Towers B/C

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MadCow2357
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Re: Towers B/C

Post by MadCow2357 »

Crtomir wrote:
MadCow2357 wrote:
MadCow2357 wrote:I've read through the whole forum, looking for density guidelines when buying balsa. I dug up Balsa Man's (may he rest in peace) explanation on why 1/8 legs are more weight-strength efficient than 3/32 and 1/16 legs, and a couple of other gold mines of info as well. But, I have not found any concrete answer to my current issue.

How to explain? First of all, I have decided to go light for the last 2 towers I will build before states. I went on the Specialized Balsa website, and looked at the "Specially Weighed" 1/16 Square Balsa sticks. I was initially preparing to just click a low density option, and hope for the best, when I came across a table of specific densities from 0.2 to 1.2 grams per 36" stick. My issue is, I cannot determine if a certain density of Balsa is suitable for the goal that I am trying to achieve. Maybe 0.2 is way too lightweight and weak, or maybe it is considered a moderately lightweight density (what I want)? I don't know.

Maybe someone can help give me a guideline to which densities of 1/16x1/16 and 1/8x1/8 are considered lightweight, mid range, and heavy. I don't want the balsa to be overly light, and carry barely any weight, nor do I want to have a 20 gram tower that held the full load like last time (990 is a super cruddy score, even for a rookie like me ;) ).

I am aiming for a ~8 gram tower that can carry near full load. Even a 10 gram would be fine to get gold at states (RI is not competitive). A link to a picture of my tower:
https://drive.google.com/file/d/1mcqaf0 ... sp=sharing
https://drive.google.com/file/d/10y3tuF ... sp=sharing
https://drive.google.com/file/d/17C4O9A ... sp=sharing
https://drive.google.com/file/d/1ZRe1kL ... sp=sharing

I hope I didn't make this post sound disrespectful in any way. For some weird reason, I feel like the wording of this post was a little haughty or demanding, even though I didn't mean it that way. Maybe it's just nothing... :?
I think you would probably want to start with 1/8" x 1/8" x 36" sticks for your columns (legs) that weigh 1.2g and then start dropping down to 1.0g once you get the bracing figured out. To calculate the density, you do this:

1.2g / [(1/8)*(1/8)*(36)] = 2.1 g/in^3

To change this to lb/ft^3, multiply by 3.81 to get 2.1 g/in^3 * 3.81 = 8.13 lb/ft^3

That falls in the "Light Balsa" category (6-10 lb/ft^3) for Specialized Balsa. However, last time I ordered from them, they had run out of wood in that category. Maybe they have more now, I don't know. My guess is between the CA wildfires destroying balsa trees and the uptick in Science Olympiad orders, they might be out of stock. That was a month or so ago.

Hope this helps.
Thanks for the quick response. Will order 1.1, I guess. Recommendations on the 1/16x1/16?

Btw, do you have any opinions on my design, besides it being rectangular base?
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Re: Towers B/C

Post by Crtomir »

MadCow2357 wrote: Thanks for the quick response. Will order 1.1, I guess. Recommendations on the 1/16x1/16?

Btw, do you have any opinions on my design, besides it being rectangular base?
Well, I would order a range of densities. Like I say, we usually order "Light Density" from Specialized Balsa.

As far as the design of your base, we never really considered a rectangular design like you have. We have always used a square base. I'm curious if a rectangular design could perform better. Are you building with a jig? see that you have a tension "strap" at the bottom to keep the two sides from sliding apart and that is good. You would probably still need this tension strap at the bottom if you went with a square tower trying to get the bonus. (It would be at the bottom of all four sides.) That's what we do.

Also, how thick are your braces? They seem thick in the pictures, but I can't tell for sure. We have been using something like 1/16" x 1/32" for the braces. These we strip from a 1/16" x 4" x 36" piece that weighs about 18g. Then we make sure that each 1/16" x1/32" x 36" piece we cut is between 0.20g and 0.25g. Definitely don't want more than 0.30g. That really starts to add up weight on your tower if your braces are too heavy.

Be careful about the tension strap also. Make that light. It's easy to make the tension strap too heavy, even heavier than the legs of the base! Remember, balsa is very strong under tension, even with low density wood. Not so for compression.

Also, build and test, build and test, build and test. That's really the only way. Everyone will tell you that, but it's so true. Last year, two of our girls built 37 towers before they finally got over 3000 points. This year they didn't build as many because the towers took longer to build. Still, build and test, build and test.
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Re: Towers B/C

Post by Crtomir »

Also, because of your rectangular base design, you found that you needed to use essentially 8 legs for your base. That's going to add a lot of weight. Maybe that's why it's better to go with a simpler square base design. Stick with simple. Simple works. Last year, almost all the top Towers teams at Nationals had pretty much the same design. Square base, no bonus, 10-12 X-braces all the way up each side. No "ladders", nothing fancy, just X-braces. Very simple design, but it works.
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Re: Towers B/C

Post by MadCow2357 »

Crtomir wrote:
MadCow2357 wrote: Thanks for the quick response. Will order 1.1, I guess. Recommendations on the 1/16x1/16?

Btw, do you have any opinions on my design, besides it being rectangular base?
Well, I would order a range of densities. Like I say, we usually order "Light Density" from Specialized Balsa.

As far as the design of your base, we never really considered a rectangular design like you have. We have always used a square base. I'm curious if a rectangular design could perform better. Are you building with a jig? see that you have a tension "strap" at the bottom to keep the two sides from sliding apart and that is good. You would probably still need this tension strap at the bottom if you went with a square tower trying to get the bonus. (It would be at the bottom of all four sides.) That's what we do.

Also, how thick are your braces? They seem thick in the pictures, but I can't tell for sure. We have been using something like 1/16" x 1/32" for the braces. These we strip from a 1/16" x 4" x 36" piece that weighs about 18g. Then we make sure that each 1/16" x1/32" x 36" piece we cut is between 0.20g and 0.25g. Definitely don't want more than 0.30g. That really starts to add up weight on your tower if your braces are too heavy.

Be careful about the tension strap also. Make that light. It's easy to make the tension strap too heavy, even heavier than the legs of the base! Remember, balsa is very strong under tension, even with low density wood. Not so for compression.

Also, build and test, build and test, build and test. That's really the only way. Everyone will tell you that, but it's so true. Last year, two of our girls built 37 towers before they finally got over 3000 points. This year they didn't build as many because the towers took longer to build. Still, build and test, build and test.
Crtomir wrote:Also, because of your rectangular base design, you found that you needed to use essentially 8 legs for your base. That's going to add a lot of weight. Maybe that's why it's better to go with a simpler square base design. Stick with simple. Simple works. Last year, almost all the top Towers teams at Nationals had pretty much the same design. Square base, no bonus, 10-12 X-braces all the way up each side. No "ladders", nothing fancy, just X-braces. Very simple design, but it works.
Well, kind of wish that I asked this question earlier. Anyways, yesterday night I decided to order 1.8 gram for 1/8, and 0.4 for 1/16. I calculated that the 1/8 will account for about 4.25 grams, and the 1/16 bracing will weigh about 0.5 grams in total. I am estimating that I will use about 2 grams of glue (Many joints, and I use a ton of glue :? ). that would bring me to a 6.75 gram tower that I am hoping will hold full load, or near it. I would score 2963, which would be an all time high for me! But, as many people have said before, math only works if everything is perfect. I will probably score somewhere in the low 2000s for this one, which would still be VERY GOOD FOR ME! My top is 1184 right now, 13 grams and 10.8 kg held. Not so good...
But this is my first time doing a balsa structures event, and 1500 can win gold at RI, so I'm pretty hyped! If I can score 2000, I will beat last year's tower (1133) by almost 900 points. And last year's 1133 won gold.

To address your about the rectangular base, I did start with a square tower. But, I did not understand the importance of a one piece jig at that time, so I built the tower entirely without a jig. I built the top half and the bottom half separately, and that tower scored 680 :cry: . So, I decided to build a rectangular base tower like my local high school's team did. They also gave me their jig, because they made a new one, so I was all set to build a rectangular tower. I find rectangular towers easier to build, as I just create 2 sides and lace them together.

However, if I had more time before competition, I would definitely use the time to design a good square tower, as well as build a good one piece jig out of clear acrylic. After doing more and more research to understand the concepts, I am becoming increasingly dissatisfied with what I have accomplished, and my decision to build rectangular base towers.
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Re: Towers B/C

Post by Unome »

MadCow2357 wrote:I am estimating that I will use about 2 grams of glue (Many joints, and I use a ton of glue :? ).
You can easily shave off 75% of this without losing any structural integrity. Most joints only require in the range of 5-10 micrograms of glue or less.
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Re: Towers B/C

Post by Crtomir »

MadCow2357 wrote:Well, kind of wish that I asked this question earlier. Anyways, yesterday night I decided to order 1.8 gram for 1/8, and 0.4 for 1/16. I calculated that the 1/8 will account for about 4.25 grams, and the 1/16 bracing will weigh about 0.5 grams in total. I am estimating that I will use about 2 grams of glue (Many joints, and I use a ton of glue :? ). that would bring me to a 6.75 gram tower that I am hoping will hold full load, or near it. I would score 2963, which would be an all time high for me! But, as many people have said before, math only works if everything is perfect. I will probably score somewhere in the low 2000s for this one, which would still be VERY GOOD FOR ME! My top is 1184 right now, 13 grams and 10.8 kg held. Not so good...
But this is my first time doing a balsa structures event, and 1500 can win gold at RI, so I'm pretty hyped! If I can score 2000, I will beat last year's tower (1133) by almost 900 points. And last year's 1133 won gold.

To address your about the rectangular base, I did start with a square tower. But, I did not understand the importance of a one piece jig at that time, so I built the tower entirely without a jig. I built the top half and the bottom half separately, and that tower scored 680 :cry: . So, I decided to build a rectangular base tower like my local high school's team did. They also gave me their jig, because they made a new one, so I was all set to build a rectangular tower. I find rectangular towers easier to build, as I just create 2 sides and lace them together.

However, if I had more time before competition, I would definitely use the time to design a good square tower, as well as build a good one piece jig out of clear acrylic. After doing more and more research to understand the concepts, I am becoming increasingly dissatisfied with what I have accomplished, and my decision to build rectangular base towers.
I don't see how using 1.8g for the 1/8" x 1/8" x 36" sticks to use as the main columns (legs) of your tower is going to get you a 6.75g tower. Measure the length of your legs (base and top "chimney") and multiply by 4 to get the total length of all legs. The height of the tower is at least 50cm, right? So because the base is diagonal, you will use more than 50cm per leg, but lets just say you had 50cm on each leg, that would be 200cm total for all 4 legs, right? So your total weight for just the legs would be

1.8g * 200cm / 36in = 1.8g * 200cm / 91.4cm = 4.2g

But your tower design has essentially 8 legs on the base and 4 on the chimney, so the total length of all your legs together is probably more like 4* 80cm = 320cm. That would give you

1.8g * 320cm / 36in = 1.8g * 320cm / 91.4cm = 6.3g

So, I'm guessing that just the columns (legs) of your tower alone will add up to at least 6g. Then you have all the bracing and glue to factor in. Bracing starts to add up. Really. Also, don't use so much glue. It should be only about 0.2g-0.3g total if you are careful.

Of course if you use 1.8g columns, you don't need nearly as many bracing intervals to support the columns, but it won't cut your weight down that much. I'm guessing you will have a 9-10g tower.

The real question is how much weight can your tower support? How much weight has your tower been holding so far?
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Re: Towers B/C

Post by Raleway »

Just a quick tip: do NOT base your success relative to whatever data you have on your state rivals. If I knew my rivals were at 2.5k, and I hit 2.6k, I would simply just think that they were great at Towers and could hit 3k. Of course, not every state is equal in builds, but overpreparing for that one chance each year pays off. Furthermore, do not base scores on last year's data. They've been relatively same scale but are not totally comparable.
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Re: Towers B/C

Post by MadCow2357 »

Crtomir wrote:
MadCow2357 wrote:Well, kind of wish that I asked this question earlier. Anyways, yesterday night I decided to order 1.8 gram for 1/8, and 0.4 for 1/16. I calculated that the 1/8 will account for about 4.25 grams, and the 1/16 bracing will weigh about 0.5 grams in total. I am estimating that I will use about 2 grams of glue (Many joints, and I use a ton of glue :? ). that would bring me to a 6.75 gram tower that I am hoping will hold full load, or near it. I would score 2963, which would be an all time high for me! But, as many people have said before, math only works if everything is perfect. I will probably score somewhere in the low 2000s for this one, which would still be VERY GOOD FOR ME! My top is 1184 right now, 13 grams and 10.8 kg held. Not so good...
But this is my first time doing a balsa structures event, and 1500 can win gold at RI, so I'm pretty hyped! If I can score 2000, I will beat last year's tower (1133) by almost 900 points. And last year's 1133 won gold.

To address your about the rectangular base, I did start with a square tower. But, I did not understand the importance of a one piece jig at that time, so I built the tower entirely without a jig. I built the top half and the bottom half separately, and that tower scored 680 :cry: . So, I decided to build a rectangular base tower like my local high school's team did. They also gave me their jig, because they made a new one, so I was all set to build a rectangular tower. I find rectangular towers easier to build, as I just create 2 sides and lace them together.

However, if I had more time before competition, I would definitely use the time to design a good square tower, as well as build a good one piece jig out of clear acrylic. After doing more and more research to understand the concepts, I am becoming increasingly dissatisfied with what I have accomplished, and my decision to build rectangular base towers.
I don't see how using 1.8g for the 1/8" x 1/8" x 36" sticks to use as the main columns (legs) of your tower is going to get you a 6.75g tower. Measure the length of your legs (base and top "chimney") and multiply by 4 to get the total length of all legs. The height of the tower is at least 50cm, right? So because the base is diagonal, you will use more than 50cm per leg, but lets just say you had 50cm on each leg, that would be 200cm total for all 4 legs, right? So your total weight for just the legs would be

1.8g * 200cm / 36in = 1.8g * 200cm / 91.4cm = 4.2g

But your tower design has essentially 8 legs on the base and 4 on the chimney, so the total length of all your legs together is probably more like 4* 80cm = 320cm. That would give you

1.8g * 320cm / 36in = 1.8g * 320cm / 91.4cm = 6.3g

So, I'm guessing that just the columns (legs) of your tower alone will add up to at least 6g. Then you have all the bracing and glue to factor in. Bracing starts to add up. Really. Also, don't use so much glue. It should be only about 0.2g-0.3g total if you are careful.

Of course if you use 1.8g columns, you don't need nearly as many bracing intervals to support the columns, but it won't cut your weight down that much. I'm guessing you will have a 9-10g tower.

The real question is how much weight can your tower support? How much weight has your tower been holding so far?
I want to cry right now... Because you are definitely right on the fact that I messed up the calculations. But you may have underestimated how much I messed up on this...

Let me explain what I did wrong. First, I only calculated the weight of one side. Second, I miscounted the bracings for a single side. Third, I only accounted for the bracings that would lace the two sides together. Lastly, I did not order enough wood. This all said, I believed that I could get a 6.75 gram tower when I would actually get a 11.39 gram tower. Not so good, eh? :cry:

Here is a link to the revised data and calculations:
https://docs.google.com/document/d/169h ... sp=sharing
https://drive.google.com/file/d/1sRQwF3 ... sp=sharing

I guess I will just reorder wood, since I have decided to switch from 1.8g 1/8 sticks and 0.4g 1/16 sticks to 1.2g 1/8 sticks and 0.3g 1/16 sticks. Should I order enough for 2 towers?
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Re: Towers B/C

Post by MadCow2357 »

Crtomir wrote:The real question is how much weight can your tower support? How much weight has your tower been holding so far?
The first rectangular tower that I built was 13 grams, and it held 10.8 kilograms, scoring 1184. It probably could have held near the full load, but the tower tipped over when we were loading it, causing a couple of braces to come off.

The second was 20.2 grams, and it held the full load, scoring 990. It is now sitting in a box as my team's backup tower, in case the competition tower breaks.

I am guessing that this tower will hold near full load. Btw, how large should a triangular gusset plate be?
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Re: Towers B/C

Post by MadCow2357 »

Raleway wrote:Just a quick tip: do NOT base your success relative to whatever data you have on your state rivals. If I knew my rivals were at 2.5k, and I hit 2.6k, I would simply just think that they were great at Towers and could hit 3k. Of course, not every state is equal in builds, but overpreparing for that one chance each year pays off. Furthermore, do not base scores on last year's data. They've been relatively same scale but are not totally comparable.
Will keep this in mind... And I agree that over preparing is never a bad idea as long as you can get everything else done, too. As for beating last year's score, I want bragging rights. :D
Last edited by MadCow2357 on April 7th, 2018, 11:41 am, edited 1 time in total.
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