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Hello all. Last year my partner and I won bridges in our state (NC) with a score of about 2300. Not in competition our best was around 2500, which is not bad. This year we are having some real trouble with towers. We haven't gotten above 800 efficiency, which we consider abysmal. Our main concern is weight. With most being above or just below 10g. How can we cut that down? and is the 29cm bonus worth the additional weight. Any advice would be appreciated.

LWilde14 wrote:Hello all. Last year my partner and I won bridges in our state (NC) with a score of about 2300. Not in competition our best was around 2500, which is not bad. This year we are having some real trouble with towers. We haven't gotten above 800 efficiency, which we consider abysmal. Our main concern is weight. With most being above or just below 10g. How can we cut that down? and is the 29cm bonus worth the additional weight. Any advice would be appreciated.

Consensus seems to be that the bonus is worth it; see Balsa Man's posts on it in the first ten pages or so of this thread.

(I just popped in to answer that specific question)

Hmmm, with a 10 gr tower scoring around 800, that's failing at an 8kg load.
The first question in my mind (and direction to do some work/analysis in) would be why its not carrying close to full load.

10 gr tower with good symmetry/precision (i.e., built on a reasonably decent jig), and specs on wood density and bracing intervals that have been posted should comfortably carry 15kg, or very close. And those specs are for a tower meeting the 29cm bonus. Spreading the legs out to get to the bonus is not going to add very much weight, and will kick score significantly. That same 10gr tower carrying 8kg would score 1000 w/ bonus.

This all makes me wonder if there's some...key design flaw/issue that you haven't figured out.
If you'd like to provide a description, might be able to provide more specific suggestions....
Like leg densities/stick weights from which the legs are cut, bracing interval used, bracing system (ladders and Xs, Xs only, ladders and Z bracing, and specs on the wood used in bracing...

So what I have is legs of 3/32 by 3/32 balsa. They each weigh about .6 grams at 36". I used the finger on the scale method to find out their buckling strength- around 20g. So, would bracing at 1/12 work for these dimensions? Division C tower with bonus

to add on, my bracing design is X with ladders

Complexity wrote:to add on, my bracing design is X with ladders

Okay, I went back to page ten of forums. With these dimensions, I (tried) to calculate buckling strength and got a number of 6389. Took several times to understand. If 3840 is the force on a leg... I think I might have messed up somewhere, because this number appears too high

Actually, with that buckling strength, bracing at 1/7 intervals with ladders and Xs should work. What interval have you been using?

Balsa Man wrote:Actually, with that buckling strength, bracing at 1/7 intervals with ladders and Xs should work. What interval have you been using?

Every 1/12 of the tower. At every six inches. The buckling strength is 20 for a piece. It is 15 for the rest, so less. My legs are very light, so I will take the floppy leg more bracing approach.

Complexity wrote:

Balsa Man wrote:Actually, with that buckling strength, bracing at 1/7 intervals with ladders and Xs should work. What interval have you been using?

Every 1/12 of the tower. At every six inches. The buckling strength is 20 for a piece. It is 15 for the rest, so less. My legs are very light, so I will take the floppy leg more bracing approach.

If you say that 1/7 will work, then I think I will reconsider my bracing interval. I want a little more to be safe, maybe 1/10. 1/7 worked with 20 buckling strength, but would more would probably be needed since now they all show 15.
Made the cutting jig

Complexity wrote:

Complexity wrote:

Balsa Man wrote:Actually, with that buckling strength, bracing at 1/7 intervals with ladders and Xs should work. What interval have you been using?

Every 1/12 of the tower. At every six inches. The buckling strength is 20 for a piece. It is 15 for the rest, so less. My legs are very light, so I will take the floppy leg more bracing approach.

If you say that 1/7 will work, then I think I will reconsider my bracing interval. I want a little more to be safe, maybe 1/10. 1/7 worked with 20 buckling strength, but would more would probably be needed since now they all show 15.
Made the cutting jig

1/7 with be ok, you could actually probably even use 1/16 balsa sticks, that would reduce your tower weight as well.