Boomilever B/C

[balsa]

My state is over and this year is over for me. For this type of event, will there be any rule changes? (I'll be in division C. Would it most likely stay the same; 15cm as height?)

Yes, we typically change the parameters of the construction events from year to year. Not sure yet what we'll do with Boomilever though.

Are there any known possibilities? It seems like making it less than 15 cm would make it impossible to hold full 15 kg, as well as length manipulation... Is something like what happened with towers, where a scoring system encompassed dimensions likely?

I don't think they will make it less than 15cm. Maybe lengthening the boom length itself, some other changes perhaps.

[Unbihexium]

Yes, we typically change the parameters of the construction events from year to year. Not sure yet what we'll do with Boomilever though.

Are there any known possibilities? It seems like making it less than 15 cm would make it impossible to hold full 15 kg, as well as length manipulation... Is something like what happened with towers, where a scoring system encompassed dimensions likely?

I don't think they will make it less than 15cm. Maybe lengthening the boom length itself, some other changes perhaps.

Either way the whole issue with that is that any manipulation of the distal angle might make any sort of efficiency near 2000 impossible as it was nearly so this year. 15 cm was already pushing it. Maybe they'll change it to be like towers with the scoring system counting the dimensions...

[fanjiatian]

I'm trying to justify a design that tapers from the base to the distal end
I don't see any benefits: wouldn't there be more net force + shear on the compression members? They'd have to be longer since it gets narrower towards the distal end

Would it create more stability near the loading block?

[iwonder]

Could you elaborate on the tarpered part? Is it a compression boom with a tapered compression member? Or some other design.

[fanjiatian]

Sorry for not being clear!
So if the compression members are 5 cm apart when they touch the testing wall, then the compression members will be less than 5 cm apart where the loading block goes.
If you looked at the boomilever from an aerial view, the compression members would look more like a trapezoid or triangle instead of a rectangle.

[iwonder]

Ahh, so if it creates more stability than compression members that are less than 5 cm apart on both ends I assume. Well sure, it would be more stable that way, but it's really a weight vs benefit problem. For me, because of my design I can't make the distal end narrower than 5cm or the loading block doesn't fit, but it you could, you'd need slightly heavier bracing on the wall end because there's a small spreading force on the end beams(though honestly the friction in the wall would probably hold most of that) and then you'd need a lot heavier distal end connection because the loading block would(in most cases) get in the way of the tension members. This would force you to move the tension members back, and you'd see an actual cantilever section on the distal end(think of a diving board) and that'd require a very stiff distal end to hold, even over the 2.5-3.5cm distance.

Overall, you'd probably have to test distal end configurations to hole it, and see if it saves enough weight to be worth it. But while you're doing that why not just make both ends narrower? As long as the width is grater than or equal to the height if the compression member then technically the extra bracing is just wasted wood.

[fanjiatian]

Ohh that makes a lot of sense!
I just realized that this configuration wouldn't work for mine either
In mine, the connection between the tension and compression member is aligned with the center of the loading block, so the minimum (and really maximum) distance apart my compression members can be is 5 cm.

Now that I think about it, this was a big problem last year. Often the loading block would slip through the compression members without actually breaking anything.

[iwonder]

Yeah, that happened to me a few times, I eventually looked down the end of the boom and relized that my compression members were spreading out. All I had to do was add a little member across the bottom that was in tension to hold them together, added like .12g and my boom held twice as much