Designs

[thsom]

I agree with the apparent difficulty building, but that depends on how you're doing your jigging.
One of the advantages of thin strip Xs is you don't have the bowing you get with, say, 1/16th square Xs. That bowing means there's a tiny bit of "excess length- if the leg starts to bow out at attachment point, it will be able to pull the bowed X out a tiny bit, which may be enough for the leg bowing to "happen"- to go into column failure. Pre-tensioned strips allow essentially no motion.
You mentioned glueing Xs where they cross- you don't want to do that.

Really, why? I have always had success with gluing where the x's cross? How does this detriment the tower?

[noobforce]

I agree with the apparent difficulty building, but that depends on how you're doing your jigging.
One of the advantages of thin strip Xs is you don't have the bowing you get with, say, 1/16th square Xs. That bowing means there's a tiny bit of "excess length- if the leg starts to bow out at attachment point, it will be able to pull the bowed X out a tiny bit, which may be enough for the leg bowing to "happen"- to go into column failure. Pre-tensioned strips allow essentially no motion.
You mentioned glueing Xs where they cross- you don't want to do that.

Really, why? I have always had success with gluing where the x's cross? How does this detriment the tower?

You do not want to use it in tension because when you glue the intersection you are basically making the strips smaller. The tension strength does not change when you change the length of the balsa strip, so gluing the joint just adds weight.

As for compression members, if simply depends on how much weight is being applied to it.

By the way, I recall this being discussed before.

[mrsteven]

Great! Any advice about this from other experienced grad's or builders too? (like mrsteven, slm, lkn, or balsaman?)

ha...ha... I love how I'm considered an experienced builder... I just started towers this year. All of my knowledge on this is from reading all the posts of the forums in towers/bridges for the last 6 or so years and stalking building events where I break down peoples designs and steal the portions of the designs I like. I've become very efficient at predicting loading capacity in this way. Helicopters/mission possible/robotics is really where I'm knowledgeable.

anyway.
Its better to NOT glue them because if your tower isn't totally evenly made and distributing of weight (which, by the way, is physically impossible. No such thing as 'perfection') then 1 of the bracings may be under tension more than another. With this, then your bending BOTH of them if glued with tension when the other one previously would of stayed essentially in place. This leads to premature failure. Also one of them may want to bow outwards and the other inwards if you design it like that so gluing them makes issues with their natural pattern of bowing.
This is my take on it.

[SLM]

I was wondering, what would be the effects of this:
Instead of placing the x's on the base on the same upper side of the main members (so that the cross members overlap and one bends over the other), what if you put one diagonal of the x on the upper side of the main members and the other diagonal of the x (going the opposite direction) on the bottom side of the main members so that there would be a gap the width of the main members in between the pieces, would this harm the construction in anyway, less stability or less strength (buckling, and contortion) because there would be no contact between the diagonals and no glue connecting them (like there would be if they overlapped). I figure this would be 1: easier to construct (less messy, less risk, neater), and 2: possibly more stable. However, I could be completely mistaken.

The most effective way of bracing a compression member is to glue the bracing not to the front or the back face of the member, but to the inside center of the member.

However, if I wanted to simplify the construction process by gluing bracings to the front (or back) face of the member, then I would have done it the same way you are suggesting; one diagonal glued to the front face and the other glued to the back face of the main compression member. The bracing is more effective this way because you are distributing its effect equally to both faces (front and back) of the member; you are not ignoring one face in favor of the other.

The gap between the two diagonals is not a problem. Think of it as having a bracing system for the front face of the compression member, and a separate bracing pattern for the back face of the member.

I would not glue the two diagonals even if they overlapped. Why? Because by gluing the two diagonals, you are unintentionally causing an additional force to develop in the diagonals that could cause unanticipated bracing failure. This is how:

Imagine two legs braced at the top and bottom using an X bracing (each diagonal connects the top of either leg to the bottom of the other leg). Under the applied load, the top of the legs are going to displace downward (since the load is pushing on them) and the bottom of the legs (resting on the table) are going to move outward on the table. This displacement pattern causes each diagonal of the X wanting to rotate a bit. One of the diagonals wants to rotate a few degrees in the clockwise direction while the other diagonal wants to turn, by a few degrees, in the counterclockwise direction. If you glue the two diagonals together at their mid-point, then you are restraining them from the rotation. Anytime you restrain the movement of a member (be it a bracing or a main member) you are causing additional forces to be developed in the member. The force created in this case is not a tension or a compression force, but a twisting force. If you have not designed the bracing to handle this twisting force, and if the force is large enough (that is, if the legs displacement is large enough), then one of the diagonals could break near the midpoint. This twisting force, however, is not going to develop if the diagonals are not glued together.

[pihi]

What's the best way to start this event? I just started this because apparently one of my team's tower member isn't able to go to regionals so I'm in need of some dire help right now. Anything would be helpful.

[thsom]

What's the best way to start this event? I just started this because apparently one of my team's tower member isn't able to go to regionals so I'm in need of some dire help right now. Anything would be helpful.

go to the wiki and copy the design in there, it does work, it may not hold everything but it works. The way it is scaled is that you place a diagonal every 5 cm on the chimney with a ladder and 3 x's on the base, 1 that takes up half, and the other 2 that take up 1/4th each. It works, it'll probably fail in the base though (maybe at 12 or so kg's unless you choose exceptional wood)

[pihi]

What's the best way to start this event? I just started this because apparently one of my team's tower member isn't able to go to regionals so I'm in need of some dire help right now. Anything would be helpful.

go to the wiki and copy the design in there, it does work, it may not hold everything but it works. The way it is scaled is that you place a diagonal every 5 cm on the chimney with a ladder and 3 x's on the base, 1 that takes up half, and the other 2 that take up 1/4th each. It works, it'll probably fail in the base though (maybe at 12 or so kg's unless you choose exceptional wood)

I've already looked and copied the wiki's build. It didn't last very long needless to say...I meant like other tips on how to make the tower stronger?

[sr243]

Yep, big tip here. Brace the bottom two legs by connecting the base of the legs to each other on the outside with a horizontal 3/32 by 1/16 membrane . This will help a lot in supporting the structure. It doesn't add too much weight and will stabilize the structure considerably, at least for me it did.

[pihi]

Yep, big tip here. Brace the bottom two legs by connecting the base of the legs to each other on the outside with a horizontal 3/32 by 1/16 membrane . This will help a lot in supporting the structure. It doesn't add too much weight and will stabilize the structure considerably, at least for me it did.

I'll try that in my next tower. I'm pretty much experimenting with different combinations at this point.

[thsom]

I'm surprised that the wiki design didn't work for you, with 1 or 2 alterations I got it to hold all 15 kg