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I recently tried doing a tower with the P1 type bracing from the Wikipedia. It cut about 1 gram from our tower and it held about the same, also arranged it so there aren't any empty spots. Has anyone else tried this type?

The problem I find with that bracing is that there is little strength compression wise. You would have to have very strong bracing which I wouldn't think would be worth it for only 1 gram.

cheese wrote:The problem I find with that bracing is that there is little strength compression wise. You would have to have very strong bracing which I wouldn't think would be worth it for only 1 gram.

To make sure that there isn't as much of a chance for compression, we have the top of our chimney be 4.5cm wide and the base is 5.5cm. Correct me if I'm wrong though

M017 wrote:

cheese wrote:The problem I find with that bracing is that there is little strength compression wise. You would have to have very strong bracing which I wouldn't think would be worth it for only 1 gram.

To make sure that there isn't as much of a chance for compression, we have the top of our chimney be 4.5cm wide and the base is 5.5cm. Correct me if I'm wrong though

The main reason that the top should be skinnier is for stabilization. This drawing https://docs.google.com/drawings/d/1q8x ... sp=sharing
depicts how with a greater leg angle (the 4.5 going down to 5.5) will increase force towards the middle (compression).

cheese wrote:

M017 wrote:

cheese wrote:The problem I find with that bracing is that there is little strength compression wise. You would have to have very strong bracing which I wouldn't think would be worth it for only 1 gram.

To make sure that there isn't as much of a chance for compression, we have the top of our chimney be 4.5cm wide and the base is 5.5cm. Correct me if I'm wrong though

The main reason that the top should be skinnier is for stabilization. This drawing https://docs.google.com/drawings/d/1q8x ... sp=sharing
depicts how with a greater leg angle (the 4.5 going down to 5.5) will increase force towards the middle (compression).

Ok, that makes sense now. So would 4.5 to 4.5 just depend on which way the balsa decides to go?

Not necessarily "decides", but any part that isn't level, even by half a millimeter, would be wear the tower would tip over with 4.5 to 4.5.

cheese wrote:Not necessarily "decides", but any part that isn't level, even by half a millimeter, would be wear the tower would tip over with 4.5 to 4.5.

Wait, but wouldn't the top work the same as a miniature version of last years tower? Our tower only used tension pieces and scored 1800 last year and it held the whole 15kg

What's the best bracing type to use?

cheese wrote:Not necessarily "decides", but any part that isn't level, even by half a millimeter, would be wear the tower would tip over with 4.5 to 4.5.

Before gluing the top and bottom halves together, I use the level thingy behind the compass on my iPhone to make sure its flat, and sand it down if it's not.

FWIW, I agree that having the top smaller than the bottom of the upper section is a good idea... but not for the same reasons cited... You can't state categorically that the legs will bow inward just because the top is smaller than the bottom of the chimney... It depends on what is happening between those 2 points. If the columns have a slight (1 mm) bow outward, that is all it takes to set the predisposed direction of the buckling. They will now bow outward, putting the bracing and ladders in tension, a very slight inward bow will predispose to compression. If you do a perfectly vertical SFPD, you will find that most columns will have a "preference" as to which way they intend on bowing under load. Mark this edge and factor this into your build. Also keep in mind that every time you add a ladder, you effectively separate the column into individual stacked columns. This can result with a sort of harmonic wave sort of pattern. Lets say you have 7 tiers of bracing, the middle tier (tier 4) may be predisposed to bow outward, forcing the tiers above and below (3 & 5) to bow inward, thus forcing tiers 1 and 7 to also bow outward. Each Ladder will in effect, function as a fulcrum,