Designs

[pihi]

Well...I don't know...I think another thing is that I didn't exactly put much effort into the first tower...

[mrsteven]

Well...I don't know...I think another thing is that I didn't exactly put much effort into the first tower...

no offense, not trying to be negative but some tips...
before asking help, try putting some effort into it. If you make a junk built tower with the best designs, its still junk. Don't say it doesnt work unless you did it to the best of ur abilities- then change.
We're totally willing to help but if youre not going to help yourself, then theres nothing we can do- be motivated no ones going to hand you on a platter what to do.

Onwards...
Keep in mind for beginning builders wood is just as important as the pattern design itself. I have a design that I know works well (seen in action several times in slightly varying forms) and added my own twist then comes wood choice. Dimensions and stiffness (sometimes related to density) are the main factors. Decide on dimensions before densities. Then test to find what you need for each stiffness to have a good tower at lowest weight. this is where most teams fail because they arent motivated enough to build a bunch with suble differences in stiffness of pieces (and where I'm still procrastinating although im closely in the ball park... not totally correct yet though).

A little effort goes a long way

[pihi]

I understand that and if I had a little more time, I would experimenting myself. The problem is, I was assigned to do Towers a week and a half before invitationals so I don't exactly have time to spend all my time on one tower and then find out it flukes. Again, I normally would do this all myself but in this case, I have never done the event before and with such a time constraint I had to refer this forum.

[Balsa Man]

You are not going to be able to go from never having built a tower to having a competitive one in a week and a half. What do I mean by competitive? Medal-winning, top 5, probably top 10.

What you may be able to do in that time is get a tower that is in the first tier (meets the construction specs), and that will beat the....."you gotta be kidding" ones you always see.

If I were in your situation, I'd suggest running down to your local hobby store, getting some 1/8th inch square cross section bass wood for legs, some 1/8th balsa for ladders, and some 1/16th balsa for X-bracing. Only go for the minimum 40cm height. 15cm base, 25cm chimney. Take a few hours to make a form- a jig to hold the legs in position so you can glue the ladders and xs to them- make it out of cardboard/posterboard. You need to be careful - and take the time to get it.....pretty darn straight- if its not straight and symmetrical, you'll be wasting your time; the tower off it will fail at very little load. In the base, do a ladder at midpoint of the legs. In the chimney, ladders top and bottom, and two in between, dividing the chimney into 3 sections a bit over 8cm long. If its pretty straight, you'll end up with a weight in the 20=30 gram range, and it might carry 10-12kg- if built decently and straight, might carry full weight.
Good luck

[pihi]

Thank you! I'm not really going for top 5 but more as, I need to do decent with the time I have. I really appreciate your tips

[thsom]

which would be better for a chimney design?
1: (tower on it's side)
I\/\/\/\/\/\/\/\/\I
The bolded ones are diagonals braced every 2 cm, the non-bolded are diagonals braced every 3.5 cm
2: (tower on it's side)
I\/\/\/\/\/\/\/\/\/I
All are diagonals braced every 3 cm.

[flyingwatermelon]

which would be better for a chimney design?
1: (tower on it's side)
I\/\/\/\/\/\/\/\/\I
The bolded ones are diagonals braced every 2 cm, the non-bolded are diagonals braced every 3.5 cm
2: (tower on it's side)
I\/\/\/\/\/\/\/\/\/I
All are diagonals braced every 3 cm.

The second one. It's likely its more efficient and remember that you want equal bracings as much as possible. That way you don't stress one area too much. For example your first tower, you would just be testing the 3.5 cm, but for the second one it would be 3cm, which would likely break at a heavier weight.

[Barker]

I think that thsom does bring up a significant question as to whether
/\/\/\/\/\/\/\/\/\/\/\
If different from
/\/\/\/\/\/\/\/\/\/\/
The difference being the direction of the final members and whether they match or not,
(I can't help wanting to descibe it as being chiral...)
Instead of thsom's where some were unevenly spaced

My initial thoguh would be that the second would be preferable because of how in the first 2 of the 4 members would have a different member pattern as far as how many attatchments there would be. Though my reasoning in this might be flawed int his, any opinions?

[Balsa Man]

I can't tell from the description & diagrams exactly what's going on in the 2 scenarios, but going back to basics:

The legs work as "stacked columns", braced intervals between bracing points (where the bracing locks that point of the leg in space) where the buckling strength in each interval depends on the length of the braced interval. If all braced intervals are the same, the overall leg will have the buckling strength of each of the braced intervals. If there's one or more braced intervals that are longer, they will have lower buckling strength, and the buckling strength of the overall leg will be that of the longer interval(s). Column strength vs length is an inverse square relationship. So, if a leg will hold 4.31kg at a braced interval of 3cm, it would only hold 3.17kg at a 3.5 cm interval

[thsom]

I can't tell from the description & diagrams exactly what's going on in the 2 scenarios, but going back to basics:

The legs work as "stacked columns", braced intervals between bracing points (where the bracing locks that point of the leg in space) where the buckling strength in each interval depends on the length of the braced interval. If all braced intervals are the same, the overall leg will have the buckling strength of each of the braced intervals. If there's one or more braced intervals that are longer, they will have lower buckling strength, and the buckling strength of the overall leg will be that of the longer interval(s). Column strength vs length is an inverse square relationship. So, if a leg will hold 4.31kg at a braced interval of 3cm, it would only hold 3.17kg at a 3.5 cm interval

Got it, your tower is only as strong as it's weakest (or longest in this case) bracing. Thanks!