Wood Orders

Balsa Man
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Re: Wood Orders

Postby Balsa Man » Thu Aug 31, 2017 7:05 pm

Crtomir wrote:
Bob Miller wrote:Hey, so Specialized Balsa is a little slow when it comes to ordering decent wood, by a little i mean they were three weeks late with their estimated arrival time..... Any other decent balsa ordering websites that is quicker than Specialized? Also, what wood do you usually order and use on your towers?


I placed three separate orders to Specialized Balsa last year and they all came within a week or so and wood was of good quality and all pieces were within the density range I selected. I highly recommend them.


Having the luxury of being able to drive down to Specialized to pick orders up, can't comment on shipping timing. I do know Jake at Specialized work really hard to do timely shipping.

If there's any other place that allows you to order to a specified density (e.g., 1/8" sticks in 0.1gr increments for 36" sticks), I haven't heard of it,

That's critical for high performance. To maximize score, you want to get to a set of sticks/legs that are just barely strong enough. If you order/get enough sticks in a wider density range (like "medium"), the variation will get you a few that ....are what you really are looking for. Same situation if you buy sheets and cut/strip your pieces. You can order sheets in a narrow density/weight range from Specialized.

And the last thing to remember is, to get maximum structural efficiency, it is not the density, but the strength (buckling strength) that matters- see the graph in my post above. Buckling strength IS related to density, but there is significant variation around the mean. You can, for instance, have .....a bunch of, let's say 1.4gr/36" and 1.5gr/36" 1/8" sticks, and have a very significant difference in buckling strength, where the BS of some of the 1.4s is higher than some of the 1.5s. What you're looking for is a reasonably well matched (in BS) set, where the BSs are just above your design BS- the very lightest ones that meet design BS. It is wood selection based on required BS that will separate the really high performing towers from the....rest of the pack. So, being able to order to a tight density spec means you will have to order/work through fewer sticks to find the lightest, strong enough pieces you want.
Len Joeris
Fort Collins, CO

cool hand luke
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Re: Wood Orders

Postby cool hand luke » Fri Sep 01, 2017 10:53 pm

Balsa Man wrote:
cool hand luke wrote:
Balsa Man wrote: This year, I’ve shared the data I’ve developed on (1/8”) stick weights vs buckling strength here on Scioly- .



Does anyone know where this is? I found it last year but now I cant find it.


Let's see if thus works-
here it is via Google docs link
https://drive.google.com/file/d/0B60c_z-M8r5cZWRvNGNXWTVoVGc/view?usp=sharing

This a plot showing (bottom, blue line) buckling strength measured at 36", using 'single finger push-down" (which is under 'pinned-pinned' end conditions). The red and green lines above apply an effective length factor ("FE"). As discussed last year, if you use a ladders and Xs bracing configuration (which creates "fixed-fixed" end conditions for the braced leg segments between bracing points), FE at 2.3 applies (the red, upper line). When I say "applies", I mean it correctly predicts "in-place" leg buckling strength. Say you measure BS at 36" (91.6cm) at 40gr. 2.3 x 40= 92gr. Say you're looking at a C tower leg, at 61.34cm length, and you brace at 1/5 interval (which would mean a braced segment length of 12.27cm. 12.27 is 0.134 of 91.6. 1 over the proportion squared (1 over 0.134 squared) is 55.74. The braced segment will have a BS 55.74 times the BS (single finger push-down at 91.6cm times 2.3- 92gr), which = 5128gr, which is well over the needed buckling strength of 4572gr; it would give you a safety factor of about 12%.

As also discussed, FE for an "all Xs" bracing config is very different, and I'm still working on understanding... what it is, and why (from a theory basis) it is. I know from results on our Nationals builds it is around 0.4, I'll be doing.... more work to try to get it figured out, and will share when I get a handle on it.



I was following, but I'm very lost at a fe of .4 for the x's only build. can you help me understand?

Balsa Man
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Re: Wood Orders

Postby Balsa Man » Sun Sep 03, 2017 3:28 pm

Wish I could at this stage; as I said, I'm working on figuring it out, and I look forward to sharing when I do. The 'around 0.4' value is simply from what worked on our Nationals all Xs towers.
Len Joeris
Fort Collins, CO


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