Towers B/C

[random-username]

Thanks Balsa Man! I've read past conversations, and am still working my way up to now. I saw that you recommended going for the bonus, and that the tower with a square base had to span at least 20.9cm, 21cm on one side. How would this work? The rules said the tower could not be supported inside the circle, but part of the base would be touching the testing base inside the circle. How could I work around this? Before I built a 30x30 cm square base to get the bonus, but the score wasn't very good.
Another topic, what density balsa would be best? I've been buying wood from specialized balsa, and have gotten 3/16x3/16 wood in extra light and light. I have also purchased 1/8th wood in extra light, but I had trouble with the joints sticking together. I'm using Gorilla super glue, but I think I might try Zap a Gap if that continues to be a problem.
I'm division B by the way, our team is going to states in late April.

[Balsa Man]

Thanks Balsa Man! I've read past conversations, and am still working my way up to now. I saw that you recommended going for the bonus, and that the tower with a square base had to span at least 20.9cm, 21cm on one side. How would this work? The rules said the tower could not be supported inside the circle, but part of the base would be touching the testing base inside the circle. How could I work around this? Before I built a 30x30 cm square base to get the bonus, but the score wasn't very good.
Another topic, what density balsa would be best? I've been buying wood from specialized balsa, and have gotten 3/16x3/16 wood in extra light and light. I have also purchased 1/8th wood in extra light, but I had trouble with the joints sticking together. I'm using Gorilla super glue, but I think I might try Zap a Gap if that continues to be a problem.
I'm division B by the way, our team is going to states in late April.

On circle; draw it out- a 21cm square, and 29cm circle on same center, you'll see the corners of the square are outside the circle. a squared plus b squared = c squared. The diagonal of a 21cm square is 29.69; each opposite pair of legs clear by 3mm on each side- and there's nothing touching base/base plane in between
On wood: I've laid out in.....complete detail the numbers for 1/8" wood. I've provided the exact methodology to calculate, from measured buckling strength, the needed bracing interval for a given leg strength. So you can calculate for 3/16.
Digest the info, work with it, and let me know if you run into something you can't figure out.

[Balsa Man]

The tower I described yesterday held 14350 grams. Today's is the same but with a single 1/16 x 1/16 inch ladder at a 1/2 interval. So I don't know if it's worth it.

Also, if the ladders break because of their low density, won't that cause sudden stress on the tower and cause it to fail?

Curious- what's your tower weight (holding 14350?
If a ladder breaks, it will be because it had a force on it stronger than it could hold against; that breaking is/will be the initial failure. Failure always starts at one point, the weakest point/link, and then (almost instantaneously) other things go.
Good luck, looking forward to hearing how it goes.

Well, I have my latest tower finally done with Regionals today. I followed the same design as last time, except I used 1.3g wood instead of 0.8g wood at the top. Hoping I don't have that same failure point this time.

Likewise, good luck, and looking forward to a report.

Unfortunately, I only got 1200g... I did a stupid.

For all of my towers, I haven't been doing compression members at the very bottom since I didn't think to make them 1-2mm from the base and meet the bonus.
I think the ones where the top failed were actually where the bottom failed in the same way, and the block broke through. I'm going to try repeating the design, this time with braces at the bottom, since the top was fully intact.

Sorry, I'm not following:
The leg ends at the bottom have force pulling them out/apart; I've talked about a bottom "band", 1, 2, 3mm off the base- TENSION strips to hold them against outward movement.
Putting bottom band pieces "1-2mm from the base" has nothing to do with meeting/not meeting circle bonus; that's determined by how far apart the legs are....
At the top, opposite is the case (legs pushing inward/together; there ladder between them, acting in compression holds them apart.

[Tesel]

Sorry, I'm not following:
The leg ends at the bottom have force pulling them out/apart; I've talked about a bottom "band", 1, 2, 3mm off the base- TENSION strips to hold them against outward movement.
Putting bottom band pieces "1-2mm from the base" has nothing to do with meeting/not meeting circle bonus; that's determined by how far apart the legs are....
At the top, opposite is the case (legs pushing inward/together; there ladder between them, acting in compression holds them apart.

I'm sorry, that was a confusing post.

Unfortunately, I haven't been able to run any of my towers since Regionals only runs 5 hours and I do 5 study events.
My partners said that once the loading block was applied, the 1/64 members immediately started to bend at the bottom. The top of the tower stayed intact, while the bottom broke.
The supervisor suggested putting a compression member about 1-2mm off the base, which I tend to agree with - I don't know how, but if the 1/64 members were bending, that implies that they were taking too much tension forces. I hadn't even thought about that, I immediately assumed that compression members at the very bottom wouldn't be possible and assumed that they would be touching the base, that is very obviously false which is what I am trying to say.

I've got 6 weeks until states, so I will go ahead and try both, but it seems like something I was doing was placing compression at the bottom. I will build one design that adds a compression member at the bottom and another the buffs up the tension members at the bottom, and see which does better. Hopefully I can bump this up to a 2000 to compete at States.

[random-username]

Thanks Balsa Man! I've read past conversations, and am still working my way up to now. I saw that you recommended going for the bonus, and that the tower with a square base had to span at least 20.9cm, 21cm on one side. How would this work? The rules said the tower could not be supported inside the circle, but part of the base would be touching the testing base inside the circle. How could I work around this? Before I built a 30x30 cm square base to get the bonus, but the score wasn't very good.
Another topic, what density balsa would be best? I've been buying wood from specialized balsa, and have gotten 3/16x3/16 wood in extra light and light. I have also purchased 1/8th wood in extra light, but I had trouble with the joints sticking together. I'm using Gorilla super glue, but I think I might try Zap a Gap if that continues to be a problem.
I'm division B by the way, our team is going to states in late April.

On circle; draw it out- a 21cm square, and 29cm circle on same center, you'll see the corners of the square are outside the circle. a squared plus b squared = c squared. The diagonal of a 21cm square is 29.69; each opposite pair of legs clear by 3mm on each side- and there's nothing touching base/base plane in between
On wood: I've laid out in.....complete detail the numbers for 1/8" wood. I've provided the exact methodology to calculate, from measured buckling strength, the needed bracing interval for a given leg strength. So you can calculate for 3/16.
Digest the info, work with it, and let me know if you run into something you can't figure out.

I've drawn it out, but the base seems to still be touching the testing base inside the circle: https://lh3.googleusercontent.com/-z5a8 ... -03-19.png
How does this work? Is the base of the tower horizontal? Or is it just on four points (which would not make very much sense?)? How would the tower not be supported within the circle? I'm picturing a basic tower frame like this: https://lh3.googleusercontent.com/-Mtqv ... -03-19.png
I'm probably thinking about this the wrong way sorry!!

[dhdarren]

Thanks Balsa Man! I've read past conversations, and am still working my way up to now. I saw that you recommended going for the bonus, and that the tower with a square base had to span at least 20.9cm, 21cm on one side. How would this work? The rules said the tower could not be supported inside the circle, but part of the base would be touching the testing base inside the circle. How could I work around this? Before I built a 30x30 cm square base to get the bonus, but the score wasn't very good.
Another topic, what density balsa would be best? I've been buying wood from specialized balsa, and have gotten 3/16x3/16 wood in extra light and light. I have also purchased 1/8th wood in extra light, but I had trouble with the joints sticking together. I'm using Gorilla super glue, but I think I might try Zap a Gap if that continues to be a problem.
I'm division B by the way, our team is going to states in late April.

On circle; draw it out- a 21cm square, and 29cm circle on same center, you'll see the corners of the square are outside the circle. a squared plus b squared = c squared. The diagonal of a 21cm square is 29.69; each opposite pair of legs clear by 3mm on each side- and there's nothing touching base/base plane in between
On wood: I've laid out in.....complete detail the numbers for 1/8" wood. I've provided the exact methodology to calculate, from measured buckling strength, the needed bracing interval for a given leg strength. So you can calculate for 3/16.
Digest the info, work with it, and let me know if you run into something you can't figure out.

I've drawn it out, but the base seems to still be touching the testing base inside the circle: https://lh3.googleusercontent.com/-z5a8 ... -03-19.png
How does this work? Is the base of the tower horizontal? Or is it just on four points (which would not make very much sense?)? How would the tower not be supported within the circle? I'm picturing a basic tower frame like this: https://lh3.googleusercontent.com/-Mtqv ... -03-19.png
I'm probably thinking about this the wrong way sorry!!

I'll jump in;

I'm assuming this is regarding the bonus for the 29cm circle? The rules say that only the parts touching the base need to be outside of the circle. Therefore, if your tower sits on the four legs (the four corners of the base of the tower), if will sit outside of the circle, as you drew in your first diagram. But, I think you are imagining your tower as one that has the 4 edges of the base of the tower contacting the ground. Indeed, if you had pieces of balsa wood forming a square on the bottom of your tower, then you would not meet the bonus, since they are touching the base within the circle. But if it elevated upon the four legs, then the only points of contact with the testing surface are those four legs, thus qualifying for the bonus since the legs sit outside the circle.

[Balsa Man]

On circle; draw it out- a 21cm square, and 29cm circle on same center, you'll see the corners of the square are outside the circle. a squared plus b squared = c squared. The diagonal of a 21cm square is 29.69; each opposite pair of legs clear by 3mm on each side- and there's nothing touching base/base plane in between
On wood: I've laid out in.....complete detail the numbers for 1/8" wood. I've provided the exact methodology to calculate, from measured buckling strength, the needed bracing interval for a given leg strength. So you can calculate for 3/16.
Digest the info, work with it, and let me know if you run into something you can't figure out.

I've drawn it out, but the base seems to still be touching the testing base inside the circle: https://lh3.googleusercontent.com/-z5a8 ... -03-19.png
How does this work? Is the base of the tower horizontal? Or is it just on four points (which would not make very much sense?)? How would the tower not be supported within the circle? I'm picturing a basic tower frame like this: https://lh3.googleusercontent.com/-Mtqv ... -03-19.png
I'm probably thinking about this the wrong way sorry!!

I'll jump in;

I'm assuming this is regarding the bonus for the 29cm circle? The rules say that only the parts touching the base need to be outside of the circle. Therefore, if your tower sits on the four legs (the four corners of the base of the tower), if will sit outside of the circle, as you drew in your first diagram. But, I think you are imagining your tower as one that has the 4 edges of the base of the tower contacting the ground. Indeed, if you had pieces of balsa wood forming a square on the bottom of your tower, then you would not meet the bonus, since they are touching the base within the circle. But if it elevated upon the four legs, then the only points of contact with the testing surface are those four legs, thus qualifying for the bonus since the legs sit outside the circle.

Thanks-
Absolutely correct.
As discussed, you may want a "tension band" around the bottom- just put it 2-3mm above the base, so its at the bottom, but doesn't touch the base

[Balsa Man]

Sorry, I'm not following:
The leg ends at the bottom have force pulling them out/apart; I've talked about a bottom "band", 1, 2, 3mm off the base- TENSION strips to hold them against outward movement.
Putting bottom band pieces "1-2mm from the base" has nothing to do with meeting/not meeting circle bonus; that's determined by how far apart the legs are....
At the top, opposite is the case (legs pushing inward/together; there ladder between them, acting in compression holds them apart.

I'm sorry, that was a confusing post.

Unfortunately, I haven't been able to run any of my towers since Regionals only runs 5 hours and I do 5 study events.
My partners said that once the loading block was applied, the 1/64 members immediately started to bend at the bottom. The top of the tower stayed intact, while the bottom broke.
The supervisor suggested putting a compression member about 1-2mm off the base, which I tend to agree with - I don't know how, but if the 1/64 members were bending, that implies that they were taking too much tension forces. I hadn't even thought about that, I immediately assumed that compression members at the very bottom wouldn't be possible and assumed that they would be touching the base, that is very obviously false which is what I am trying to say.

I've got 6 weeks until states, so I will go ahead and try both, but it seems like something I was doing was placing compression at the bottom. I will build one design that adds a compression member at the bottom and another the buffs up the tension members at the bottom, and see which does better. Hopefully I can bump this up to a 2000 to compete at States.

No problem.
No offense intended, but putting a compression member/brace at/near the bottom is wrong. As discussed, the legs, at the bottom, are being forced apart, because they're at an angle, with a vertical load on top; that's just absolutely how it is; the physics of the shape.
Strips seen bending; the bend is not/cannot be compression bending them; think about it- hold at each end and pull them, and they're straight. Push very slightly, and with almost no movement of your hands together, and boink, they visibly bend.
What you were seeing is coming from distortion of the bottom trapezoid- the one, looking at one adjacent pairs of legs, formed by bottom ends, and the first set of braced points, the first ladder. If any of those 4 points shift laterally, one X tightens, one loosens (bends). Coming from either X- strips not being put on properly tensioned, or leg bottom(s) starting to slip outward, or bottom and not being 'finished' properly- sanding/checking/sanding, etc until all 4 tops in full contact with the block, and all 4 bottoms in full contact with the base. If one leg is a hair long or short, load is unequal on legs, and whole tower shape has to adjust. A few thousandths of an inch of movement of anchor point of X-strip will bow it.
Hope this helps.

[dholdgreve]

If there is no ladder at the second node from the table, it is possible hat the columns could be deflecting in toward the center of the column. If this is the case, it will result in making the first tier of X braces look like they are bowing and longer than they should be... As we have discussed many times in the past, X braces are way stronger in tension than in compression. If the columns are indeed bowing in, there is no resistance offered by the X's... The key is to figure out a way to make the columns deflect outward instead of inward, so the bracing can do its job.

[random-username]

I've drawn it out, but the base seems to still be touching the testing base inside the circle: https://lh3.googleusercontent.com/-z5a8 ... -03-19.png
How does this work? Is the base of the tower horizontal? Or is it just on four points (which would not make very much sense?)? How would the tower not be supported within the circle? I'm picturing a basic tower frame like this: https://lh3.googleusercontent.com/-Mtqv ... -03-19.png
I'm probably thinking about this the wrong way sorry!!

I'll jump in;

I'm assuming this is regarding the bonus for the 29cm circle? The rules say that only the parts touching the base need to be outside of the circle. Therefore, if your tower sits on the four legs (the four corners of the base of the tower), if will sit outside of the circle, as you drew in your first diagram. But, I think you are imagining your tower as one that has the 4 edges of the base of the tower contacting the ground. Indeed, if you had pieces of balsa wood forming a square on the bottom of your tower, then you would not meet the bonus, since they are touching the base within the circle. But if it elevated upon the four legs, then the only points of contact with the testing surface are those four legs, thus qualifying for the bonus since the legs sit outside the circle.

Thanks-
Absolutely correct.
As discussed, you may want a "tension band" around the bottom- just put it 2-3mm above the base, so its at the bottom, but doesn't touch the base

Ohhhh! I get it now! I had not thought about doing that before! Thanks so much