17-18 Season: Building during the Summer

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17-18 Season: Building during the Summer

Post by scioly2345 » July 10th, 2017, 4:25 pm

I am a tower builder for division B, and I want to know, what's the best design for the most efficient tower? Xs and Ladders? Zig zags? Starting to build over the summer, and also, what glue should I use? Wood glue is what I used from 15-17. And which would be better, a one or two piece tower? A 16cm by 16cm tower or a 29.cm by 7cm tower? Thanks!!
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Re: 17-18 Season: Building during the Summer

Post by Unome » July 10th, 2017, 6:12 pm

scioly2345 wrote:I am a tower builder for division B, and I want to know, what's the best design for the most efficient tower? Xs and Ladders? Zig zags? Starting to build over the summer, and also, what glue should I use? Wood glue is what I used from 15-17. And which would be better, a one or two piece tower? A 16cm by 16cm tower or a 29.cm by 7cm tower? Thanks!!
Xs and ladders or Xs only are typically the two best designs.

CA glue (cyanoacrylate) is easily the best type. Medium viscosity is easier to use, though I've heard that low viscosity is superior in quality (but it's a small difference).

A one piece tower is better, but that depends on what the 2018 rules allow. I'd recommend building some two-piece towers.

Square base is typically better.
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Re: 17-18 Season: Building during the Summer

Post by Random Human » July 10th, 2017, 7:04 pm

scioly2345 wrote:I am a tower builder for division B, and I want to know, what's the best design for the most efficient tower? Xs and Ladders? Zig zags? Starting to build over the summer, and also, what glue should I use? Wood glue is what I used from 15-17. And which would be better, a one or two piece tower? A 16cm by 16cm tower or a 29.cm by 7cm tower? Thanks!!
Look around in the towers forums... pretty much any and every question is answered there... credits to balsa man
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Re: 17-18 Season: Building during the Summer

Post by Dohnnovan » July 11th, 2017, 4:01 pm

Random Human wrote:Look around in the towers forums... pretty much any and every question is answered there... credits to balsa man

True lol
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Re: 17-18 Season: Building during the Summer

Post by Balsa Man » July 14th, 2017, 9:38 am

Random Human wrote:
scioly2345 wrote:I am a tower builder for division B, and I want to know, what's the best design for the most efficient tower? Xs and Ladders? Zig zags? Starting to build over the summer, and also, what glue should I use? Wood glue is what I used from 15-17. And which would be better, a one or two piece tower? A 16cm by 16cm tower or a 29.cm by 7cm tower? Thanks!!
Look around in the towers forums... pretty much any and every question is answered there... credits to balsa man
Well, first, let me echo Random Human’s guidance. As you can see looking at the Towers forum index, we got to over a hundred pages of posts last season; and easily 50 pages of that provided/provides good, detailed discussion and specific information and data on how to create a good, competitive tower. A number of coaches with years of experience, including me, contributed to that, as did a number of successful builders (active and graduated). There is nothing approaching this ‘book of knowledge’ anywhere else; by finding Scioly, you’ve come to the right place. Key areas covered included…let’s call it the basic underlying physics and engineering (what’s going on with the forces in a loaded tower, how do pieces under loading behave, how do you figure out the forces on various pieces), the properties of wood (how do cross section, length, density affect strength/performance), translating the underlying….science into a structure- an idea/a design into a structure that….works as designed, the engineering process/mindset- how do you get to a good design, and then refine/optimize it to the best performance.

There are a number of us that believe in the importance of getting accurate, and detailed information and understanding out there – to help anyone who wants to learn and understand what it takes to do well. I, and I believe others, have seen, and frankly felt sorry for competitors- students and coaches who obviously … are completely clueless- who show up with a 1000gram tower/structure that breaks at a 5kg load, when the medalists are running 5, 6, 7gram towers carrying full, or close to full 15kg load, and can only conceive those winning structures as something magical and totally mysterious. The whole purpose of S.O. is learning. What are students to do if the coaches and volunteer help- parents and others, for their school, have no idea of how to teach/guide them toward creating a …. respectable structure? Trying to help with that; to help up the level of the playing field for all.

You’re not going to get, here, the absolute, full design and construction detail behind a National medal-winning team’s structure; there is, for sure, a competitive context; we each have, every season, our newest little insights/understandings, new tricks to hopefully win with. But you will get very detailed information on how to end up with a very competitive tower. With so many headings, and pages, and topics getting covered in sections that are different from the section/topic titles, it’s a bit like a treasure hunt to chase down the good info that’s here. But like the X-files, ‘the truth is out there.’ The most important thing you can do this summer is invest the time to find and fully digest the information that’s been developed.
There is a large amount of basic/fundamental information laid out in the first 10 pages of the Towers B/C thread- on page 2, the basic mathematical relationships you need to understand; on page 4, other important basic concepts for design, construction, development of a design; on pages 6 and 7 the value and concept of using a jig/jigs, and info on how to build one, and on pg 8 more good discussion on important basic concepts; page 10 provides good discussion on bracing, and details on implementing the Xs and ladders option. The next 40 pages build on, and get into more detail on the basics laid out in the first 10 pages. A number of the other threads also provide critical/useful info, and a LOT of very detailed discussion on exactly how to do…lots of things, and better understand the underlying theory.

Second, realize/understand, this year’s rules are going to be different from last season, so specific advice is going to have to wait until the rules are out. A key aspect/example of that is your “one piece” vs “two piece” basic configuration of the tower question. The choice is/will be dictated by the rules. Back in 2011/2012 (the last time prior to last year that towers were the structure), the rules required that, above a specified distance above the testing base, the tower had to fit within an 8cm diameter circle, so to meet the specs, you had to go with two very different configurations in upper and lower sections/parts- a/the “two-piece” approach. Last year’s rules had no such constraint, so straight leg “one piece” towers were the optimal way to go, and anyone using a 2-piece approach was just shooting themselves in the foot- creating additional difficulties/challenges, gaining nothing. It is significantly harder to get a precise, symmetrical ‘two piece’ tower built. Given that the typical approach of the rules makers is, in the second year a given structure (towers, bridges, boomilevers) is run, the rules are tweaked to…increase the challenge compared to the first year, a lot of us are suspecting that some form of size constraint above a certain height is likely to re-appear. When this year’s rules are released, there will be detailed information on how to design/build a competitive tower for this season appearing/developing here on this forum.

As to, “16cm x 16cm or 29cm x 7cm” (base dimensions, presumably) question… As with basic shape and configuration, depends on the rules. Last year’s rules gave a 2kg “load credit” if your legs were spread out enough to fit outside a 29cm circle.

Its unknown if the circle bonus will be there in this year’s rules, and if so, what the load credit will be set at. Circle size could change, but I think that’s unlikely. There was a lot of discussion last year as to whether it was “worth it” to build to get the bonus. In the end, it turned out to be a pretty close call, but top towers at Nationals were non-circle bonus ones. Were the load credit to go up a bit, going for the bonus could become an obvious, no-brainer choice. For a square base configuration, a tower meeting the 29cm circle bonus would be at about 21cm x 21cm. There was some discussion last season of the tradeoffs between a square vs rectangular base configuration. As far as I know (and others that watched various tournaments, including Nationals, please chime in/correct if needed) square base configuration performed better than rectangular (for circle bonus and non-circle bonus towers). The issue/the driving factor is the length of bracing down near the bottom. Bracing, regardless of the system/configuration, has to be able to manage both tension and compression forces. Length essentially doesn’t matter for tensile loading, but it matters a lot in handling compression loading. At the same cross section and density, under compression loading (which will cause it to buckle),a piece twice as long as another has only ¼ of the strength. The long lower bracing pieces in a rectangle configuration have to be beefed up in comparison to what will work in a square configuration. Its something that needs to be looked at closely, but my past experience says square is the way to go.

As to glue, as Unome notes (and as reflected in last season’s posts), CA – super glue is in most folks opinion the way to go. Thin, medium, thick- depends on preference, and specific type of joint.

What bracing configuration is optimal? Lots of discussion around this last season, and going back years; no quantitative, as in ….all calculated out, hard “fully engineered” answer. Last season, I laid out in a series of posts a detailed engineering analysis for a ladders and Xs approach, noting I wasn’t sure it was the absolute lightest way to go. Based on input from a number of folk running an all Xs configuration, for Nationals, both the C and B teams I was working with switched and went with all Xs (and improved our score from State, and placed inside the top 15 at Nats). One of the key things I hope to do this season is get/develop a better engineering handle on how an all Xs approach really works, and how to quantitatively design it. I will certainly be sharing what we find.

Bracing works to do two things. The first is to turn the legs into a set of short, ‘stacked columns.’ The second is to provide overall structural….integrity/rigidity; to keep the structure as a whole from twisting/bending under load. A good design has to do both things. Both all Xs, and Xs and ladders are symmetrical in the sense they work to resist structural twisting equally in both directions. Not all ‘zig-zag’ arrangements do that. Again, if anyone saw a zig-zag bracing configuration that was really competitive (medaling at State/Nationals, please say something- I didn’t see, or hear of any examples.
Bracing involves/is related to a very fundamental design “tradeoff.” You can get to the buckling strength you need in the legs by either heavy, stiff legs with minimal bracing (i.e. wide bracing intervals), or light floppy legs with a tighter/closer bracing interval. Somewhere in that spectrum is the optimum- the combination that gets you to the lightest structure that will just barely carry full load. See notes on how to do that evaluation further down in this post.

Last, a quick summary of five things that, IMHO, really matter in how you approach towers, if you really want to be “competitive.” “Competitive” for purposes of this discussion, is a pretty subjective term. The level of competitiveness varies a lot from State to State. So let’s say competitive = in all but the few really competitive States, a reasonable chance of medaling at State….

Its all about learning and applying the engineering process- learning and applying science. As you’ll learn as you study the information already in this forum, there are a lot of variables…’at work’- factors that if/as you change something, it has an effect on how efficient your tower ends up, how well it scores. Many of those variables are interactive- changes in one….aspect/variable drive/create changes in another or others. So, the fundamental concept- the path to competitiveness – is control of variables.

First thing is learning and understanding of the basics-
It requires coming to a real understanding of the underlying science; how things work, understanding and calculating forces involved and strengths of various wood options, the mathematical relationships that allow you to understand how things work, and calculate and predict how changes in shape and materials will affect structure performance. This takes research, study, ‘playing with the numbers’, setting up notes/spreadsheets to see and calculate how changing variables changes the…outcome.

A key basic understanding, discussed at length in many forum posts, is ‘buckling strength.’ This needs to be understood for any pieces that come under compression loading – where the ends are being pushed together. Legs are the primary components under such loading. A stick, where a force is being applied along its axis, will at some load fail by buckling- the middle will suddenly bow outward. If the force/load that induced buckling to start is maintained, the bowing will increase rapidly until it fails/breaks

Second thing/concept is “shape control”-
Its pretty easy to draw up/define a “shape” – set of lines (whether drawn by hand, or in CAD or other drawing program), with these lines defining the orientation/alignment of legs and bracing pieces in 3-dimensional space. These lines are defined by a) the constraints set out in the rules, and b) the….way things work- the forces, strengths needed to handle those forces, etc. Its harder to get to a correct/good, ‘optimal’ answer on how those lines (tower pieces) should be configures/arranged. It’s a big challenge to turn that “perfect” design shape/configuration into a real 3-D structure that creates the design.

You need to control the ‘shape’ variable in two ways, for two reasons. First reason, the shape you create needs to be symmetrical, and precise. Any calculation of forces and strengths comes from/is done from… a theoretical, symmetrical shape. As an example, say leg angle is 12.60 degrees from vertical, the legs are exactly the same length, and hence force, under a 15kg tower load, on each leg is 3.88kg. This comes from 3.75kg, which is ¼ of 15kg (load equally distributed on the 4 legs, times 1.0248, which is 1/the cosine of 12.60 degrees). If the legs were vertical, under a 15kg load, each would see/be carrying 3.75kg. When they are angled, leaning in, the force they see (at a given load) goes up as the lean-in angle increases, and that increase is proportional to 1/cosine of the lean-in angle from vertical; 3.75 times 1.0248 = 3.88..

Second ‘precision’ example; if, for instance, your base is not perfectly square, and the four legs are not 90 degrees apart all the way to the top legs, and leg lengths are slightly different, the load the individual legs see can/will vary significantly. The whole idea in a competitive design is pushing the limits- where each piece of wood is the lightest that can/will carry its design load. Any structure will fail at the weakest link, so if the legs are the same strength, but are not seeing equal loading, the disproportionally loaded leg/legs will fail prematurely.

Second reason, if you are not controlling the shape (that is, keeping it exactly the same) for each build, you have no way of evaluating changes you make in refining/optimizing your design. Say you test a build, and it fails at 10kg load, so you do a new build with, say a 10% increase in leg density/strength. If the shape/leg alignment is exactly the same (and everything else is the same), you’ll see an increase in tower strength/score proportional to the increased leg strength. However, if the shape/leg alignment is different, and as a result a leg is disproportionately loaded, it might fail at…say, a 9kg tower load, masking/hiding an actual increase in tower strength. You need to be able to change just one variable (at a time) to understand the effect of the change. Otherwise, you’re shooting in the dark/just running in circles.

You’ll see a fair amount of advice- last season, and over the years, that the way to get to a “good” tower/structure is to just build and break a lot- if one design doesn’t do well, build something different. It is true that your building skills will improve the more you build- precision of cuts, minimizing glue use/weight, reducing build time. However, if you don’t control the variables- change/test/evaluate changes one at a time – with an understanding of what you’re changing and why, you are just flat out wasting time. My take (and experience) is that putting time and energy in the ‘up-front’ steps- good design engineering analysis, creating really good tooling/jigs to control shape, and…intelligent, effective testing allows you to minimize the number of builds needed. The B-team I worked with last season that placed 13th at Nationals (competed at Regional and State tournaments- no invitationals) built 6 towers.

You’ll see a lot of discussion (and detailed instructions, and some pictures) last season about “jigs.” A jig (or set of jigs) is a way- a tool you build, to align the pieces for building the tower. There are a lot of ways to design/implement a jig. You want it as symmetrical and precise as you can get to. The limitations are time, money, tool availability, and your proficiency at precisely ‘building things.’ I deeply believe that a substantial portion of the total time you invest in the event should be directed to creating a good precise jig, or jigs. It will pay off big-time. You want to also think about jigs/tooling to guide/assist …other construction operations, e.g., cutting pieces to the exact same length, getting end cut angles exactly the same, etc.

Third thing is “wood control” –
Both for getting to a….design starting point (cross section dimensions and density for all the pieces that should have you in the ballpark for strength needed) , and for subsequent refinement/development- getting to the very lightest pieces that will just carry the loading they see at/near full tower load, you need to really understand just how variable balsa is; how that variability works, and how you can measure and control that variability, and actually get to the lightest pieces that just barely have the strength needed/your design strength. Again, there’s a lot of discussion of this whole subject throughout last season- critical to understand. Balsa exists/comes in a VERY wide range of densities. At a minimum, you need to know/track densities (weights) of any pieces you use; higher density will generally get you higher strength. However, its important to understand that because it is grown, not manufactured, that there is significant variability around the….trend line of increasing strength with increasing density. That trend line, btw, shows that if you double the density, strength goes up by around 2.5X. But, if you look at a number/bunch of sticks at the same density, say 1.5gr, 36”, 1/8”x1/8”, while the median buckling strength at 36” will be around 40 grams, a few may be as low as close to 30 grams, and a few may be as high as 50grams. Again, what you’re looking for to really optimize design – to get really high performance, is those statistical outliers- sticks that meet your design buckling strength, but are the very lightest ones that do so. Finding/getting such ‘special’ sticks is constrained by cost; the more sticks you have/get to sort through, the better your odds of getting a few really ‘high performance’ ones.

There are lots of… units that are sometimes used/can be used to express/evaluate density of balsa; pounds per cubic foot, specific gravity, grams per cubic centimeter, etc. I’ve found it very useful/helpful to work with/use ‘grams per 36 inches.’ Among other things, it makes it really easy to calculate structure weight, and calculate/evaluate potential trade-offs in wood density for various pieces.

Fourth thing is being able to quantitatively evaluate tradeoffs-
As suggested/reflected in the discussion above, there are a lot of options and tradeoffs to be considered, and that play into figuring out what is an optimal design, and how to actually build it. One of the most helpful tools is a set of well thought out spreadsheets. There is detailed discussion in past posts on how to do this.

Two important/specific examples-
-A tower weight estimating sheet, where you can see how tower weight looks considering design options/tradeoffs. As noted above, the big tradeoff to be evaluated is that spectrum between very stiff, heavy legs with minimal bracing (wide bracing interval), and light, relatively floppy legs with tighter bracing interval. The basic idea is to set up a sheet with legs, bracing (ladders, Xs (orZs) and other, like tension strap at the bottom) sections, and estimated glue sections, with total tower weight sums at the bottom.
For each row, have space to enter name, number,spec notes (e.g. “using 1/8 at 1/5g/36”), length(in cm), density info- in gr/cm, and weight (which =length x gr/cm). Set up one initial master sheet, make copies, fill in values for a range of alternatives.

-A wood inventory tracking sheet, so once you’ve measured weight/strength of your ‘lumber’, you can lay your hands on pieces you want to work with. You’ll also want a marking system to go with this- felt-tip colored markers.

And fifth thing is commitment -
Being ‘competitive’ in any of the building events does not, and will not, happen if you’re not committed to putting substantial time and effort in, and sustaining that through the season, and through the sequential stages of understanding the science, designing, building, and optimizing performance. Certainly true for towers. If it was easy, everyone would be… a champion.
The first commitment hurdle is study- reading, re-reading, thinking about available information.
The second is planning- getting a game plan together, getting tools and materials, working through design basics, evaluating trade-offs/options in design
The third is ‘taking shape control’- actually creating the tools- e.g., jig(s) you need to build with- and doing it precisely/carefully
The fourth is money- you will not be able to build a “competitive” tower with….$20 worth of whatever balsa your local hobby store happens to have on hand.
The last is time management- thinking through and understanding the steps needed, and making and allowing the time to work through them- not waiting till the last minute and scrambling to catch up.

Lots to think about……
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Re: 17-18 Season: Building during the Summer

Post by Random Human » July 18th, 2017, 10:15 am

Hey I think rules are out.... I'm not sure though
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Re: 17-18 Season: Building during the Summer

Post by SOPomo » July 18th, 2017, 10:29 am

Random Human wrote:Hey I think rules are out.... I'm not sure though
Only at SOSI, or any coaching clinics that have existed so far (California has a couple I think). Official rules are released at the beginning of September.

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Re: 17-18 Season: Building during the Summer

Post by Random Human » July 18th, 2017, 10:48 am

SOPomo wrote:
Random Human wrote:Hey I think rules are out.... I'm not sure though
Only at SOSI, or any coaching clinics that have existed so far (California has a couple I think). Official rules are released at the beginning of September.
Can you draft an outline of like the changes.. I'm curious to hear

Is it the 2 part design? Anything?
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Re: 17-18 Season: Building during the Summer

Post by Random Human » July 18th, 2017, 11:22 am

The only new rule is a 2 part design... intresting...
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Re: 17-18 Season: Building during the Summer

Post by SOPomo » July 18th, 2017, 12:33 pm

Random Human wrote:
SOPomo wrote:
Random Human wrote:Hey I think rules are out.... I'm not sure though
Only at SOSI, or any coaching clinics that have existed so far (California has a couple I think). Official rules are released at the beginning of September.
Can you draft an outline of like the changes.. I'm curious to hear

Is it the 2 part design? Anything?
I've been asked not to do my SOSI AMA thread so I can't/won't release the stuff we talk about to be respectful of that. There are a number of changes and our session is this afternoon to fine tune it all.

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