will ....generally weed out/not sell/ship 'junk wood' much more rigorously than places like Hobbytown/Menards.

And just a side note, if you order/buy from such suppliers, the variation in density is actually likely to be fairly low; in the 1.4 to around 2.1 "medium" density range, because its most common, and cheapest for them to buy......

Len Joeris
Ft Collins, CO
Hm ok so if I order from specialized balsa it seems like there will be a better chance for more accurate/complete results. Shame though, I was hoping I could finish off my density vs buckling strength graph before ordering from there. Thanks for the help guys!
Specialized balsa is really good if you want to specify range, If you live far away from colorado(where specialized balsa headquaters are) then you should buy wood on a mass amount because the shipping is expensive. The downside of specialized balsa is you cannot handpick your sticks, but they should give you somewhere around what you are looking for.
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Re: Towers B/C

Post by Balsa Man »

You can specify stick weights, in 1/10gr increments, (e.g between 1.5 and 1.6gr), and that's what Jake will ship you
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Re: Towers B/C

Post by dholdgreve »

Balsa Man wrote:You can specify stick weights, in 1/10gr increments, (e.g between 1.5 and 1.6gr), and that's what Jake will ship you
Although the guys (and gals) at Specialized will gladly do this, it is very expensive to to do it this way. In addition, although I'm sure they will nail the requested weight, I don't know if they will do stiffness tests, so even after you get the weight sticks you want, they may not meet the stiffness expectations. I'd suggest that you consider buying sheets of the appropriate thickness, then, with the money you save, invest in a good balsa wood stripper. Strip all the material down, then figure out a system to analyze stiffness to weight ratios, and go from there.
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Re: Towers B/C

Post by Balsa Man »

dholdgreve wrote:Although the guys (and gals) at Specialized will gladly do this, it is very expensive to to do it this way. In addition, although I'm sure they will nail the requested weight, I don't know if they will do stiffness tests, so even after you get the weight sticks you want, they may not meet the stiffness expectations. I'd suggest that you consider buying sheets of the appropriate thickness, then, with the money you save, invest in a good balsa wood stripper. Strip all the material down, then figure out a system to analyze stiffness to weight ratios, and go from there.
Yup, that'll work, and save you some money - its a time vs money tradeoff. You're still going to need/want to target a density range for sheets ordered, so with sheet, you'll want to specify sheet weight (for 3"x36" x 1/8 sheet, to cut to 1/8 x 1/8, would be 24 x your target 1/8 stick weight.
And, yes, if you order/get a set of sticks around a target weight, some will turn out to have less than average stiffness, some show above average stiffness, with most around the average. What you're looking for for a 'competition build' is that set of the lightest, nice straight sticks (actually leg-length sections of sticks) that meet target/design stiffness. When you strip a sheet, you'll have most near target weight, some heavier, some lighter; and each of these categories will have stiffness variation, but again, selection for 'competition build' will be for the lightest that meet target stiffness (buckling strength).

Its the 'design (buckling) strength' you need for a leg/set of legs to 'work' (able to carry the force the leg will see at/near full load on the tower); the 'design' stick weight is a tool, a guide, an educated/calculated basis for ordering wood (if you don't have the luxury of being able to go to a place like Specialized and sort through a bunch of sticks by both weighing and doing initial 36" buckling strength testing). Either way, there is an element of cost inefficiency/waste built in (wood you buy and don't use), because of the natural variability that is inherent in wood - out of a larger set of sticks, finding the few 'optimal'/'best' ones.

Unfortunately, there's no easy/cheap/straightforward way around this, or if there is, I haven't been able to figure it out in 15+ years of learning/playing around/testing. The approach I've been discussing isn't perfect (and isn't the only way to approach the problem), but it will get you a lot farther than flying blind. This is, for want of better words, the....'dark art' at the heart of coming up with a seriously competitive wood structure. The more rigorously you apply/get into it, the bigger your chance of creating a "winner." I say 'chance', because you can't ever be certain how a given structure will perform- everything you can control/test/measure may be the same as a structure you tested that held full, or whatever load, and the new one....just doesn't....
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Re: Towers B/C

Post by sciolyrulz »

Hi!!
This is my first time doing Towers.
I am pretty confused about the word "span" in part 3a in the Towers rules, which says "The Tower must span a 20 cm x 20 cm opening on a test base and may be placed on the Test Base surface in any configuration.."
Does the tower base have to be completely outside the opening (A), or can it "overlap" the square opening in some parts (B)? In other words, does the 20 x 20 opening have to be completely clear? or can I have parts of my tower's base covering some of the edges?
I drew some diagrams to maybe help.
Thank you so much!!
https://docs.google.com/drawings/d/14Sg ... sp=sharing
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Re: Towers B/C

Post by Unome »

sciolyrulz wrote:Hi!!
This is my first time doing Towers.
I am pretty confused about the word "span" in part 3a in the Towers rules, which says "The Tower must span a 20 cm x 20 cm opening on a test base and may be placed on the Test Base surface in any configuration.."
Does the tower base have to be completely outside the opening (A), or can it "overlap" the square opening in some parts (B)? In other words, does the 20 x 20 opening have to be completely clear? or can I have parts of my tower's base covering some of the edges?
I drew some diagrams to maybe help.
Thank you so much!!
https://docs.google.com/drawings/d/14Sg ... sp=sharing
Design B would be legal so long as it doesn't go below the surface of the test base.
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Re: Towers B/C

Post by Balsa Man »

sciolyrulz wrote:Hi!!
This is my first time doing Towers.
I am pretty confused about the word "span" in part 3a in the Towers rules, which says "The Tower must span a 20 cm x 20 cm opening on a test base and may be placed on the Test Base surface in any configuration.."
Does the tower base have to be completely outside the opening (A), or can it "overlap" the square opening in some parts (B)? In other words, does the 20 x 20 opening have to be completely clear? or can I have parts of my tower's base covering some of the edges?
I drew some diagrams to maybe help.
Thank you so much!!
https://docs.google.com/drawings/d/14Sg ... sp=sharing
This was discussed in earlier posts
Your figure B is fine. "Span' simply means legs touch base outside. Also see thread on 29cm circle bonus.
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