Scioly.org

bernard wrote:

Clueless Builder wrote:I'm C.

My newest tower held 15kg at 6.4g.

Congratulations, "Clueless Builder!" Did you attempt the bonus?

Getting pretty close to breaking Balsa Man's predictions for top national scores (~2400 if I remember correctly).

Unome wrote:

bernard wrote:

Clueless Builder wrote:I'm C.

My newest tower held 15kg at 6.4g.

Congratulations, "Clueless Builder!" Did you attempt the bonus?

Getting pretty close to breaking Balsa Man's predictions for top national scores (~2400 if I remember correctly).

If it qualifies for the bonus, that's better than my guess. Very well done.

I'm just curious guys, when you mean "test" the tower you mean you put all the weight possible on it and make it break, right?

How do you fix the tower after that?

I have invitationals coming up.. I want to test my tower out to see how much it can hold but I don't want to break it. I don't have a second one to use, do you guys have more than one tower?

hearthstone224 wrote:I'm just curious guys, when you mean "test" the tower you mean you put all the weight possible on it and make it break, right?

How do you fix the tower after that?

I have invitationals coming up.. I want to test my tower out to see how much it can hold but I don't want to break it. I don't have a second one to use, do you guys have more than one tower?

Testing does indeed result in breaking - usually, anyway. The balsa pros can tell you all about partial loading (put a small amount of weight on your competition tower, just to make sure there's no glaring weakness, like a member you didn't glue properly) and about the subsequent performance of towers that were tested to hold max weight without breaking, but, most of the time, testing your tower will lead to breakage. This is good, because you'll see exactly where it fails - make sure to document your test with slow-motion video!

It's definitely a time constraint issue, when you're a week away from a competition. If you know that you and your partner can build a replica tower to equal or better precision within a few hours, then, go for it! But, if it's taken you a long time to build, you don't want to test it and discover that the design works great - and not leave yourself enough time to build the next one as carefully.

Many people have given this advice before - find the design you like, and just refine that same design with each new tower, rather than start completely from scratch. That way, after a few tests, you'll be reasonably confident about how your tower will perform at competition, without having to fully test it.

Edit: Also - don't bother with "fixing" your tower. If a member falls off without breaking, glue it back on, but when the tower breaks, it will be rendered useless. I don't think there are any techniques that would let you achieve the same efficiency with a broken/fixed tower, and if there are, they'd surely take longer than building a new tower from scratch.

SPP SciO wrote:

hearthstone224 wrote:I'm just curious guys, when you mean "test" the tower you mean you put all the weight possible on it and make it break, right?

How do you fix the tower after that?

I have invitationals coming up.. I want to test my tower out to see how much it can hold but I don't want to break it. I don't have a second one to use, do you guys have more than one tower?

Testing does indeed result in breaking - usually, anyway. The balsa pros can tell you all about partial loading (put a small amount of weight on your competition tower, just to make sure there's no glaring weakness, like a member you didn't glue properly) and about the subsequent performance of towers that were tested to hold max weight without breaking, but, most of the time, testing your tower will lead to breakage. This is good, because you'll see exactly where it fails - make sure to document your test with slow-motion video!

It's definitely a time constraint issue, when you're a week away from a competition. If you know that you and your partner can build a replica tower to equal or better precision within a few hours, then, go for it! But, if it's taken you a long time to build, you don't want to test it and discover that the design works great - and not leave yourself enough time to build the next one as carefully.

Many people have given this advice before - find the design you like, and just refine that same design with each new tower, rather than start completely from scratch. That way, after a few tests, you'll be reasonably confident about how your tower will perform at competition, without having to fully test it.

Edit: Also - don't bother with "fixing" your tower. If a member falls off without breaking, glue it back on, but when the tower breaks, it will be rendered useless. I don't think there are any techniques that would let you achieve the same efficiency with a broken/fixed tower, and if there are, they'd surely take longer than building a new tower from scratch.

Well said, SPP SciO, I concur fully. I think with the time problem, running what you have is the way to go. Particularly important is the advise on settling on a design and refining it. We've had lots of discussion this year on how to figure out what leg wood, with what bracing interval will work. If you're working with that, you should be in pretty good shape. We've also had good discussion on the importance of a good jig, so that you take the shape/configuration variable out when building a second, third, etc. tower- shape stays the exact same, you just make adjustments to wood; that's how you get a true replica. Its important, of course, that you carefully align joints each time to take away any variability in that factor. You should have a record of the density and buckling strength of legs and ladders (at least a buckling strength reading of the full/36" sticks the legs/ladders are taken from.

To see/capture/understand where it fails, you will need good high frame rate/slow motion video. When the initial failure mode happens, it happens really fast, particularly if the load is..... getting up toward max, and within....less than 1/100th of a second, secondary damage starts happening. There is one alternative to see/understand what's failing, a "safety tower"- making a tripod out of like 1x2s, that's big enough to be like 6-8" taller than the tower, and wide enough to be outside the tower at the base. From the top of it you hang an inverted eye-bolt- threaded end down. You set it up so the lower end of the hanging eye-bolt is, oh, a 1/4" above the upper threaded end of the eye-bolt that goes through the load block. Then you put a coupling nut (which is like an inch long, with 1/4" threaded inside) joining the eye bolt ends, and adjust so the eye-bolt through the load block can only drop/move down like 1/8th" (when the tower fails and its no longer supported in its initial position). That way you avoid secondary damage.

Hm, interesting information. I'll do what you guys say, I don't think it would be wise to test my tower now.

Um, how do you attach pictures? I can't find a button that says upload. I want to post a picture of my first tower so you guys can critique it.

Thanks.

hearthstone224 wrote:Hm, interesting information. I'll do what you guys say, I don't think it would be wise to test my tower now.

Um, how do you attach pictures? I can't find a button that says upload. I want to post a picture of my first tower so you guys can critique it.

Thanks.

Upload the image somewhere (like your google drive), get a shareable link, and use the IMG tag to embed the picture in the post.

OK here's the top view:



Here's the side view.



As you can probably tell, its not so accurate. I haven't fully tested it yet but it weighs a lot compared to other people's towers. Like a lot more.

Like 35 g. hahaaa...

But yeah, its already held 15 pounds and I don't dare to go further, I'm probably going to wait for the competition.

Also, first tower so can't beat myself up too hard

Thanks for sharing the pics!

I've gotta say, with all the previous discussion on how to test/select wood that will give you sufficient strength, and how to do bracing, I'm really surprised at a 35gr weight, even though its a first build. I assume 1/8" balsa, yes? That's a LOT of weight! (even with really excessive glue use, which I don't see)
What (36") stick weights did you use (legs and bracing)?

I did use 1/8 balsa, and sadly I cannot tell you the weight of our legs because I didn't keep track of the ones I used for legs/bracing. I know, my bad.

But for legs we went for legs with strengths of about 50-70 BS and for bracing we used more lighter sticks (like ones with strengths of 30-50).

Yeah, probably won't get a very good score (calculated it, will be about 375).