Designs

[Balsa Man]

I am sure this has already been discussed, but I do not have time to wade through all of this thread...I apologize, but I have to ask:

-When attaching the legs of the base to the corresponding main shafts of the chimney, 1) do you use lap joints or butt joints? and 2) what angles should the two pieces of wood form, ideally?
-What are people doing as far as hieghts for the towers, with the new incentive for having a taller tower?

A couple things to think about back:
With all due respect, you .....come to the library (that's been created here); you don't have the time to read and learn, but you expect others to take their time to hand you what you want to know; there is a certain lack of respect in that......

Both the chimney and base legs have axial load running down through them; why would it make any sense to do anything but put the bottoms of the chimney legs right on top of the tops of the base legs? To offset and lap would put a twisting force in the structure, and take you from wood resting on wood, to wood depending on a glue joint in shear.

The angle?- "ideally" your base legs ought to be an the angle that will just clear the test base hole at the bottom and just fit in the 8cm circle at the top, and your chimney legs ought to go from just fitting the 8cm circle to fitting under the load block, with enough room to clear the 3cm eybolt eye.....

Again, I'm not trying to flame you; I'm saying take a little time to think.

[twototwenty]

@Balsaman
Thank you for your help...as far as me not having time, I at the moment am not doing towers and was simply interested in the answers to the questions I asked, but my time on scioly is usually spend reading about events I am doing. I thought my questions were reatively simple and easy to answer for someone experienced with towers...and once again, I appologize for not looking for them myself.

[Balsa Man]

@Balsaman
Thank you for your help...as far as me not having time, I at the moment am not doing towers and was simply interested in the answers to the questions I asked, but my time on scioly is usually spend reading about events I am doing. I thought my questions were reatively simple and easy to answer for someone experienced with towers...and once again, I appologize for not looking for them myself.

No prob, twototwenty.
I incorrectly assumed you were (doing towers), and weren't use the resource we've built together. So, my appologies; it was early, and I was grumpy.

I forgot to say something on height. When you run the numbers on this year's scoring system, and look at how many grams per centimeter the chimney would have to be under for height to be a positive factor (i.e., gain you points), even at Regionals, any.....reasonably light configuration is a plus, and that plus gets bigger at State, and even bigger at Nationals.

[thsom]

we get our wood from Specialized Balsa (in Loveland, Colorado); they have a website, do mail order, and sell weight-graded balsa sticks (and 1/64th sheet). They have bass, too, but not weight graded. Living close by, we're fortunate to be able to pick our sticks.

Do you know any other place that can deliver special density balsa wood? I'm wondering because I'm in Illinois and I'm not getting funded for this, the purchase of the wood alone will be $30 + 13 or so dollars for shipping which I just can't afford to buy time and time again.

[mrsteven]

we get our wood from Specialized Balsa (in Loveland, Colorado); they have a website, do mail order, and sell weight-graded balsa sticks (and 1/64th sheet). They have bass, too, but not weight graded. Living close by, we're fortunate to be able to pick our sticks.

Do you know any other place that can deliver special density balsa wood? I'm wondering because I'm in Illinois and I'm not getting funded for this, the purchase of the wood alone will be $30 + 13 or so dollars for shipping which I just can't afford to buy time and time again.

although you cant specify density, u can show up with a scale and weigh everything and figure out D yourself- the place I use is Venture Hobbies (in IL) I like in the North West burbs of Chicago- its up here in Buffalo Grove... idk where you are if thats even a feasible place to go.
if u do, call before to make sure they have the dimensions in stock. if they dont theyll order for you

[thsom]

Oh that's about 2 hours away. Thanks for your help though!

[LKN]

BalsaMan or SLM,

I understand that in the chimney, the horizontal bracing are under compression and the diagonal bracing is under tension. It makes sense.

Problem: My partner firmly believes he has a chimney design that has horizontal and diagonal bracing under tension. His "claim" is that when he constructs the chimney, each 2-D side, he builds it so the legs slightly bow outward in the center (not much at all, less than .5cm for sure if I had to guess). Apparently, he again slightly bows the 2 chimney sides (when going from "2-D" to 3-D) when he connects them together on paper. The concept he is trying to defend is that if the chimney legs are bowed outwards slightly in the middle, any force down on the chimney is going to want to cause the legs to bow outward, resulting in tension in all bracing, both horizontal and diagonal.

I am not quite sure how to explain that horizontal bracing is under compression and diagonal bracing is under tension, or how valid his argument is to begin with. I have tried the reasoning that when a tower is built, the slightly bowed out legs are going to want to restore to be straight legs, causing compression on the horizontal bracing, especially the horizontals in the center of the chimney. His theory is that it will hardly be under compression when building it, then go back to trying to say that as soon as force is put on the tower the chimney legs will want to bow outwards anyways resulting in all tensional forces.

What do you think? I can understand his perspective but don't think it holds true.

[mrsteven]

Just came back from an invite in IL and the top score was 106 (not efficiency, in the sci oly scoring system this year) weighing at 9.2 grams, holding full weight and 70.9 cm tall.

When talking to the supervisor, apparently at Belideir (sp?) competition, which was talked about earlier in here with thsom, the score was actually 135 and was achieved not by Stevenson, rather by another school that the name escapes my mind.

Stevenson is in the 100's ish range. Still better than what I've produced thus far but just an update from the IL towers competition and how scores are shaping up in sci oly in general

[thsom]

Oh not it was stevenson and the score was 120. and they did come in first so it wasn't possible for there to be a 135. I actually watched them load their tower and heard the mass, height, and weight held at near 120. was this score of 135 at your invite or *belvidere* because if you are saying it was from belvidere, I'm afraid you may be mistaken

[mrsteven]

Oh not it was stevenson and the score was 120. and they did come in first so it wasn't possible for there to be a 135. I actually watched them load their tower and heard the mass, height, and weight held at near 120. was this score of 135 at your invite or *belvidere* because if you are saying it was from belvidere, I'm afraid you may be mistaken

just letting you know what the event supervisor told me- nothing more nothing less

Heres an interesting question: At todays invite, I saw a tower with the base Xs being overlapped with eachother creating a 'waffle weave' type design. It struck me as odd, as I don't see those often. The structure didnt hold the mass (around 13 I believe it held) but the base wasnt the point of failure. Although the tower itself wasn't built competitively, I wonder about the concepts ability to yield results as their wood working skills increase. Any comments or reasons why this would be ineffective versus the traditional X pattern where the X's don't over lap?