Boomilever B/C

[knightmoves]

im sure someone has answered this before but how significant is the strength between 1/16 x 1/16 and 1/32 x 1/16?

In tension or in compression? It's not the same.

Look up Euler's critical load, and you'll find that it scales like the area moment of inertia, which for a rectangle is a b^3. So in compression, there's a factor of 8 difference in strength between the two sections you list (assuming all else is equal). In tension, it scales like the cross-section, so there's only a factor of 2 difference (but in reality it might be even less, because tension pieces often fail by ripping the wood apart at the glue joint, so you don't get the full effect of the thickness.)

[xiangyu]

For compression pieces, is a bigger cross area and lower density better or smaller area but higher density better? (Assuming both have the same weight).

What does that look like for tension pieces?

[knightmoves]

For compression pieces, is a bigger cross area and lower density better or smaller area but higher density better? (Assuming both have the same weight).

This is a great thing to measure. Balsa Man in years past described the "single finger push down" method for measuring the buckling strength of a stick of balsa. Cur a suitable length of balsa, hold it vertically with the bottom end resting on a scale, and push down with a single finger on the top of the stick until the measured force plateaus. That's your buckling strength. Do this for balsa sticks of the same length, but varying size and density. See what you learn.

[MadCow2357]

For compression pieces, is a bigger cross area and lower density better or smaller area but higher density better? (Assuming both have the same weight).

What does that look like for tension pieces?

IMO, I'd take the larger cross-sectional area piece over the high-density piece with less CS area. Depends on the numbers/stats of those pieces though. However, note that wood pieces that are very low density are subject to a phenomenon dholdgreve dubbed "blow out", when a glue connection on your boom doesn't fail but the area immediately around your glue connection on your low-density piece does. At this point, it doesn't matter really how strong your other members are or how strong your glue connection, the wood itself WILL fail at a certain load (that's bad). Be careful when building light guys.

For tension members, I use bass, just because it has a much more uniform density (and consistency in wood strength). I'm more likely to get a "bad egg" with balsa. In reference to your first question, higher density lower cross-section area has worked well for me.

[Things2do]

Both of the Boomilevers that I've ever built failed at the attachment point. The attachment point was made from two pieces of bass with a piece of balsa laminated in the middle, and the second one was pre-dented by standing on it while it was laying on my Mousetrap Vehicle's rod. I laminated it with B.S.I. Instacure +, the purple bottle. The first time, at Regions, it split the piece of bass touching the hook in half, then it separated from the tension member on the side that split off. The second time, at State, it separated from one of my tension members without splitting. I know that the first one split because I didn't depress it where the hook was, which broke the bond with the tension member. For the second one, I firmly glued the attachment point to my tension members with C.A. from the same bottle, but it detached somewhere around 5 or 6 kilograms. What can do to improve the strength of those joints?

{Sorry for the essay. And, yes, I've only built two total.}

[jinhusong]

Use Gorilla Glue.

[klastyioer]

Use Gorilla Glue.

any particular reason why you would use gorilla glue over like bsi gapfilling

[jinhusong]

Use Gorilla Glue.

any particular reason why you would use gorilla glue over like bsi gapfilling

No particular reason. We are just familiar with gorilla glue. We used it to fill gap of RC airplanes.

Last season, we tried gorilla glue in "unit test" and found it can hold 40 kg with two 1/16X1/16 basswood glue to a basswood base with 0.5 inch overlap. The other ends of basswood sticks were glued to a board with 2 inch overlap by CA. We use luggage scale to pull the board while the base on the hook. (Maybe we should also test with CA, to see how short it still can hold the 40 kg).

Jinhu

[dankdecidueye]

Hey everyone!

What's the most competitive type of boomilever this year? When I mean type of boomilever I mean in terms of box, tube, etc., so which one would we see get the highest scores?

[RobertYL]

What's the most competitive type of boomilever this year? When I mean type of boomilever I mean in terms of box, tube, etc., so which one would we see get the highest scores?

Because of the width limitation, I believe the only two viable competitive designs that have been seen in the past would be the tower chimney booms and the basic tension booms. I've tested out box booms in the past but the weight reduction is not worth the effort unless you are working with large beams which will greatly lower your efficiency.