Tower Weight

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arv101
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Tower Weight

Post by arv101 »

I always find towers that say that their weight as 5 grams or less but I don't understand how it is made. I build the same exact design with same type of wood and everyting but my towers always weigh more. Can somene please help me ! I am a studier but I wish to also become a builder so to get into my school team I have to get an effiecncy that is over 1500. Also can you guys give me some tips. Thanks
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Re: Tower Weight

Post by Crtomir »

arv101 wrote:I always find towers that say that their weight as 5 grams or less but I don't understand how it is made. I build the same exact design with same type of wood and everyting but my towers always weigh more. Can somene please help me ! I am a studier but I wish to also become a builder so to get into my school team I have to get an effiecncy that is over 1500. Also can you guys give me some tips. Thanks
Well, to start with, you can read through all the posts in the "Towers B/C" section of this forum. That will get you a lot of information on building the tower.

As to the weight issue, you need to be weighing each balsa piece before you cut it to get the density, and then weigh again after you cut it to make sure that piece fits your weight budget. You should make a weight budget (in a spreadsheet like Excel or Google Sheets) that lists the desired dimensions (length, width, height, volume), density, and weight of each piece and then sums them together to get the total weight. Then add a certain percent or amount for the glue (3% to 6% of total weight is probably good, if you use the glue sparingly). Once you have your design laid out, you can create this kind of weight budget pretty easily in a spreadsheet form. Then you can play around with changing the densities of your wood and see how that affects the final weight.

Do you measure the combined weight of all the pieces before you assemble them? Is that combined weight less than 5g? If all the pieces weigh less than 5g, but your tower weighs much more than 5g after you assemble it, then maybe you are using too much glue? What kind of glue are you using? CA glue (super glue) is the most common and doesn't add a lot to the weight unless you overdo it.

What do you mean (exactly) when you say
arv101 wrote:same type of wood and everything
? I suspect we can find your solution if we carefully examine what is contained within that statement.

It can be done. So don't despair. Most likely you need to use wood that is less dense. The only way to know the density of the wood is to measure it carefully. Our kids spend countless hours measuring wood density.
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Re: Tower Weight

Post by Random Human »

Crtomir wrote:
arv101 wrote:I always find towers that say that their weight as 5 grams or less but I don't understand how it is made. I build the same exact design with same type of wood and everyting but my towers always weigh more. Can somene please help me ! I am a studier but I wish to also become a builder so to get into my school team I have to get an effiecncy that is over 1500. Also can you guys give me some tips. Thanks
Well, to start with, you can read through all the posts in the "Towers B/C" section of this forum. That will get you a lot of information on building the tower.

As to the weight issue, you need to be weighing each balsa piece before you cut it to get the density, and then weigh again after you cut it to make sure that piece fits your weight budget. You should make a weight budget (in a spreadsheet like Excel or Google Sheets) that lists the desired dimensions (length, width, height, volume), density, and weight of each piece and then sums them together to get the total weight. Then add a certain percent or amount for the glue (3% to 6% of total weight is probably good, if you use the glue sparingly). Once you have your design laid out, you can create this kind of weight budget pretty easily in a spreadsheet form. Then you can play around with changing the densities of your wood and see how that affects the final weight.

Do you measure the combined weight of all the pieces before you assemble them? Is that combined weight less than 5g? If all the pieces weigh less than 5g, but your tower weighs much more than 5g after you assemble it, then maybe you are using too much glue? What kind of glue are you using? CA glue (super glue) is the most common and doesn't add a lot to the weight unless you overdo it.

What do you mean (exactly) when you say
arv101 wrote:same type of wood and everything
? I suspect we can find your solution if we carefully examine what is contained within that statement.

It can be done. So don't despair. Most likely you need to use wood that is less dense. The only way to know the density of the wood is to measure it carefully. Our kids spend countless hours measuring wood density.

Agreed with Crtomir, look around in the forums and you will find good info as to how to reduce weight and improve score.. Another factor is just building both precisely and efficiently. A precise tower with all four sides balanced is neccesary to improve score, as an imbalanced tower will distribute more weight to certain legs, leading to a less efficient tower. And building a lot of towers, and pinpointing mistakes is a key improving your score. Try simply overbuilding a tower, say 12 grams holding all weight... (using last years rules I assume). Then try to see where you can bring the weight down by a gram or half a gram, every time you build, soon you will hit your goals. If you are aiming for 1500, all it will take is some dedication, precise building, and understanding of the physics encompassing this event.

Hope this helps
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Re: Tower Weight

Post by Balsa Man »

arv101 wrote:I always find towers that say that their weight as 5 grams or less but I don't understand how it is made. I build the same exact design with same type of wood and everyting but my towers always weigh more. Can somene please help me ! I am a studier but I wish to also become a builder so to get into my school team I have to get an effiecncy that is over 1500. Also can you guys give me some tips. Thanks
I agree with Crtomir and Random Human.
Did you read the fairly long post in the "17-18 Season-Building over the summer" thread, immediately below this one, where I reviewed some of the basics, and how to do exactly what you're asking about?? That you are a studier is a good thing. If you apply that studying skill to all the good info that's here (and much more that will develop as the season progresses), you will learn how to make a very competitive tower. :geek:
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Re: Tower Weight

Post by arv101 »

Crtomir wrote:
arv101 wrote:I always find towers that say that their weight as 5 grams or less but I don't understand how it is made. I build the same exact design with same type of wood and everyting but my towers always weigh more. Can somene please help me ! I am a studier but I wish to also become a builder so to get into my school team I have to get an effiecncy that is over 1500. Also can you guys give me some tips. Thanks
Well, to start with, you can read through all the posts in the "Towers B/C" section of this forum. That will get you a lot of information on building the tower.

As to the weight issue, you need to be weighing each balsa piece before you cut it to get the density, and then weigh again after you cut it to make sure that piece fits your weight budget. You should make a weight budget (in a spreadsheet like Excel or Google Sheets) that lists the desired dimensions (length, width, height, volume), density, and weight of each piece and then sums them together to get the total weight. Then add a certain percent or amount for the glue (3% to 6% of total weight is probably good, if you use the glue sparingly). Once you have your design laid out, you can create this kind of weight budget pretty easily in a spreadsheet form. Then you can play around with changing the densities of your wood and see how that affects the final weight.

Do you measure the combined weight of all the pieces before you assemble them? Is that combined weight less than 5g? If all the pieces weigh less than 5g, but your tower weighs much more than 5g after you assemble it, then maybe you are using too much glue? What kind of glue are you using? CA glue (super glue) is the most common and doesn't add a lot to the weight unless you overdo it.

What do you mean (exactly) when you say
arv101 wrote:same type of wood and everything
? I suspect we can find your solution if we carefully examine what is contained within that statement.

It can be done. So don't despair. Most likely you need to use wood that is less dense. The only way to know the density of the wood is to measure it carefully. Our kids spend countless hours measuring wood density.
Thanks, I don't precisly measure the density however I do weigh the pieces. I get my wood from online (balsa) and it usually comes in two densities one that is foam like and the other that is denser and stiffer. I use the stiffer one for my base and the foam for my trusses. The dimensions are 1/8 X 1/8 for the main legs and 1/16 X 1/16 for the trusses. For glue I use gorrila glue. I have a total of 9 X 's spaced equally for my best design so far. I read in a forum that 1/16 X 1/32 is used however I don't have a stripper that can strip so thin and I don't know where to buy it so can someone recomend a way I could get this wood? I appreciate your help :)
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Re: Tower Weight

Post by Unome »

arv101 wrote:I read in a forum that 1/16 X 1/32 is used however I don't have a stripper that can strip so thin and I don't know where to buy it so can someone recomend a way I could get this wood? I appreciate your help :)
You may be able to buy a 1/32" sheet and strip it into 1/16" sticks, though I'm not certain how well this would work (i don't know much about the subject).
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Re: Tower Weight

Post by Crtomir »

arv101 wrote:
Crtomir wrote:
arv101 wrote:I always find towers that say that their weight as 5 grams or less but I don't understand how it is made. I build the same exact design with same type of wood and everyting but my towers always weigh more. Can somene please help me ! I am a studier but I wish to also become a builder so to get into my school team I have to get an effiecncy that is over 1500. Also can you guys give me some tips. Thanks
Well, to start with, you can read through all the posts in the "Towers B/C" section of this forum. That will get you a lot of information on building the tower.

As to the weight issue, you need to be weighing each balsa piece before you cut it to get the density, and then weigh again after you cut it to make sure that piece fits your weight budget. You should make a weight budget (in a spreadsheet like Excel or Google Sheets) that lists the desired dimensions (length, width, height, volume), density, and weight of each piece and then sums them together to get the total weight. Then add a certain percent or amount for the glue (3% to 6% of total weight is probably good, if you use the glue sparingly). Once you have your design laid out, you can create this kind of weight budget pretty easily in a spreadsheet form. Then you can play around with changing the densities of your wood and see how that affects the final weight.

Do you measure the combined weight of all the pieces before you assemble them? Is that combined weight less than 5g? If all the pieces weigh less than 5g, but your tower weighs much more than 5g after you assemble it, then maybe you are using too much glue? What kind of glue are you using? CA glue (super glue) is the most common and doesn't add a lot to the weight unless you overdo it.

What do you mean (exactly) when you say
arv101 wrote:same type of wood and everything
? I suspect we can find your solution if we carefully examine what is contained within that statement.

It can be done. So don't despair. Most likely you need to use wood that is less dense. The only way to know the density of the wood is to measure it carefully. Our kids spend countless hours measuring wood density.
Thanks, I don't precisly measure the density however I do weigh the pieces. I get my wood from online (balsa) and it usually comes in two densities one that is foam like and the other that is denser and stiffer. I use the stiffer one for my base and the foam for my trusses. The dimensions are 1/8 X 1/8 for the main legs and 1/16 X 1/16 for the trusses. For glue I use gorrila glue. I have a total of 9 X 's spaced equally for my best design so far. I read in a forum that 1/16 X 1/32 is used however I don't have a stripper that can strip so thin and I don't know where to buy it so can someone recomend a way I could get this wood? I appreciate your help :)
First, I'd recommend using super glue (CA glue). You can pick this up at a hobby shop or even a hardware store. http://www.loctiteproducts.com/p/4/2/sg ... Bottle.htm is good enough.

Second, you should actually start measuring/calculating densities. This will allow us to understand what you are working with (to better help you) and also allow you to make your results reproducible.

Third, you should order online (or buy from local hobby shop) a balsa stripper like this one: https://www.amazon.com/Master-Airscrew- ... B0000WS5OQ. That will allow you to strip thinner pieces for the X-braces. What we do is start with a 1/16" x 3" x 36" flat piece of balsa and strip 1/32" strips from it to give 1/16" x 1/32". You can adjust the width of the strips to something in between 1/32" and 1/16" if you need stiffer X-braces. 1/16" x 1/16" X-braces can work to start with though. Here is what I would do....

Find 4 pieces of 1/8" x 1/8" x 36" balsa sticks that all weigh about 1.8g. They need to be nearly identical weight and stiffness. These will be your legs. Then, find ten to twenty 1/16" x 1/16" x 36" balsa sticks that each weigh between 0.25g and 0.30g. Don't use if more than 0.3g. These will be your X-braces. Do 9 braces up each of the four sides. This should give you a decent tower to start with. Then, you can play around with reducing wood densities from there. That should give you about 4.0g-4.5g for the combined weight of all four legs and hopefully another 4g or less for the X-braces. So, let's say it ends up as 8g. That's a good tower. Even without the bonus, your score would be 15000/8 = 1875. You don't have to go to super light weight (<5g) right away. Start with a basic structure that you know you can build reliably and repeatably getting consistent results every time. Then, try to drop the densities down a little.

Are you using a jig to help build the tower? You should because the legs need to be aligned precisely.
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Re: Tower Weight

Post by Balsa Man »

A couple of quick comments-

Agree with Crtomir; this is all good guidance. But, getting into things a little more:

On weighing/measuring/tracking density, if you’re weighing your sticks, you’re measuring density. Using that information in design, and optimizing a design is just a matter of units. Density can be expressed in various ways; pounds per cubic foot, grams per cc- all weight per some volume unit. One convenient form is simply grams per 36" (with stick size stated). For example, the 1/8"x1/8"x36" sticks Crtomir recommends starting with would be 1.8gr/36". A 1/8x36 stick weighing 1.98 grams is 10% more dense/heavier (1.8 + 0.18(10% of 1.8); a 1/8x36 stick weighing 1.62gr would be 10% lighter/less dense. A form that’s really helpful in doing tower weight estimates (at first, and as you work to optimize wood selection) is grams per centimeter. For example, that 1.8gr/36” stick is 1.8gr/91.6cm, which = 0.01965gr/cm.

As has been explained many times here in the Towers forum,
a) balsa comes/exists in a very wide range of density. At 1/8x36 there exist/you can get, sticks weighing from 0.7 up to 4.7gr. That's a big range
b) there is a relationship between density and strength. Higher density is stronger (in both tensile strength, and buckling strength-how a piece will fail under axial compression loading). Roughly, doubling the density will increase strength by a factor of around 2.4X.
c) failure will happen at the weakest piece/link. If you have 4 legs, and one is weaker than the others, it will fail first.
c) while there is a relationship between density and strength, there is also significant variability; you can see as much as +/-20%. So, you can have, say 20 1/8 x 36” sticks that all weigh 1.8gr. If you measure their buckling strength (how to do this is explained in great detail in previous posts), you’ll see a distribution- most in the middle, a few significantly stronger, a few significantly weaker. So, if you just take 4 sticks weighing the same for 4 legs, you may well have one or more that are much weaker. So, you build a tower with them, let’s say using 9Xs for bracing, it breaks at say a 10kg load, you conclude 1.8gr/36 legs aren’t strong enough. That would mean you’d need to either increase leg density, or decrease your bracing interval (say going from 9 Xs to 10Xs). But if its one weak leg you’re basing that conclusion on (and you haven’t measured the relative strengths), it could turn out that 4 really good 1.7, or even 1.6… maybe even 1.5gr/36” leg sticks would hold full load. You do want 4 well matched legs, but you want that match in strength. Getting really competitive means you’ve gotten to the very lightest pieces that will just barely carry the ‘design forces’- the forces they see at full load.

On cutting/stripping 1/32 sheet for Xs. The longer the length you’re trying to cut, the harder it is to get it right. The longest you’ll need is around 33-34cm, so 14”- no need to try to strip or cut at 36”. Just cut off a 14” piece of the sheet. For shorter Xs, shorter pieces of your sheet(s).

Personally, I haven't used a stripper in years. With a plastic cutting board, a good steel ruler/straight edge, a razor blade, masking tape, and a cutting width guide piece, and a bit of practice (working with Jr High kids, they typically have it down within 10-ish cuts), You can cut more consistently.
Tape sheet piece to be cut on cutting board, so tape covers ~1/8” of sheet ends. Starting from one side, put ruler, with cutting guide strip (for cutting 1/16 wide strips, use a piece of 1/16 x 1/16) aligned with long edge of the sheet.. When lined up, push down/hold the ruler in place with 2 fingers. Move the guide strip out of the way. While holding ruler firmly down, cut gently with razor blade. Figure on making 2 passes to make the cut. Be sure to keep razor blade vertical throughout the cut.
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Re: Tower Weight

Post by arv101 »

Crtomir wrote:
arv101 wrote:
Crtomir wrote:
Well, to start with, you can read through all the posts in the "Towers B/C" section of this forum. That will get you a lot of information on building the tower.

As to the weight issue, you need to be weighing each balsa piece before you cut it to get the density, and then weigh again after you cut it to make sure that piece fits your weight budget. You should make a weight budget (in a spreadsheet like Excel or Google Sheets) that lists the desired dimensions (length, width, height, volume), density, and weight of each piece and then sums them together to get the total weight. Then add a certain percent or amount for the glue (3% to 6% of total weight is probably good, if you use the glue sparingly). Once you have your design laid out, you can create this kind of weight budget pretty easily in a spreadsheet form. Then you can play around with changing the densities of your wood and see how that affects the final weight.

Do you measure the combined weight of all the pieces before you assemble them? Is that combined weight less than 5g? If all the pieces weigh less than 5g, but your tower weighs much more than 5g after you assemble it, then maybe you are using too much glue? What kind of glue are you using? CA glue (super glue) is the most common and doesn't add a lot to the weight unless you overdo it.

What do you mean (exactly) when you say ? I suspect we can find your solution if we carefully examine what is contained within that statement.

It can be done. So don't despair. Most likely you need to use wood that is less dense. The only way to know the density of the wood is to measure it carefully. Our kids spend countless hours measuring wood density.
Thanks, I don't precisly measure the density however I do weigh the pieces. I get my wood from online (balsa) and it usually comes in two densities one that is foam like and the other that is denser and stiffer. I use the stiffer one for my base and the foam for my trusses. The dimensions are 1/8 X 1/8 for the main legs and 1/16 X 1/16 for the trusses. For glue I use gorrila glue. I have a total of 9 X 's spaced equally for my best design so far. I read in a forum that 1/16 X 1/32 is used however I don't have a stripper that can strip so thin and I don't know where to buy it so can someone recomend a way I could get this wood? I appreciate your help :)
First, I'd recommend using super glue (CA glue). You can pick this up at a hobby shop or even a hardware store. http://www.loctiteproducts.com/p/4/2/sg ... Bottle.htm is good enough.

Second, you should actually start measuring/calculating densities. This will allow us to understand what you are working with (to better help you) and also allow you to make your results reproducible.

Third, you should order online (or buy from local hobby shop) a balsa stripper like this one: https://www.amazon.com/Master-Airscrew- ... B0000WS5OQ. That will allow you to strip thinner pieces for the X-braces. What we do is start with a 1/16" x 3" x 36" flat piece of balsa and strip 1/32" strips from it to give 1/16" x 1/32". You can adjust the width of the strips to something in between 1/32" and 1/16" if you need stiffer X-braces. 1/16" x 1/16" X-braces can work to start with though. Here is what I would do....

Find 4 pieces of 1/8" x 1/8" x 36" balsa sticks that all weigh about 1.8g. They need to be nearly identical weight and stiffness. These will be your legs. Then, find ten to twenty 1/16" x 1/16" x 36" balsa sticks that each weigh between 0.25g and 0.30g. Don't use if more than 0.3g. These will be your X-braces. Do 9 braces up each of the four sides. This should give you a decent tower to start with. Then, you can play around with reducing wood densities from there. That should give you about 4.0g-4.5g for the combined weight of all four legs and hopefully another 4g or less for the X-braces. So, let's say it ends up as 8g. That's a good tower. Even without the bonus, your score would be 15000/8 = 1875. You don't have to go to super light weight (<5g) right away. Start with a basic structure that you know you can build reliably and repeatably getting consistent results every time. Then, try to drop the densities down a little.

Are you using a jig to help build the tower? You should because the legs need to be aligned precisely.
Thanks for all the help, I know what a jig is but don't know how to make it... I have seen metal and heavy cardboard jigs but is their any lighter material that I could use? Also how to I make t?
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Re: Tower Weight

Post by Balsa Man »

If you go back to pages 6, 7, 8 of the Towers B/C thread, there is some detailed explanation, and drawings. There is more detailed 'how to' info scattered through the next 30 or so pages, also.
Understand, the approach to building a jig I described is but one way to 'skin the cat'

There are many ways to solve the problem, which is making a precise, symmetrical 3-dimensional shape/structure upon which the legs are held in your 'design configuration' sufficiently.....firmly to allow you to put bracing on.
The materials will need to depend on a) how much time and effort you want to put in, b) how precise is good enough for you, c) what tools you have or can get access to, and how good at using them you are, or become.
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