Boomilever B/C

[Balsa Man]

Is there a way to calculate how many lateral bracings are needed?

Yes, to some extent, if you know the buckling strength of the members you're bracing.
The fuzziness around "to some extent" - the limits on how precise you can get what the buckling strength is- depend on a number of things. The two biggies are:
-the geometric precision you are working to; if you take a piece and put it under axial compression loading- the pushing/compression force exactly along its centerline, its axis, it will have some buckling strength. If the alignment of that force is off-axis, the measured buckling force will be less. It does not take much 'off-axisness' to reduce the buckling strength a lot. If the piecee is not perfectly straight, much lower buckling strength than a truely straight piece.
-the inherent variability of wood. Even if you have two pieces that are straight, and of the same density, and without apparent ....defects (soft areas, funky grain, etc), their buckling strength is not going to be the same. Sometimes, they can be pretty close, sometimes they can be significantly different; easily 10%, maybe 15%.

Back last season, in February, you asked pretty much the same question. and there was a lot of detailed information provided, and discussion around how buckling and bracing works. I'd suggest you (and anyone who hasn't developed a good understanding of these basics) go to last year's boom discussions and digest the information that's there.

[baker]

Some very good utilities for figuring wood density....
http://www.indoorduration.com/indoordur ... lities.htm

[UQOnyx]

Is there a way to calculate how many lateral bracings are needed?

Yes, to some extent, if you know the buckling strength of the members you're bracing.
The fuzziness around "to some extent" - the limits on how precise you can get what the buckling strength is- depend on a number of things. The two biggies are:
-the geometric precision you are working to; if you take a piece and put it under axial compression loading- the pushing/compression force exactly along its centerline, its axis, it will have some buckling strength. If the alignment of that force is off-axis, the measured buckling force will be less. It does not take much 'off-axisness' to reduce the buckling strength a lot. If the piecee is not perfectly straight, much lower buckling strength than a truely straight piece.
-the inherent variability of wood. Even if you have two pieces that are straight, and of the same density, and without apparent ....defects (soft areas, funky grain, etc), their buckling strength is not going to be the same. Sometimes, they can be pretty close, sometimes they can be significantly different; easily 10%, maybe 15%.

Back last season, in February, you asked pretty much the same question. and there was a lot of detailed information provided, and discussion around how buckling and bracing works. I'd suggest you (and anyone who hasn't developed a good understanding of these basics) go to last year's boom discussions and digest the information that's there.

thanks. I remember that much, but I wanted to know if there was a systematic way of doing it, like the way you can mathematically calculate bracing needed for compression.

[Balsa Man]

As I said, "Yes, to some extent, if you know the buckling strength of the members you're bracing."
The how that you're asking about is explained and discussed in detail where I pointed you to.

[technomario]

What type of wood do you recomend as a strong substitute to balsa wood?

[Balsa Man]

What type of wood do you recomend as a strong substitute to balsa wood?

Well, oak is a lot stronger than balsa......

OK, seriously-
What you're trying to do, in the overall structure, and in each of the pieces in it, is come up with the lightest that just barely carries the forces it's subject to at full load. It's all about structural efficiency.

In many cases, balsa gives you the highest structural efficiency. Bass is the most commonly used alternative to balsa, and there are definately places/situations where it is the higher efficiency choice. I'm aware of the use in some pieces (in competitive booms) of spruce, fir, tamarak, oak, hickory, ebony, bubinga. The best choice totally depends on what a given piece is doing, or being asked to do in a given design. Wood properties that will play into your decisions include density, tensile strength, shear strength, toughness, E (modulus of elasticity-Young's modulus- a measure of the inherent stiffness).

So, do yourself a big favor; review the wiki, then read back through this year's discussions, and last year's.
There is a LOT of discussion of use of wood other than balsa- where, how,why. There are links to extensive information on the properties of a wide variety of woods. When you've done your homework, you'll have some answers, and probably a lot more specific questions. Coming back here with more specific questions you'll probably get much more helpful discussion and answers.

[chinesesushi]

Do you guys have any methods for straightening out pieces of balsa or bass that had bent out of shape?

[Balsa Man]

Do you guys have any methods for straightening out pieces of balsa or bass that had bent out of shape?

First, you're right-on to recognize that trying to build a competitive structure with pieces that aren't straight is a problem.
Second, I'm aware of a lot of tricks to deal with a lot aspects of building booms, bridges, towers, but am not aware of any easy or straightforward ways of straightening a bent piece out.
Third, the best way of avoiding the problem is only using pieces that are very straight.
Fourth, I realize that many folk get faced with the situation of having a pile of wood/sticks where .....most are not straight- either because the coach says, "here's your wood", or you order a bunch of wood, and what arrives is mostly less than straight.

The real, the optimal way of solving the problem, is being able to select sticks/pieces from ....a big pile/selection of wood. For many, if not most, being able to do that is a problem. I've commented a few times over the years on how fortunate we are here to be able to make a half-hour drive down to Specialized Balsa, and sort through hundreds of sticks to get a handfull of sticks at specific density, that are straight, that are stiff, that don't have any visible grain problems. If you get your wood from a local hobby store, you definately want to sort through everything they have, and only buy....useable sticks.

Theoretically, you might be able to take a stick that's....not too crooked, soak it in hot water for a while, hang it under significant tension load, and let it fully dry, and it might come out straighter, and it might hold that straighter shape. I don't think that's a practical solution, though.

VERY few balsa sticks are ....truely straight; "straight" is a relative term. Bass generally tends to have more straighter sticks.

For tension applications (i.e., tension members), a bit of non-straightness is a less serious problem. For compression applications - the compression member(s), straightness is a critical concern.

Buckling - the way a long thin piece/member placed under compression loading along its long axis fails - begins when it suddenly, at some force level, bows out. If you take a perfectly straight stick, put it vertically on a scale, and push straight down on it, what happens? You increase force (see increasing #s on the scale), and suddenly, at some force level, one side pops out into a bow- that bowing/buckling happens toward one of the four faces of the stick. Once that bowing begins, the force/load it will carry without further buckling essentially does not increase; if you keep the same load on that initiated buckling, it bows out further, and breaks. That happens very quickly. If you take another stick that is the same strength, that has a bit of a curve in it, and do the push straight down excercise again, what happens? With very little force, that curve increases; it is, essentially, when you begin to load it, already into buckling failure.

Whether on a long, single piece, or a braced section of a long piece, same story. The straighter the wood, the closer it can come to its theoretical buckling strength.

[baprc]

Hey guys, how far from the testing wall will the base actually be? I understand that this new J-hook allows for a greater height (16.4 cm I believe is what was mentioned). I know that the straight part of the J-hook is 2.5 cm long but the actual base won't rest there, rather at the bottom "corner" of the J-hook. So, how far is that part (if that is where the base rests) from the wall?

[chinesesushi]

First of all, thanks for your help, Balsa Man. I'll look through my pile of balsa wood sticks and find the straight ones.

Hey guys, how far from the testing wall will the base actually be? I understand that this new J-hook allows for a greater height (16.4 cm I believe is what was mentioned). I know that the straight part of the J-hook is 2.5 cm long but the actual base won't rest there, rather at the bottom "corner" of the J-hook. So, how far is that part (if that is where the base rests) from the wall?

I would measure it myself. I would put your base on the J-hook on the wall and measure how far it is to the wall. Or take it off the wall and measure it on a desk. It also depends on where your base design because that would influence where the base would rest, I believe.