Balsa Man wrote:mrsteven,
Uh, per my earlier msg laying out densities and dimensions, we're not using any 1/16thx1/16th. For Xs, as I said, we're using 1/16th wide strips cut from 1/64th sheet (sheet weight at 3"x36 inches from 7.5 grams up (to around 9grams). This is pretty high density stuff. The 0.2, .3, .4 at 1/16th x 24" you got is pretty low density, which means it's tensile strength is pretty low. I would not expect it to work for Xs seeing tension loading....
either a balsa cutter (not terribly expensive) or really carefully with an exacto knife. However, I wouldnt recommend the exacto unless you have a really solid metal straight edge (you KNOW is totally straight) and a bit of materials skill
If neither... buy strips... more expensive but I prefer, given I get the right density
2011 Helicopters State Runner-up
2012 Helicopters State Champion
2013 Robot Arm State Champion
minniemouse wrote:Bracing one inside and one outside is good for X bracings? I haven't heard of this before. Also, when using the X bracings, do you overlap the two pieces in the middle?
We have had no issues with inside/outside bracing for the X pattern. The two pieces do not need to physically touch each other. If the gap in between them is small (in our case it is less than 1 mm), it would not adversely affect the tower. Further, even if the diagonals overlap, assuming the tower was designed and built properly, there is no need to glue them together.
Responding to multiple things...
We cut with a single edge razor blade and a good steel straightedge.
Not glued where they cross- they are touching.
I was not aware you could buy 1/64thx1/16th strips, mrsteven; were?
Balsa Man wrote:Responding to multiple things...
We cut with a single edge razor blade and a good steel straightedge.
Not glued where they cross- they are touching.
I was not aware you could buy 1/64thx1/16th strips, mrsteven; were?
Oh those dimensions, you are correct one must make them yourself.
Its available to purchase up to 1/32 small I believe (dont quote me on that, the smallest i use for anything is 1/16 but i think I saw 1/32 floating around somewhere...)
2011 Helicopters State Runner-up
2012 Helicopters State Champion
2013 Robot Arm State Champion
I mentioned beforehand that my tower chimney is about 7 grams, which is the heaviest part of my tower. I felt that the chimney was where I could start taking off wood.
So far it is a really basic design (simplicity is usually the best solution) and involves a bracing design that looks like:
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12 of each bracing for the 55cm chimney. The legs are 1/8 by 1/8 balsa and the bracing is 1/16 by 1/16. Are there any tips for significantly reducing the weight of the chimney? (ex. down to 3 or 4 grams?)
flyingwatermelon wrote:I mentioned beforehand that my tower chimney is about 7 grams, which is the heaviest part of my tower. I felt that the chimney was where I could start taking off wood.
So far it is a really basic design (simplicity is usually the best solution) and involves a bracing design that looks like:
\
/
\
/
12 of each bracing for the 55cm chimney. The legs are 1/8 by 1/8 balsa and the bracing is 1/16 by 1/16. Are there any tips for significantly reducing the weight of the chimney? (ex. down to 3 or 4 grams?)
Well I'm a noob so don't trust me, trust SLM or Balsa Man but
I think that 1/8x1/8 is too much. I'd suggest 3/32 for legs and 1/16 for bracings
A tip to cut the weight in half?- sure, use 1/16th x 1/16th unobtanium.
Seriously, you're way over-reaching; going from a... respectable... weight to a weight that would win nationals.
There are no migic answers for a leap like that. Is it holding full load at 11gr?
1/8th is not necessarily "too much", it depends on the density, and it depends on the bracing interval, and it depends on the effectiveness of your bracing in creating sufficiently short exposed column lengths. There is no "best" size- its how you work size, density, and bracing interval to get a combination that weighs less that is the path to improving performance.
Someone from New Jersey just posted a picture of a tower in the Gallery, asking for thoughts on the X-bracing used on a test tower built to explore X-bracing . For some reason, I could not get a comment to go in there.....
So,
What X-bracing (or Z-bracing; any bracing configuration) is all about is just that; bracing; bracing a leg at points along it to shorten the exposed column length. Shorter column sections carry more load than longer ones (Euler's Buckling Theorem), as discussed at length in previous posts by a number of folk here. By putting in some "bracing sets", be they ladders and Xs-two diagonals, ladders and a single diagonal-Z-bracing, you create in the legs a set of "stacked columns"- shorter column sections of the long, overall leg column; the bracing "anchors" the points where it intersects the legs in space; bracing it against the movement that happens as it begins to buckle. Each "brace set" - looking at just one side of the tower, is stabilizing a trapezoid, which is defined by the 4 points where the bracing attaches to the leg. Depending on which way a leg is trying to start to buckle, bracing pieces see tension of compression loading. In an Xs and ladders system, the Xs see tension, the ladders compression. In an "open X" approach, as shown in this picture, the Xs see/would have to handle both.
So, looking at the picture
First, the X-s in the base are doing nothing, in terms of bracing the lower legs against column/buckling failure; the exposed column length is the full length of the leg. They do stabilize the ends, acting to prevent deformation of the trapezoid defined by tops and bottoms. If there were two X-sets in the bottom, effective column length would be cut in half; buckling strength would go up by a factor of 4.
Second, going up to the chimney, the lack of ladders means both sides of each X must handle both compression and tension (depending on which way buckling distortion tries to come in). At the relatively long lengths, and small cross section (looks like 1/16th), they will be pretty ineffective in compression (long length = low buckling strength, unless they are in pretty high density (that is heavy) wood. Remember, X-braces loaded in compression act the same as a leg- failure will be as buckling column failure. In the tension loading direction(s), at any reasonable density, pretty light, say 0.4, 0.5 gr/36" stick, they'll work. To handle much compression loading...?0.9, 1.0 gr/36, and even then, I'd guess to well short of full load.. Now with low density ladders added handling the compression bracing, and fairly low density Xs, then it would be braced.
That it is weak and wobbly is exactly what you would expect.
