Towers B/C

[Gr8tor]

Ivy Spear, I use light 1/8 wood and 1/16 and it works fine. Some people use 1/32 wood for braces though I think.

[Balsa Man]

So I spent some time reading through the thread and this is basically what I got out of it (Excluding the mathematic formulas):

1) This year must be a double part tower, with a wide base truncated pyramid as the base and a perfectly vertical chimney as the upper portion

2) It would be prudent to shoot for the bonus this year, since it offers too much value to be ignored

3) It's very hard to build a tower whose base and chimney matches up perfectly, but using a jig would help with this. I have a question, if I don't have the means to build an accurate jig, are there are steps I can take to try to build as accurately as possible without one? Tips, order in which I should build etc.

4) You should build the chimney and the base separately then connect them? Not sure on this one

5) All X bracings are superior to including a ladder, but this year you do want ladders on your upper chimney portion? Then we don't need them for the lower base portion I assume? Also the ladders should be in between the two main beams correct? Not on the outside.

6) The beams for X bracings should not be square? Or is it fine if they are. How would you cut them out from sheets anyway? Will I have to buy balsa sheets from an online website?

7) The meta position for the X bracings is on the outside of the tower. Wouldn't that warp one or both of the X bracings in that scenario though? Can someone attach a picture since a picture is worth a thousand words

Additionally, how thick should the main, longer legs be? Is 1/8" too much already? Will 1/16" braces work in general, or are there some exceptions?

Also, I'm not very satisfied with the current cutter I have (It's an X-ACTO Knife), so are there any alternatives?

Thanks and sorry for asking so much, I just wanted to clear some things up

1)This year must be a double part tower, with a wide base truncated pyramid as the base and a perfectly vertical chimney as the upper portion
Yes except for the chimney-for stability, you want a bit of lean-in on the chimney legs. At the 8cm circle level (<20cm above the test base for C-Div, <25cm above test base for B-Div, you want a….fairly tight fit (2-3mm on each side), so you don’t have to lean the base in any more than you have to. That means the legs at that point are far enough apart they won’t support the 5cm square load block, so you have to lean the chimney legs in some to get them fitting underneath the load block.
2) It would be prudent to shoot for the bonus this year, since it offers too much value to be ignored
Yes, beyond prudent, if you want to be competitive….
3) It's very hard to build a tower whose base and chimney matches up perfectly, but using a jig would help with this. I have a question, if I don't have the means to build an accurate jig, are there are steps I can take to try to build as accurately as possible without one? Tips, order in which I should build etc.
I’ll let others speak to this. As I’ve said many times, I really think the most important thing to do if you want to be competitive is to put time into making as good a jig as you can. As reflected in my post going over ways to do a jig, there are ways, with simple, inexpensive materials, and hand tools (straightedge and razor blade/Xacto knife, posterboard/cardboard/foam board) to do a jig that will give you good ‘shape control’ – better than you can do trying to build two sides on a template, and then trying to join them into a symmetrical tower. It is not just to get chimney and base leg segments to match/join up precisely, it is to get the entire tower symmetrical, and vertical (no lean to one side- center of top vertically above center of base.
4) You should build the chimney and the base separately then connect them? Not sure on this one
No, exactly the opposite! It is very difficult, even if you did two separate jigs (one for base, one for chimney), and those jigs were with good precision, to get a good, symmetrical tower, and the angle cut where the leg segments join done so the cross section of both segments, where they meet, the same
5) All X bracings are superior to including a ladder, but this year you do want ladders on your upper chimney portion? Then we don't need them for the lower base portion I assume? Also the ladders should be in between the two main beams correct? Not on the outside.
Yes, it appears that all Xs (using 1/16” x 1/32” X strips) do have a weight/performance advantage over ladders and Xs. As I’ve said, at least a couple of times, you absolutely need a ladder at the top of the base section, and you need one right at the top of the tower, but except for those two ladders, all Xs. Ladders should be same size as the legs (1/8”), and, yes, installed between adjacent legs. If put on outside leg faces, they will have to be heavier (higher density) to work (because of non-axial loading).
6) The beams for X bracings should not be square? Or is it fine if they are. How would you cut them out from sheets anyway? Will I have to buy balsa sheets from an online website?
Not sure what you mean by “beams” of the X braces, but, as discussed a few times, it looks like Xs 1/16” wide cut from 1/32” sheet are the way to go (not square – e.g., 1/16x1/16). You’d cut them with a razor blade and metal straight edge, and a bit of practice. Cut the sheet into shorter pieces before strip cutting (the shorter the piece you’re cutting strips from, the easier it is to get them straight/accurate; Long enough you have extra at each end to handle them when glueing on, but not a lot of excess. So for Xs in the chimney, maybe 14, 15, 16cm long; for the lower Xs in the base, 30-35cm long. Good hobby stores generally carry 1/32” sheet as an option to on line. And remember you’ll be able to use lower density for short Xs, and will need higher density for the long Xs
7) The meta position for the X bracings is on the outside of the tower. Wouldn't that warp one or both of the X bracings in that scenario though? Can someone attach a picture since a picture is worth a thousand words
Not sure what you mean, “meta position”, but yes, as described, they go on the outside faces of the legs. Yes, because the ends of both strips in an X pair are in the same plane, and they cross, there will be a very slight bow in both- with 1/32” thickness, each bowed about 1/64” (and after installed, you do a glue spot where they cross)
Additionally, how thick should the main, longer legs be? Is 1/8" too much already? Will 1/16" braces work in general, or are there some exceptions?
First, terminology alignment; “legs”= the 4 main upright members; each leg with two “segments” (upper/”chimney”, and lower “base” section), joined by ‘braces’; horizontal braces = “ladders”, sloped/diagonal = Xs. As discussed, before, 1/8” (square) legs is what you’ll see in virtually all competitive towers. There is a small theoretical weight advantage by going to 5/32” legs (less than 0.3gr in a B tower, half that in a C tower. Smaller than 1/8” for legs will put you at a serious disadvantage. We’ve discussed bracing pieces sizing above
Also, I'm not very satisfied with the current cutter I have (It's an X-ACTO Knife), so are there any alternatives?
Assume you’re talking about cutting leg sticks. I think you’ll find a fine-toothed razor saw (used with very gentle pressure, especially on low density wood) will work much better
Thanks and sorry for asking so much, I just wanted to clear some things up
Absolutely nothing to feel sorry about; that's what this board is here for; feel free to keep asking as your understanding grows and new questions come up.

One last, quick comment re: your comment, "Excluding the mathematic formulas"
It may seem daunting, but it is important understand/remember that 'the science' of how structures work, and designing/engineering structures (S.O. towers in this instance) is based in, and expressed in, mathematical relationships. To do well in any Science Olympiad event, you have to come to an understanding of the science the event is about. So, don't be put off by it; read, study, think about it, play with it, ask questions about it.

[Balsa Man]

Balsa Man, Would you need a mask and gloves for that? Also, a little off topic, how do you create and send your design to the people who laser cut? What software do you use? AutoCad?

I need to say, read the label, follow the safety instructions. I've simply advised there is a significant hazard if used improperly. Consult with parents and coach. Other plastic cements (while a little...less potent) have similar chemicals and hazards. Working with it under a lab hood, or outside is a reasonable approach.
Gloves not a bad idea for pouring from the can it comes in to applicator bottle.

For laser cutting, I simply provided precise dimensions (horizontal dimensions at the base plane, at the 8cm circle plane, and at the top plane, vertical dimensions at the 8cm circle ant top plane), on a drawing done in Excel (drawing reasonably close, but by no means precise/to scale). It's the dimensions they need to input to the cutter.

[IvySpear]

1)This year must be a double part tower, with a wide base truncated pyramid as the base and a perfectly vertical chimney as the upper portion
Yes except for the chimney-for stability, you want a bit of lean-in on the chimney legs. At the 8cm circle level (<20cm above the test base for C-Div, <25cm above test base for B-Div, you want a….fairly tight fit (2-3mm on each side), so you don’t have to lean the base in any more than you have to. That means the legs at that point are far enough apart they won’t support the 5cm square load block, so you have to lean the chimney legs in some to get them fitting underneath the load block.
2) It would be prudent to shoot for the bonus this year, since it offers too much value to be ignored
Yes, beyond prudent, if you want to be competitive….
3) It's very hard to build a tower whose base and chimney matches up perfectly, but using a jig would help with this. I have a question, if I don't have the means to build an accurate jig, are there are steps I can take to try to build as accurately as possible without one? Tips, order in which I should build etc.
I’ll let others speak to this. As I’ve said many times, I really think the most important thing to do if you want to be competitive is to put time into making as good a jig as you can. As reflected in my post going over ways to do a jig, there are ways, with simple, inexpensive materials, and hand tools (straightedge and razor blade/Xacto knife, posterboard/cardboard/foam board) to do a jig that will give you good ‘shape control’ – better than you can do trying to build two sides on a template, and then trying to join them into a symmetrical tower. It is not just to get chimney and base leg segments to match/join up precisely, it is to get the entire tower symmetrical, and vertical (no lean to one side- center of top vertically above center of base.
4) You should build the chimney and the base separately then connect them? Not sure on this one
No, exactly the opposite! It is very difficult, even if you did two separate jigs (one for base, one for chimney), and those jigs were with good precision, to get a good, symmetrical tower, and the angle cut where the leg segments join done so the cross section of both segments, where they meet, the same
5) All X bracings are superior to including a ladder, but this year you do want ladders on your upper chimney portion? Then we don't need them for the lower base portion I assume? Also the ladders should be in between the two main beams correct? Not on the outside.
Yes, it appears that all Xs (using 1/16” x 1/32” X strips) do have a weight/performance advantage over ladders and Xs. As I’ve said, at least a couple of times, you absolutely need a ladder at the top of the base section, and you need one right at the top of the tower, but except for those two ladders, all Xs. Ladders should be same size as the legs (1/8”), and, yes, installed between adjacent legs. If put on outside leg faces, they will have to be heavier (higher density) to work (because of non-axial loading).
6) The beams for X bracings should not be square? Or is it fine if they are. How would you cut them out from sheets anyway? Will I have to buy balsa sheets from an online website?
Not sure what you mean by “beams” of the X braces, but, as discussed a few times, it looks like Xs 1/16” wide cut from 1/32” sheet are the way to go (not square – e.g., 1/16x1/16). You’d cut them with a razor blade and metal straight edge, and a bit of practice. Cut the sheet into shorter pieces before strip cutting (the shorter the piece you’re cutting strips from, the easier it is to get them straight/accurate; Long enough you have extra at each end to handle them when glueing on, but not a lot of excess. So for Xs in the chimney, maybe 14, 15, 16cm long; for the lower Xs in the base, 30-35cm long. Good hobby stores generally carry 1/32” sheet as an option to on line. And remember you’ll be able to use lower density for short Xs, and will need higher density for the long Xs
7) The meta position for the X bracings is on the outside of the tower. Wouldn't that warp one or both of the X bracings in that scenario though? Can someone attach a picture since a picture is worth a thousand words
Not sure what you mean, “meta position”, but yes, as described, they go on the outside faces of the legs. Yes, because the ends of both strips in an X pair are in the same plane, and they cross, there will be a very slight bow in both- with 1/32” thickness, each bowed about 1/64” (and after installed, you do a glue spot where they cross)
Additionally, how thick should the main, longer legs be? Is 1/8" too much already? Will 1/16" braces work in general, or are there some exceptions?
First, terminology alignment; “legs”= the 4 main upright members; each leg with two “segments” (upper/”chimney”, and lower “base” section), joined by ‘braces’; horizontal braces = “ladders”, sloped/diagonal = Xs. As discussed, before, 1/8” (square) legs is what you’ll see in virtually all competitive towers. There is a small theoretical weight advantage by going to 5/32” legs (less than 0.3gr in a B tower, half that in a C tower. Smaller than 1/8” for legs will put you at a serious disadvantage. We’ve discussed bracing pieces sizing above
Also, I'm not very satisfied with the current cutter I have (It's an X-ACTO Knife), so are there any alternatives?
Assume you’re talking about cutting leg sticks. I think you’ll find a fine-toothed razor saw (used with very gentle pressure, especially on low density wood) will work much better
Thanks and sorry for asking so much, I just wanted to clear some things up
Absolutely nothing to feel sorry about; that's what this board is here for; feel free to keep asking as your understanding grows and new questions come up.

One last, quick comment re: your comment, "Excluding the mathematic formulas"
It may seem daunting, but it is important understand/remember that 'the science' of how structures work, and designing/engineering structures (S.O. towers in this instance) is based in, and expressed in, mathematical relationships. To do well in any Science Olympiad event, you have to come to an understanding of the science the event is about. So, don't be put off by it; read, study, think about it, play with it, ask questions about it.

Thank you so much for your detailed response . I apologize for my ambiguous terminology, I'm still a relative newbie compared to most here.

I think I'll attempt to build a jig since you emphasized it so much (I'm sort of afraid that it'll make my tower worse if I build it slightly off)

But if I did have a jig, would I be building the tower on the jig? Or first build the faces according to a template then attach them with the guidance of the jig?

Also, since I'm rather unsure of how well I can cut out 1/16" by 1/32" X's, I'd like to specify how bad are square 1/16" by 1/16" X's? I'm building my first tower for school tryouts, so the competition there isn't too intense. But if 1/16" by 1/16" X's are significantly detrimental to the tower, then I think I'll try to get my hands on some balsa sheets.

Also, the image I had when you said "fine-toothed razor saw" was this giant three foot long saw with jagged teeth in my garage. Can you elaborate a bit more? Sorry I just don't want to go out and buy the wrong thing

And since you said that figuring out the math was worth the time, I guess my first question would be why are ladders unnecessary? I don't know if that's math related, but in my head it's pretty hard to grasp that such thin X braces' can withstand the compression from a full load (Sorry if it's not called compression). I also looked over the spreadsheet, and I was wondering what is efficient length and what is SFPD?

Every time one of my questions is answered, I just have more questions about it

[Balsa Man]

Thank you so much for your detailed response. I apologize for my ambiguous terminology, I'm still a relative newbie compared to most here.

You’re very welcome. And no need for apology; its helpful for you and anyone else if we work to establish a common vocabulary.

I think I'll attempt to build a jig since you emphasized it so much (I'm sort of afraid that it'll make my tower worse if I build it slightly off)

OK, first, a little discussion of context. One of the challenges of trying to be a resource here on Scioly is what level do you speak to. There are folk, at one end of the spectrum, that come along and are more of a newbie than you are (and don’t have a coach or parent who has any idea what/how to teach in terms of how to create a decent tower). At the other end of the spectrum, there are folk who have studied a lot, and built a lot, have won at the State level; who have medaled at Nationals, There are students, ranging from first year middle schoolers to high school seniors, so what they have been exposed to, and what they can be expected to understand and use (in terms of math and science concepts, and other things) varies widely. There are coaches, ranging from new teachers just jumping in to S.O. who are just as newbie as you are, to some that have been doing this for many years, who understand the math/physics/engineering, who understand the tools and techniques needed to turn a concept/design into physical reality, and have guided students to a very high level of success for years (w/ towers, bridges, and boomilevers- the three rotating S.O. ‘wood structures’ events.

The other important context is just how good a result are you looking for and willing to chase? Providing sound/correct guidance to someone who was top 10 or 15 at Nationals last year, and is really committed to doing what it takes to do even better this year involves very different topics and level of detail than would be helpful to someone new to the event, is committing an hour or two a week, and would be really happy to place mid-pack at Regionals/Invitationals.

There are a number of us who have… been at this game for a number of years, believe it is important to help students have access to good information that will help them,,, reach their personal goals.

Finally, back to your concern…. As I’ve said many times, yes, I believe a good jig is the biggest, most important step one can take to move from…mediocrity to … competitiveness. To do that you have to take control of ‘the variables.’ A jig allows you to take control of the shape variable; the shape of the tower. As I’ve discussed many times, if each tower you build is different in shape, you have no way to understand/learn from testing what adjustments to make to improve performance/score. When I say ‘different in shape’, I’m not talking big differences- a sixteenth of an inch in a few places will make a big difference in performance. High performance is all about getting to the lightest set of pieces that will just carry the forces they see in a loaded tower. At least if a jig is… off, not symmetrical, and one leg is getting disproportional loading, it will be consistent; make that leg a little stronger, and it’ll hold. You’re correct that if you build a jig that… looks like the leaning tower of Pisa, the towers you build with it… won’t do well. As in many aspects of life, you get back what you put in. Whatever style/type of jig you choose to use, you want to work really hard, as in time invested, and care and precision applied to get it precise and symmetrical.

But if I did have a jig, would I be building the tower on the jig? Or first build the faces according to a template then attach them with the guidance of the jig?

Yes, absolutely you would; a very fundamental thing-that is what a jig is for. It is a structure that holds the legs in precise, symmetrical alignment/position in three dimensional space. With the legs held in place, you then put on the bracing pieces. That alignment/positioning comes from your basic design- that….idealized set of lines that creates a shape that meets the dimensional rules. Math/science/engineering allows you to know/calculate the forces each of the pieces see when the tower is under load. The wood selection process then allows you to find/get to the lightest pieces that will carry those ‘design forces.’ That’s why ‘shape control’ is so important – if the pieces in the created structure are not all in the alignment/position of ‘the design’, then the forces that one or more of those pieces see when under load will be significantly more than the design forces, and that’s where it will break. It will always break first at the weakest link.

Also, since I'm rather unsure of how well I can cut out 1/16" by 1/32" X's, I'd like to specify how bad are square 1/16" by 1/16" X's? I'm building my first tower for school tryouts, so the competition there isn't too intense. But if 1/16" by 1/16" X's are significantly detrimental to the tower, then I think I'll try to get my hands on some balsa sheets.

How “bad”? Two … ‘aspects of badness’ First is the bowing that comes from them crossing- twice as much as you’ll get with X strips that are 1/32 thick (half as thick). They have to be able to deal with both compression and tension forces, depending on which direction a leg is… trying to deform under load. If that deformation is pulling on an X (putting a tension load on), then the bowing means it can/will (with very little force) be pulled out longer. That will allow the braced point on the leg to move farther in the direction it is trying to deform. That is the beginning of buckling, and once it starts, it keeps happening, and the leg snaps. Same situation if deformation is pushing on the end of an X strip (putting a compression load on)- the more the strip is bowed, the less force it takes to complete buckling; the weaker it will be. Second aspect is weight. Without getting into a pretty complicated discussion of why and how, my current understanding is that 1/16 x 1/32 will be more efficient – lighter while providing the needed strength- than 1/16 x 1/16. That said, I’m not talking a lot lighter; haven’t run detailed calculations on how much. Less than a gram- 4, 5, 6 tenths, maybe. Not a big deal if you’re talking a 10gr tower; a big deal if you’re talking a 5gr tower…

For sure, cutting X strips is the biggest pain in the tail (and time suck) in construction of an ‘all Xs’ tower. Back in last year’s towers forum, I provided pretty detailed instruction on how to consistently cut strips w/ razor blade and straightedge. But if you’re chasing all the little angles to improved/high performance, this is an important and real one.


Also, the image I had when you said "fine-toothed razor saw" was this giant three foot long saw with jagged teeth in my garage. Can you elaborate a bit more? Sorry I just don't want to go out and buy the wrong thing

I’m talking about one of these-
https://www.amazon.com/Xacto-X75350-Ext ... B000BREQIO

Not so scary, huh?

And since you said that figuring out the math was worth the time, I guess my first question would be why are ladders unnecessary? I don't know if that's math related, but in my head it's pretty hard to grasp that such thin X braces' can withstand the compression from a full load (Sorry if it's not called compression). I also looked over the spreadsheet, and I was wondering what is efficient length and what is SFPD?

Every time one of my questions is answered, I just have more questions about it

Heck, that’s how learning – and science - works; like peeling off the layers of an onion. One question and answer leads to a new one or ones. Start with a very simple (over-simplified) understanding, work through layer after layer of understanding, end up with a much more detailed, complex, but more correct understanding.

In grasping how X strips can handle the forces they may see at full tower load (which, as discussed above may be tension or (yes, you are correct) compression forces), couple of things.
Assuming a good symmetrical tower –
First, forces on the X strips (with tower under 15kg load) are on the order of a kilogram, certainly less than 2. If you measure the buckling strength of say a 15cm long one, it is going to be… well less than 1kg, less than 100gr. Because the Xs are glued together at the crossing point, cutting length in half, in-place strength will approach 4x that at full length (the basic inverse square relationship of length to buckling strength (BS)). Does that….fully explain things? No. I’ve posted a number of times on this, discussing how I fully understand the math/engineering of a ladders and Xs bracing system to the point of being able to apply it ‘predictively’; measure leg wood BS, multiply that by effective length factor (of 2.3), from that, calculate bracing interval, calculate BS needed in ladders, put it all together, and it works- carries full load, and also posted about how I do not yet have a comparable mathematical/engineering handle on the all Xs approach; how we switched from a ladders and Xs bracing system after State, for Nationals, and how we ‘reverse-engineered’ using design (wood spec) data I’d gotten from a couple of teams with high performing all Xs towers; how the reverse engineering allowed us to calculate an effective length factor for all Xs bracing (using 1/8” legs, and 1/16 x 1/32 Xs, and as I posted, that EL factor, which is about 0.55. As I posted after Nationals last year, that value worked; both the B tower and C tower I was working with held full load, got into top 15. So, can’t yet explain the theoretical basis, but can say, absolutely it works.

“Efficient length” and “SFPD” – First, it says “effective length.” Second, both terms, what they’re about, how to use them are explained in some detail in this thread- long post near the top of page 6, and long post near the bottom of page 1. If you go back to the archived towers board from 2017, there is a bunch of detailed discussion on how effective length works within Euler’s Buckling Theorem, what it is, and is all about. It goes through and describes the learning process we went through as we …peeled back that deeper layer of the onion and figured out that understanding and using effective length – and getting to a correct effective length factor - was necessary to correctly calculate wood strength needed for members working under compression loading.

So, what does this say? I’m not just saying this to you, but to others working to ‘figure it all out’; to learn and understand what it takes to design and construct a ‘good tower’, or a ‘really good tower.’ –
This forum is far and away the most comprehensive collection of good information on tower design and construction out there; it is a textbook, an engineering manual, that a number of us have contributed to. When I say ‘this forum’, I mean all the threads in “Towers”, this season and last season. Reading with comprehension, studying, just like you study for classes at school will take you miles down the road to understanding. It will set you up to be able to ask new questions that will take you deeper into the onion (if you’re really chasing high performance), or that will get you to good questions about ‘how can I streamline using this information, just want a reasonable tower that doesn’t take a lot of time/effort/money?

Hope this helps.

[cheese]

Just a heads up, if you are ever looking for the definition of something, or more into a certain topic, you can use the search bar at the top of the "towers" forum. Also you can search the archived forum from last year. Just use keywords like "SPFD" and all the posts with that will come up.

[Girlpower05]

What bracing intervals would work best for a division B tower this year?

[kinghong1970]

What bracing intervals would work best for a division B tower this year?

Figuring that out by the competitors would be the nature of any challenges imo.

If we were all given plans and instructions then it would defeat the purpose of such challenges no?

[GhostPants_]

Hello everyone! Hope your season is going well thus far. I recently decided I'd post one of our designs from an invitational last year on YouTube because it was a two-part design, similar to the design mandated by this year's rules. This tower placed first at the invitational with a score of 1493.

https://www.youtube.com/watch?v=5v9I5DDAM8Q

If you are interested, my channel also has our State-winning tower from last year and a few other Science Olympiad-related videos.

Good luck this year, and I hope this video can help!

[dholdgreve]

What bracing intervals would work best for a division B tower this year?

Yes, you have summed up the entire tower competition in one sentence!
The bracing interval is a function of the column density and stiffness. As the column density goes up, the number of bracing tiers can come down (theoretically, anyhow). The lighter the columns, the more bracing will be required.