Designs

[soccerkid812]

with my tower, i noticed when it broke, that it came apart near the joint
a little wood was stuck to the legs itself(as some of the wood from the bracing was stuck to the leg), so the glue joint itself did not come apart
any theories why this happened?

[yousef213]

Well this is a guess, but I think there are a few possibilities

1. The piece was slightly bent and it snapped out of place

2. There was a lot of stress at the joint but the wood was weaker so it gave 1st

3. Breaking can be unpredictable

4. That may not have been the original spot where it broke, as you probably know, after 1 part breaks, the tower usually crumbles

[soccerkid812]

is it better to use
1. stronger legs and less cross bracing or
2. weaker legs and more cross bracing?

[yousef213]

is it better to use
1. stronger legs and less cross bracing or
2. weaker legs and more cross bracing?

The latter would be better, but only to some extent.

Think about it this way:

The bracings reduce the "Effective" length of a tower dramatically increasing its strength.

Every time you 1/2 its lengnth, you quadruple your strength.

So, in theory, you could reduce your towers wood density by 1/4 and double the bracings, BUT there are a few problems

1. Joint area is greatly reduced and if bracing fails, the tower will quickly follow
2. As you know, balsa is very varied in streghth
3. Bracings also have to carry secounday forces
4. Mathmatically, would it lead to a lighter tower (this is found out by testing)
5. The practicality of it. The thinner the wood the harder to build with.
6. Balsa, like most materials has its strength increased, not linearly, but by an exponentialally as you increase density

Bracings are necessary to prevent buckling, ie I am willing to bet a "skeleton" of a tower with 3/8 x 3/8 will be much weaker than a properly braced tower having 3/16 to 3/16 legs

So basically, its your job, and each of our jobs as builders, to find the corect balance. So, with this in mind, good luck!

[Balsa Man]

As yousef says, it is a matter of tradeoffs- finding the best balance. You can work some out with calculations &/or a spreadsheet, but you’re going to need some testing to really figure it out. You could do compression testing on individual pieces (at different densities), or you could do a whole tower- with a safety tower so you know for sure what failed. If you don’t know what a safety tower is, see picture under 2009 bridges, and previous posts). A couple thoughts and clarifications:

1) The tradeoffs are different in the base/lower portion, and the relatively thin/narrow upper portion; especially in a C-div tower. In the thin upper portion, ladder braces are short; on the order of 5+cm. They’re (in any reasonable bracing scenario) shorter than the leg segments between them. They can be very light and work.

2) The number of ladders/brace points increments, of course, in whole numbers, so the change in # of ladders makes a significant change in the effective column length between them. Using a C-div top as an example- leg length =~35cm. With 4 ladders, one at the bottom, and 3 above it- dividing the legs into 4 equal segments, exposed column length is ~8.6cm. Using 3 ladders, one at the bottom, and two dividing the legs into 3 equal segments, the exposed column length is ~11.9cm

OK, let's throw some real data at it; legs from 3/32nds bass. Light at 1.37gr/24”=0.00244 gr/cm; heavy at 1.97 gr/24”=0.03266 gr/cm. At a column length of 8.6cm, the heavy carries 10.75 g, and the light carries 7.1g. At a column length of 11.9 cm, the heavy carries 5.6g, and the light carries 3.7g.

We’re using 0.7gr/36” balsa (0.0064gr/cm) for ladders, and 1/64th x 3/32nds balsa strips for X-bracing (0.0023 gr/cm). So, for a 3-leg tower-each leg seeing about 5kg at full load, the light, braced at 8.6 provides a nice safety factor (7.1 vs 5kg+). The heavy, braced at 11.9cm intervals provides a marginal, but adequate safety factor (5.5 vs 5kg+). When you calculate it all out , the heavier legs with fewer ladders come to 3.3 gr, and the lighter legs w/ more braces come out to 4.3 gr. However, when you run the numbers for the base section, it comes out the other way by about 0.5 gr (using light bass for the ladders). Some calculating and some smart testing is what it will take to get you to the aanswer of what's best. To me, that's one of the really fun challenges of the event.

[icyfire]

SLM...
Just curious..How well did the tower do itself? As in the whole tower with the base, not the cynlidner only.

[SLM]

SLM...
Just curious..How well did the tower do itself? As in the whole tower with the base, not the cynlidner only.

When we tested the chimney and the base separately, each held the entire load. However, we did not pay close attention to the design and construction of the interface between the chimney and the base. Consequently, the team was not able to correctly vertically align the chimney relative to the base; the chimney ended up tilting to one side by about 5 or so degrees. The tower tipped over under 8kg load at one of our earlier tournaments. We did solve the alignment problem later on and experimented with the design a bit more, but eventually decided to go with an alternative design for the rest of the season.

[stardream23]

I was wondering our tower looks very similar to the Eiffel Tower and it held almost all of 15.5 kg due to out of time, but I want to ask is does anyone have a similar design or is there any room for improvements?

[Littleboy]

I was wondering our tower looks very similar to the Eiffel Tower and it held almost all of 15.5 kg due to out of time, but I want to ask is does anyone have a similar design or is there any room for improvements?

Someone at my regionals from C had something like that. It failed miserably.

[DaBalsa]

This may be kind of random, but I want to hear some opinions. After having been to many competitions...I too have noticed that many schools that usually don't do so well at this type of event are suddenly doing so well. I think this is because of the new scoring system. Although it is good in theory (more realistic), I think they should change it back to how it always was. I actually went to the NY State competition to watch the high schools teams compete in Towers and maybe get some ideas, and here I noticed the same thing. Also, I was watching FM/Spackenkill compete and FM's tower failed completely and I overheard that it had broken after impound, but had a mass of about 7? Maybe less? I couldn't get to taking a picture of it...but they got 41st place. I felt really bad for them, because if the rules hadn't changed, they would most likely have done much more decently. So essentially if a team that has worked really hard to develop a tower that could hold the entire load with a low mass had something bad happen to the tower (like FM), then the event would be a complete bomb because of the new scoring system. What say you?