OK, hearthstone 224, catching up on one of your posts I hadn't responded to:
1. Confirmation- The way you measure buckling strength is the number you get when it starts to stay still, right? It will reach a certain threshold, and that's the number we want? It doesn't matter how far it is bending as long as the bottom is staying still?
Because I have a piece of 1/8x1/8x36 balsa wood that stays still at around 75 grams, and I thought I would roll with that since it is above your number of 60g.
As discussed, yes. If you have 4 sticks that test out at 75gr at 36”, and build with a 1/5 bracing interval, you should be fine. Looking at our inverse square table, legs from those pieces should have a BS of 5,921; that’s a very comfortable/conservative safety factor over the 3,840 force each leg will be seeing at a 15 kg load. That’ll give you some margin to handle ….less than perfect building technique; a good idea for someone who is not an experienced builder.
1a. When we say that the BS of a stick at a braced interval of, oh say 1/3 interval is 2000g (just making it up), would that refer to the strength of the structure after we attach whatever kind of braces we want (say X) and then put another stick next to it? What is that BS referring to?
Yes, because bracing turns a long column into a set of shorter ‘stacked columns’, so the BS of the long, braced column becomes that of the shorter, stacked/braced columns. Don’t understand what you mean about, “then you put another stick next to it.” When the bracing is all installed on the tower, all 4 legs are braced, and have the BS of the braced interval. If you put together/use the table I provided the set of columns for, and look at the values for 1/3 interval bracing for a 51.546cm long leg, you’ll see that a 36” stick, with a tested BS at 36” of 70gr will, when braced at the 1/3 points, provide a BS of 1,989gr (28.42 times the BS at 36”)- pretty close to your 2000 figure.
2. When you state the leg length for the whole thing (C division) is 61.343cm, what is that referring to? And how did you get that number? Basically, a bit of elaboration on "leg length", whatever it is, would be very helpful. It sounds pretty basic but I just want to make sure.
Leg length is….the length of the legs. As described many times previously, the leg length I’m talking about is for a tower that has the legs at the bottom (sitting on the test base) far enough apart to clear the 29cm circle by 3mm on all sides, and is 3mm higher than the minimum height in the rules. The number for the leg length is simple geometry- Pythagorean Theorem; a sqared + b squared = c squared….
3. I'm not sure how I'm going to construct this. Like say I figured the sticks I want to use, and then I make my X braces. But how do I connect I part of it to the other? That is what I don't get. Also, how do I connect part of a tower to the base such that it doesn't make a weak point? Maybe I'm just worrying to far into the future but I'd just like to know the plan for that part.
Sorry, I’m having trouble understanding….what you’re not understanding. In simplest terms, at your braced points- whatever interval you end up using- and the points should be carefully measured and marked on your legs before they’re taped to the jig, ready to put the bracing on to hold the legs together, and brace them- you put ‘ladder’ pieces in between the legs- the ends of the ladder pieces butt tightly up against the inside edges of both legs; the ends will need to be carefully cut at an angle that matches the angle at which the legs slope in. These ladders are what hold the legs together, and brace them into shorter intervals. Then you’ll need some sort of diagonal bracing between each set of ladders, Xs or ‘Z’ bracing. I’ll try to get a detailed description of the ‘ladders and Xs’ approach we use posted later today….
As to ‘how to construct’, a) take some time to look at photos in the image gallery of towers, and b) once you have a jig, it will be easy to see how to construct.
As to ‘connect part of the tower to the base’, as I said earlier, with this year’s rules, there is no/should be no lower/base part, with a thin chimney part extending up from it. You want straight legs, forming a single truncated pyramid- wide enough at the base to clear the 29cm circle, narrow enough at the top to fit under the load block; very simple.
Then your most recent one:
hearthstone224 wrote:It seems like the B division tower has more potential, since I calculated the multipliers for each bracing up to 1/7 for C division, and the highest was only 120.76x in the 1/7th bracing interval compared to like 150x for B division. But this is because of the B leg being shorter, isn't it?
Yes, that's correct- 1/7th of 51+cm is shorter than 1/7th of 61+
Is it fine if I just rounded the way you did, should that be accurate enough?
Yes-- provided multiple decimal places just cause that's whats in the spreadsheet
Also, when we calculate the BS down for let's say 1/7th bracing interval, what will that mean? Does that mean once we brace a stick of length 61.343 at a 1/7th interval and add another stick to hold it, it should be able to hold X grams?
Not sure what you mean "add another stick to hold it" I think I covered this above, but not sure. Bracing connects adjacent legs; with bracing in on all four sides, all legs are braced, and the buckling strengths of the legs are the buckling strength of the equal, short braced intervals
And what is the number 61.343 referring to again? Since at one point the tower will curve outwards, right? To elaborate, the leg refers to the straight part of the "skinny pyramid" design, or the whole leg? It's hard to ask this question.
61.343 is, as stated, the length of the leg(s) of a C-Div tower with 3mm clearance of the 29cm circle at the bottom, and the top supporting the 5cm square load block. I explained where that number comes from. Nothing "curves out"- not the tower, not the legs; the legs are all straight; the 4 legs together form a truncated pyramid- they are connected together by bracing.
And thanks Balsa Man your explanation on the reason why we don't cut down the stick when measuring BS really helped me. I get it now why we don't cut it down, that would be impossible to use then
Yup.
) But yeah, grams? Since if I only bow like 1cm the number will fluctuate and I can't get a reading. Only when I bend it somewhat far (and I'll try to take a picture to post on here so you can judge) the number will stay still..
