|
deltaops88
|
Re: TOWER HELP [TBC] |
Posted: 04-08-06 00:41:48 |
|
Junior Member
Location:
Joined: 15th Jun 05
IP: Hidden
|
i would definitely hesitate before saying any one style of bracing is better than another. every configuration has its purpose. but thats just my opinion....
|
Last edited by: deltaops88 on 04-08-06 00:42:50
|
|
|
|
|
|
|
|
|
|
fantasymage89
|
Re: TOWER HELP [TBC] |
Posted: 04-11-06 13:12:52 |
|
Junior Member
Location: Mason, Ohio
Joined: 21st Mar 05
IP: Hidden
|
Well first off, less weight isn't always better. If your tower weighs only 3 grams for instance, but only holds a kilogram, you won't place.
Anyways though, gotta question. X-bracings have been the popular thing here apparently, but what about V's. A V, then inverted V, so it pretty much makes an X in the overall picture. Does that make a difference (pos or neg?)? It would take less wood I think, since the V's are slightly shorter than X's. It's also a bit easier IMO, but again, is it worth it, or does it not matter?
thankee mucho
|
|
|
|
|
|
|
|
|
mick4state
|
Re: TOWER HELP [TBC] |
Posted: 04-12-06 07:55:22 |
|
Member
Location: West Ottawa (WOSO)
Joined: 5th Dec 05
IP: Hidden
|
The V and then the ^ shapes will still make and X, so you are just adding weight in the form of glue at the cencer of this newly formed X.
Tiny towers can be bad, but excess weight is what Westilium is talking about. If your main legs break, your crossmembers obviously had extra strength they didn't need, so they can be lightened so save a few efficiency points.
-mick
|
--------------------
i talk to much...
'05 - Chem ID, Chem Lab, Fermi Questions, PDG
'06 - Fermi Questions, Forencics, Physics Lab, PPS, Scrambler, Tower
|
|
|
|
|
|
|
|
highschooler
|
Re: TOWER HELP [TBC] |
Posted: 04-12-06 08:53:06 |
|
Senior Member
Location: OHIO
Joined: 14th Aug 03
IP: Hidden
|
Quote: Originally posted by Westilium
The best bracing is the one that uses the least amount of wood.
Less wood = less weight = kicking butt |
|
|
wrong as one can possibly be.
dont build according to his method. u wont win.
support: i had an average ranking of 1.16 in tower building. my only loss was to West Ottawa in clio inviational.
|
|
|
|
|
|
|
|
|
mick4state
|
Re: TOWER HELP [TBC] |
Posted: 04-13-06 09:53:30 |
|
Member
Location: West Ottawa (WOSO)
Joined: 5th Dec 05
IP: Hidden
|
And this is the builder from West Ottawa that beat him.
You are taking what she is saying out of context. An overall lighter tower is not necessarily more efficient, but that is not what she is suggesting. The point is to cut down on any weight that is superfluous. If the crossmembers are not the part of your tower that is breaking, then you can lighten them without hurting the maximum efficiency of the tower. Ideally, to save the most weight, every single point in your tower should break all at once.
The builder from Solon is right in that lighter towers aren't as structurally sound as heavier ones. Your tower should be light enough so that it breaks, but not much before the whole 15kg has been supported.
Point - If the bracing isn't the part that's breaking, then that is a place where you can cut down on mass, and therefore increase efficiency. Less bracing is good, to a point. And that point is where the bracing and the rest of the tower all break at the same time.
-mick
PS - Whether or not a tower wins awards at an invite or regionals (or maybe even state) doesn't depend so much on very tedious things like how you make your bracing, but more on how well the tower is built. Even with wildly inefficient designs, we've managed to make towers that would have taken a medal at regionals. Spend more time on building well and with good technique than with things like Z vs X bracing. Practice is the best thing. Make practice towers... lots of them.
Personal Preference - X bracing withOUT gluing the centers.
|
--------------------
i talk to much...
'05 - Chem ID, Chem Lab, Fermi Questions, PDG
'06 - Fermi Questions, Forencics, Physics Lab, PPS, Scrambler, Tower
|
|
|
|
|
|
|
|
|
|
|
mick4state
|
Re: TOWER HELP [TBC] |
Posted: 04-13-06 22:13:00 |
|
Member
Location: West Ottawa (WOSO)
Joined: 5th Dec 05
IP: Hidden
|
I agree.
As for efficiencies - I've tried to get some out of people, but they just won't talk, but I'll play.
Our best towers were our towers from regionals and the weeks before, which topped out around 2800. We could do better for State, since our tower at the previous competition held it all and therefore had excess weight, so look for a strong showing there.
Mostly, I'm just hoping for competition. I have only lost to our own JV team on a randomly good tower they build. The closest teams to me have been Solon at Clio and GH at regionals. GH was a good 500 points behind our tower and at Clio our avg efficiencies were much lower, but we still won by a bit. I dunno...
I heard rumors of a tower that got 3031 on the east side of the state, but that could easily be hear-say.
-mick
|
--------------------
i talk to much...
'05 - Chem ID, Chem Lab, Fermi Questions, PDG
'06 - Fermi Questions, Forencics, Physics Lab, PPS, Scrambler, Tower
|
|
|
|
|
|
|
|
|
|
|
newbie33
|
Re: TOWER HELP [TBC] |
Posted: 04-14-06 08:18:27 |
|
Junior Member
Location:
Joined: 2nd May 04
IP: Hidden
|
Quote: Originally posted by Valpo Towers and Trebs
Quote:| Personal Preference - X bracing withOUT gluing the centers. |
|
|
thats not just a personal prefence it is the obvious way to go. There is no force on that point so it is just adding useless mass. A lot of people don't realize how much the glue actually weighs. Other team members and I have made the exact same tower design but theirs would be almost 2-3 grams heavier. Mine would hold more too mostly because they are pretty poor tower builders.
Also bracing rarely BREAKS but it does bend alot if it is not strong enough. This bending will signifigantly weaken the main beams and cause the tower to break. I have never had a brace BREAK but maybe others have because of construction flaws.
Lighter towers are almost always better if you know the right way to build them. The lighter your tower the better your design must be and the better the quality of the build must be. If you have more experience it is better to build a much lighter tower because obviously you can get a better score and you can do it right. If you are a noob then it is better to build a hevier tower because it allowes for more room for error and it is much safer(less likely to break at low mass)
BTW What are all your best efficiencies mine is about 2500
|
|
|
that is the most useless entry i have ever read. what a whole bunch of crap. don't tell us common sense....
why don't u care to explain WHY not gluding the X would be better? maybe scientifically instead of some crap thats not backed up by anything?
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
mick4state
|
Re: TOWER HELP [TBC] |
Posted: 04-14-06 21:09:59 |
|
Member
Location: West Ottawa (WOSO)
Joined: 5th Dec 05
IP: Hidden
|
Simmer down guys.
The gluing adds weight. Weight lowers efficiencies. The added weight does not make good for itself in strength enough to matter. My logic is as follows...
Members in tension do not need the glue to hold them in place, and it could actually cause the wood to break prematurely since it has now two short sections instead of one long one.
In compression, the gluing could prevent the bracing from bulging out, but the fact that it's divided by a anchor point in the center means it will actually likely snap sooner. Try snapping a piece of balsa. See how far it bends and how much force you have to put on it. Then try with half that length. The smaller halved crossmember requires a smaller compression than the full crossmember to reach it's breaking point.
That's the science behind it that I can think of off the top of my head. If it weren't a friday night, I would look more into it.
-mick
|
Last edited by: mick4state on 04-14-06 21:10:46
--------------------
i talk to much...
'05 - Chem ID, Chem Lab, Fermi Questions, PDG
'06 - Fermi Questions, Forencics, Physics Lab, PPS, Scrambler, Tower
|
|
|
|
|
|
|
|
nam_g
|
Re: TOWER HELP [TBC] |
Posted: 04-14-06 21:59:38 |
|
SciOly OldHat
Location:
Joined: 3rd Jan 03
IP: Hidden
|
Quote:| Try snapping a piece of balsa. See how far it bends and how much force you have to put on it. Then try with half that length. The smaller halved crossmember requires a smaller compression than the full crossmember to reach it's breaking point. |
|
|
That isn't true. The shorter a piece is, the more pressure it can support in compression. You will find by doing that test that the shorter piece holds more than the longer piece.
This:
--> ----------------- <--
Holds less than this:
--> ------- <--
Where the --> and <-- are showing how the force is applied.
|
|
|
|
|
|
|
|
|
|
|
|
rjm
|
Re: TOWER HELP [TBC] |
Posted: 04-14-06 23:19:03 |
|
Member
Location: Grand Haven, MI
Joined: 31st Mar 02
IP: Hidden
|
Nam-g is right on this one. Gluing the braces in the center cuts the effective length of the compression brace in half. The science of it is most simply summarized in Euler's buckling formula, S=(pi)^2*E/((Le/r)^2), where S is the critical buckling stress from the axial compressive load on the brace, E is the modulus of elasticity (or Young's modulus) of the wood, Le is the effective, or unbraced, length of the compressive member, and r is the radius of gyration of the cross section of the compressive member. A short column will fail at the crushing strength of the wood, but a slender column (or brace) will fail at a much lower load by buckling. Restraining a column or brace at its center gets you closer to the crushing strength.
A buckling analysis is more useful in estimating the spacing of the bracing on the legs of the truss than in estimating the compressive capacity of the bracing itself. It is basically impossible to accurately estimate the compressive load on bracing struts. On the other hand, it is a simple matter to estimate the load in each leg, if you know that the load is evenly distributed and you know the angle of the leg from vertical.
It is an oversimplification to say that bracing is either in tension or unloaded. The wood in the bracing is elastic, and as the bracing resists the buckling of the legs, the tension brace stretches a bit and allows the braced panel of the tower side to deform. That puts at least some compressive load on the "unloaded" side of the "X". Also, the buckling situation is unstable and the stresses can easily reverse during the loading, so that the braces may stretch and compress alternately. In short, the compression side of the "X" brace really is doing some work. If you carefully watch during loading, you can usually see the strain in the braces.
I can easily see how gluing the braces in the center will cut the effective length of a compressed brace in half and more than double it's strength. Restraining the compressive strut in its center does not cause it to snap sooner; bulging is bad. I can't see how the tensile strut is harmed - tensile struts are forced to straighten under the tensile load, and a sideways load would have to be substantial to break it or have much effect. It's a bit like breaking a rope by pushing sideways on its center. It certainly does not convert the tensile strut into two short struts. I think the compressive strut will break before it can take out the tensile strut.
Whether or not gluing the centers of the Xs is worth the extra weight is an open question. We glue ours, it adds very little weight - less than .1 grams -after all, you don't need a glob of glue, just a film. (This extra weight would not have changed our ranking in our regional tournament, unless actually it prevented a failure.) I think it is more valuable on the long braces near the bottom, and not valuable in the short bracing at the top. I wouldn't preach to anyone about it, or dispute the success you've had with either gluing or not gluing braces. Results will vary with the bracing design, size, and quality of the wood. Base your decisions on sound structural analysis.
Bob Monetza
Grand Haven, MI
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
-Alaska