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Another problem: is balsa stronger in tension or compression? I've heard that balsa is better in tension, but the wiki here: http://scioly.org/wiki/index.php/Boomilever#Wood states that balsa is better in compression than tension?

You want to center the loading block with the distal end, as close to 45 cm as possible
Balsa definitely has a stronger tensile strength than compression, about 60% higher. But you can increase its compression strength by decreasing its effective length through bracings ( tension strength does not vary with length

So who says the distal end has to support the entire loading block? Why can't the last few cm of the block hang off the end?


(Oh, and please click the edit button instead of posting twice)

Haha, I could technically make my compression member 45.7 cm if I was using a 36 inch piece...
But isn't that a bit too much hanging off the end? There's a risk of the loading block sliding off especially if there's bowing in the compression member right?
Can somebody clarify?

fanjiatian wrote:Haha, I could technically make my compression member 45.7 cm if I was using a 36 inch piece...
But isn't that a bit too much hanging off the end? There's a risk of the loading block sliding off especially if there's bowing in the compression member right?
Can somebody clarify?

Don't worry about the loading block slipping off. there is enough downwards force to prevent that to happen, and your boom prob wouldn't bow to that point that it slides off. If you are feeling kind of uncertain still, I simply have a small piece perpendicular to the compression members connecting the two. I don't use it for that reason, but it should qualm your fears.

fanjiatian wrote:Haha, I could technically make my compression member 45.7 cm if I was using a 36 inch piece...
But isn't that a bit too much hanging off the end? There's a risk of the loading block sliding off especially if there's bowing in the compression member right?
Can somebody clarify?

It's definitely fine to have some of the loading block hang off the compressions, but I wouldn't suggest too much. (46 cm sounds pretty reasonable, but I haven't tried it). The first boom I made, I didn't read the rules correctly... and didn't see that the middle of the loading block had to be at 40-45 cm XD So I made my boomilever 40 cm. At competition, the event coordinator informed me, and I had to slide the loading block to the very end with only half of it on the compressions this caused it to bend a lot more than if I had made it a little longer, so it didn't do very well. Somehow I still got 6th, but it could've been much better if I read the rules more closely and made it longer. Granted, if you design for hanging, you might have more luck.

Looks like a new phrase in the rules this year, "The Contact Depth must not be more than 20.0 cm (Div. B) or 15.0 cm (Div. C) prior to loading." Is anyone else tempted to build a springy appendage that "contacts" at 15 cm but then springs away as the bucket fills so the main compression member touches down at the bottom of the testing wall? I'd hate to be the only team at BARSO working the idea.

does the loading block count as part of the weight for the boomilever

aznman908 wrote:does the loading block count as part of the weight for the boomilever

Nope, it counts as part of the testing weight with the sand, so in the end, its weight is included. The same goes for the bucket.

Should the base be an upside down U that literally hooks onto the J-hook or should we just continue with last year's style by drilling a hole through a base and slipping that over the hook? Also, is there a hex nut or washer that goes over the base to secure it to prevent it from sliding?

One more thing, has anyone experimented with tube boomilevers lately, and if so, how did they do?