Boomilever B/C

[sjwon3789]

I heard Aia used 3/16" as the compression members. Does anyone know if Aia used bass? Because I always use 3/16" balsa and it just breaks, as mentioned in earlier discussion. If it was bass, then would 1/8" balsa be recommended or 3/16" bass?

[UQOnyx]

No, its using the methods on the wiki. Lol mine is 2.5 grams just to be on the safe side...

[iwonder]

No, not using Aia's method for the base.

[Balsa Man]

The bracing can be hard to model, my theory is that you should just try it and find out, but .3g is in the range of stuff I've been using and it works fine

Indeed, truely modeling is hard. If you go back into discussion of bracing systems/configurations from towers and bridges, you'll see a number of opinions and analyses. No absolute resolution on "the best way." Xs, Z-bracing, and Xs & ladders were the types discussed. Very briefly, the purpose of this bracing- what it needs to do is, in the X- plane, is hold the braced points in place; to prevent movement when buckling starts to occur, when the piece starts to bow either toward, or away from the braced point. If the bowing is toward the brace, the brace is put into compression loading; if the bowing is away, then the bracing is put into tension loading - it has to be able to handle both. The force onto/away from the bracing at first is very low; if/as buckling/bowing is allowed to happen, the force rapidly goes up.

The short answer to the question- will 1/16th at 0.3gr/36" stick "work" - is yes, it probably can. Basis for that- simply, what iwonder's saying; it works. The only caveat- assuming the configuration you're using is essentially the same as iwonder's.

Figuring out its approximate buckling strength, though, is easy- as discussed a number of times, its inversely proportional to its length.
So, with a 36" stick (I presume), you've found the buckling strength at a bit less than 3 gr. For easy/even numbers, let's say 36" = 90cm.
Assuming you're using a 5cm separation between compression members, let's also assume you're using a 5cm bracing interval- 8 sets of Xs for a 40cm compression member length. That means the length of the X pieces is about 7cm. 7cm is approximately 1/13th of 90cm. 13 squared is 169. So if the buckling strength at 90cm is 2 gr, at 7cm its 169 times that = 338gr. If the buckling strength at 90cm is 3gr, then at 7cm, its 507gr. Those strengths are reasonably in the range to resist initial buckling. If your braced interval is different, easy to recalculate this way.

You can easily get a feel on tensile strength by simply taking a piece, glueing it to two "holding" pieces - something to hang onto, and pulling. My sense/experience is that for 0.3gr/36" 1/16th, it's less than the buckling #s, but again, at the start of buckling, it doesn't take much.

by sjwon3789 on Sat Mar 09, 2013 12:10 am I heard Aia used 3/16" as the compression members. Does anyone know if Aia used bass? Because I always use 3/16" balsa and it just breaks, as mentioned in earlier discussion. If it was bass, then would 1/8" balsa be recommended or 3/16" bass

I'm sorry, I'm having trouble making sense of what you're saying/asking. "If it was bass" that Aia used, then, obviously, it worked, and if you're looking for something that works/has worked for others, there you are. Unless you are using pretty high density balsa (for those 3/16ths members that aren't working), going to 3/16ths bass will give you higher buckling strength. I haven't taken the time to check back, but I don't believe Aia was using 3/16th bass.

When you ask if 1/8th balsa would work/be recommended, you really loose me. If 3/16ths balsa isn't working for you, going down to 1/8 balsa - which will be a lot weaker (about 1/3 less), certainly is not going to "work"- you'll be going in the wrong direction. If 3/16ths bass does work, going to 1/8th balsa would be a LOT weaker.....

[mrburrito]

My boomilever uses special wood, and my philosophy of how to build it is different than everyone else's in the nation. I know it sounds unbelievable, but it's true.

[Balsa Man]

Last time I checked, Hogwarts had not set up a Tennessee branch.
This is Science-O, not magic-O. Someone might share your real score at last competition.....

[UQOnyx]

lol this is hilarious. I happen to love trolls.

[_HenryHscioly_]

for tower-on-the-side design

is it better to attach tension members to the bottom two legs right under where the bolt will be, since if they connected to the top legs I would essentially be decreasing the height?

At high loads, I want all four legs to be in good contact with the wall, which means, at first, only the top two legs will be contacting the wall, if I angle the compression-tower a bit up
but, the tension members are connected to the bottom two legs...so, will this not work properly...?
or do I just need to have some big, stronger pieces near the distal end connecting the bottom and top legs..anyone have success with tower design?

[Balsa Man]

Good questions and good identification of issues.
Be very interested to see if anyone who has figured this approach out wants to talk about it.
When we were working through basic design options at the beginning of the season, saw more issues than advantages.
Which is why we went a different direction....

Haven't analyzed it closely. It would seem some plates/block combination at the distal end would be needed to tie the legs together, and tie in tension member(s), to get the load evenly distributed to all legs.

[sjwon3789]

by sjwon3789 on Sat Mar 09, 2013 12:10 am I heard Aia used 3/16" as the compression members. Does anyone know if Aia used bass? Because I always use 3/16" balsa and it just breaks, as mentioned in earlier discussion. If it was bass, then would 1/8" balsa be recommended or 3/16" bass

I'm sorry, I'm having trouble making sense of what you're saying/asking. "If it was bass" that Aia used, then, obviously, it worked, and if you're looking for something that works/has worked for others, there you are. Unless you are using pretty high density balsa (for those 3/16ths members that aren't working), going to 3/16ths bass will give you higher buckling strength. I haven't taken the time to check back, but I don't believe Aia was using 3/16th bass.

When you ask if 1/8th balsa would work/be recommended, you really loose me. If 3/16ths balsa isn't working for you, going down to 1/8 balsa - which will be a lot weaker (about 1/3 less), certainly is not going to "work"- you'll be going in the wrong direction. If 3/16ths bass does work, going to 1/8th balsa would be a LOT weaker.....

Oops, I said the wrong numbers and I thought of the wrong wood. I think I know which wood to select.