Towers B/C

[Balsa Man]

thank you for your input. That is what I was thinking, but I was not sure. I have heard many different outcomes from the X's only design and I am trying it out for myself.

Just for clarification- discussed previously, but to make sure you consider.
At the top, there is a force pushing the top ends of the legs in toward each other; on the order of 1-1.5kg. You have to have pieces in resisting that force; ladder pieces, butt jointed between the legs, with their top surface just a hair (a mm or two) below the leg top ends.

[musicalwhang]

Hey guys, here's my 2nd tower attempt before states. This was my last tower before moving on to build my final states competing tower.
On my first attempt, I had about a 9 gram tower that held ~6 kgs. This attempt, someone recommended that I used butt joints for the ladders on my 5 interval tower. I did this and it came in at ~7.4 grams. This tower held around 5-6 kg and didn't see much improvement from the previous tower. However, the places of failure were drastically different this time. I noticed that the bottom of the leg gave out first instead of the top. Going into my last tower, what should I focus on to get my score up? Thanks guys.
Video: https://drive.google.com/file/d/0B1BYt2 ... sp=sharing
Aftermath: https://drive.google.com/file/d/0B1BYt2 ... sp=sharing

[musicalwhang]

Here all the scores from my state, North Carolina.

DIVISION B
Results from 234 teams across the state
Efficiency 1st- 2,118.6
Efficiency 5th- 1,245.3
Efficiency 10th- 839.0
8 Teams with efficiencies above 1,000

DIVISION C
Results from 223 teams across the state
Efficiency 1st- 1,759.8
Efficiency 5th- 1,375.0
Efficiency 10th- 1,163.0
13 teams with efficiencies above 1,000

[Unome]

Here all the scores from my state, North Carolina.

DIVISION B
Results from 234 teams across the state
Efficiency 1st- 2,118.6
Efficiency 5th- 1,245.3
Efficiency 10th- 839.0
8 Teams with efficiencies above 1,000

DIVISION C
Results from 223 teams across the state
Efficiency 1st- 1,759.8
Efficiency 5th- 1,375.0
Efficiency 10th- 1,163.0
13 teams with efficiencies above 1,000

Do they compile scores from regions and distribute them? That's pretty cool.

[Balsa Man]

Hey guys, here's my 2nd tower attempt before states. This was my last tower before moving on to build my final states competing tower.
On my first attempt, I had about a 9 gram tower that held ~6 kgs. This attempt, someone recommended that I used butt joints for the ladders on my 5 interval tower. I did this and it came in at ~7.4 grams. This tower held around 5-6 kg and didn't see much improvement from the previous tower. However, the places of failure were drastically different this time. I noticed that the bottom of the leg gave out first instead of the top. Going into my last tower, what should I focus on to get my score up? Thanks guys.
Video: https://drive.google.com/file/d/0B1BYt2 ... sp=sharing
Aftermath: https://drive.google.com/file/d/0B1BYt2 ... sp=sharing

It's hard to tell for sure, but what I think I see in the video is a tension failure in your bottom '[strap'- the pieces right at the bottom, that need to be there to hold the bottom ends of the legs together; keep them from pushing apart. It looks like you butt jointed them like your ladders. Those bottom pieces aren't really ladders. The ladders above work under compression, to keep the legs from buckling inward toward each other, and the Xs work in tension. At the bottom, its all tension. Butt joints have virtually no strength under tension. Looking at the aftermath photo, it looks like the bottom piece let go between the center/closest to the camera leg, and the leg to the right. That led to the leg end moving out, and a buckling failure in the leg.
If you lap joint the bottom pieces (and make sure they're strong enough) should work better. Looks like you're using 1/16 for all the brace pieces. To work at the bottom, you'll probably need 1/16 at 0.4, maybe 0.5gr/36". 1/16 x 1/32 at 0.3, 0.4 would save a little weight, and get needed strength.

[random-username]

If you were to build a tower with just x's, would you make the braces attached with butt joints or lap joints? It seems that the goal in making just x brace towers is to make them light, so would a 1/8 leg and 1/16 x brace using lap joints work?

[Unome]

If you were to build a tower with just x's, would you make the braces attached with butt joints or lap joints? It seems that the goal in making just x brace towers is to make them light, so would a 1/8 leg and 1/16 x brace using lap joints work?

I can't comment on the rest, but since the purpose of X's is to resist tension, you would want them to be lap joints.

[Balsa Man]

If you were to build a tower with just x's, would you make the braces attached with butt joints or lap joints? It seems that the goal in making just x brace towers is to make them light, so would a 1/8 leg and 1/16 x brace using lap joints work?

I can't comment on the rest, but since the purpose of X's is to resist tension, you would want them to be lap joints.

Ah, but in an Xs only configuration, they have to handle both tension and compression....

[MIScioly]

I feel like the X's and ladders is a better and easier design, but X's only is the only way to make a super light tower scoring 2500+.

[Raleway]

I feel like the X's and ladders is a better and easier design, but X's only is the only way to make a super light tower scoring 2500+.

That's just build quality If you build a perfect tower with perfect cutting, gluing, and angles you would get a tension only tower that wouldn't bow inwards and would only require tension bracing (I think?) Every tower I've seen 2800+ or 3000+ are purely lap joints for tension members. However, do heed these people building these amazing towers are either using a well built precise jig and/or have years and years of experience choosing wood, designing, and building.