Towers B/C

[kinghong1970]

Is there any regulation for the size of the S hook and the chain? What would be a good estimate for the chain and s hook to be? Thanks.

Nope
And this is why going for the super light tower for just the bonus and tier 1 is so dangerous...

I’ve seen some thick and heavy chain and hooks at the tournaments

[Balsa Man]

Hi,

I convinced my son and his partner to build tower with 2 part jig first so that they will appreciate the one-jig approach more later.

They took 2 hours to build the chimney, 2 hours to build the base and 3 hours to put them together.

This is a snapshot I took before they trim off the top close to the top ladder.


The 1/8 stick picking thresholds are from Balsa Man’s spreadsheet. Base with 5 intervals and chimney with 7 intervals. The base they used 1/8 stick with BS around 40g (@36 inch) while the threshold is 21g.

The tower held 7.13 kg in Golden Gate invitation (12th place). While I was there, I saw similar towers also hold around 8kg (one is from Hawaii). They all crashed at the base. By similar, I mean all X with 5 intervals for base.

From video, my son told me that the second X from bottom bent inside gradually and then snapped. When they built, I knew they oriented the legs to bend outward.

The materials are from limited left overs.
============
Chimney leg: all 17 inch cut from BS 36 at 36 inch (threshold 29 from spreadsheet)

# weight(g) BS(g) calculated BS(g) at 36 inch
1 .58 117 26
2 .59 160 35
3 .56 130 29
4 .64 180 40
5 .61 163 36
6 .55 133 30
7 .58 160 35
8 .60 180 40

I believe they pick #2, #4, #5, and #7.

Chimney brace: strip 1/16 X 1/32 from 1/32X3X36 sheet with 6 grams
==========
Base leg: all 9.875 inch cut from 36 inch with BS=39 (threshold 21 from spreadsheet)
# weight(g) BS(g) calculated BS(g) at 36 inch
1 .37 460 34
2 .39 540 40
3 .44 660 49
4 .40 520 39
5 .40 630 47
6 .40 540 40
7 .45 640 48
8 .42 555 42

They picked #2, #4, #6, and #8.

Base brace: strip from 1/32 X 3 X 36 with 10 grams. Their other sheets are so heavy > 16g, I convince them to cut wider from the 10 gram sheet for the lower X.
2 lower X: 3/32 X 1/32 strip
3 upper X: 1/16 X 1/32 strip
===========
I recommend them to scale the calculation from their own data and try another all X base with 7 intervals. Also try a ladder plus X with 4 intervals.

============
Many thank for Balsa Man for the spreadsheet and the formula. Also thanks for the guy recommended for the glue applier built with 0.2mm music wire and a stick. I cannot find the article anymore. Now they use way less glue and no more sticky fingers.

Jinhu

Thanks for the nice clear picture and wood details.
That's a good looking construction job!
What jumps out at me is the lack of a tension strip around the bottom of the base. As discussed in a few posts, the leg ends are pushing out away from each other w/ a force of a bit over 2kg, so you absolutely want a strip around the bottom tro keep the leg ends from pushing out. Parallel to the test base surface, Up about 1/16" (so it doesn't touch the base surface. We run 1/16" strips cut from 1/64th" sheet (fairly hi density sheet- 8-9gr for 3x36" sheet). I believe that just with that addition, that tower would have held a lot more; 10, 12, 14kg???

[Balsa Man]

Is there any regulation for the size of the S hook and the chain? What would be a good estimate for the chain and s hook to be? Thanks.

Nope
And this is why going for the super light tower for just the bonus and tier 1 is so dangerous...

I’ve seen some thick and heavy chain and hooks at the tournaments

I agree completely.
See next thread below

[dholdgreve]

Is there any regulation for the size of the S hook and the chain? What would be a good estimate for the chain and s hook to be? Thanks.

Since we also have teams competing, it would not be fair if they knew the weight of the chain and block without sharing this to all the other competing teams, which is why we always send this info out ahead of time, so that no one team has an unfair advantage.

[jinhusong]

Thanks for the nice clear picture and wood details.
That's a good looking construction job!
What jumps out at me is the lack of a tension strip around the bottom of the base. As discussed in a few posts, the leg ends are pushing out away from each other w/ a force of a bit over 2kg, so you absolutely want a strip around the bottom tro keep the leg ends from pushing out. Parallel to the test base surface, Up about 1/16" (so it doesn't touch the base surface. We run 1/16" strips cut from 1/64th" sheet (fairly hi density sheet- 8-9gr for 3x36" sheet). I believe that just with that addition, that tower would have held a lot more; 10, 12, 14kg???

Hi Balsa Man,

Thanks. I will tell them to try that first.

Jinhu

[Balsa Man]

Thanks for the nice clear picture and wood details.
That's a good looking construction job!
What jumps out at me is the lack of a tension strip around the bottom of the base. As discussed in a few posts, the leg ends are pushing out away from each other w/ a force of a bit over 2kg, so you absolutely want a strip around the bottom tro keep the leg ends from pushing out. Parallel to the test base surface, Up about 1/16" (so it doesn't touch the base surface. We run 1/16" strips cut from 1/64th" sheet (fairly hi density sheet- 8-9gr for 3x36" sheet). I believe that just with that addition, that tower would have held a lot more; 10, 12, 14kg???

Hi Balsa Man,

Thanks. I will tell them to try that first.

Jinhu

You're quite welcome. One thing I forgot to mention - when putting these strips on, make sure they have no slack in them - cut them longer than needed, glue one end on, then grab the end sticking out, put glue on the leg where it goes, and pull the strip nice and taut and move it onto the glue/leg.

[dholdgreve]

By pulling these X braces tight, does it ever cause the columns to bow inward? I'd think that repeatedly snugging these braces may cause a compounded effect on the columns, no?

[Balsa Man]

By pulling these X braces tight, does it ever cause the columns to bow inward? I'd think that repeatedly snugging these braces may cause a compounded effect on the columns, no?

Ah, good question. Pulling too tight could cause problems on X braces (for an all Xs bracing setup)- I was referring to the tension strips at the bottom of the tower. It is especially important to have no slack at all in the tension strips. With a jig that is holding the lower part of the base legs in position, and a reasonable level of pulling....1/2, 3/4 of a pound or so, legs don't get displaced.

In the Xs, you want them straight, no slack, but not 'pulled' - especially at points on the jig where they're not snugly held in place.

[pjspol]

I am not sure if this has been discussed at length this year, but I was wondering about the benefits / downfalls of utilizing a rectangular, bridge-like base rather than the typically square base. This seems especially pertinent because of the wide angle on bonus towers. I have seen some high level teams utilize this bridge-like base design, but from what I found, it is much easier to achieve a very competitive weight with the traditional square base.

The traditional square base with bonus for this year requires approximately 4 23cm and 4 40cm segments of main compression member size. The bridge-like design (at least the one I saw) would require 4 60cm segments from top to bottom in the main column, 2 30cm segments as the base of the bridge, and 4 ~23cm segments as supports from the bridge ends to the main column, all of which need to be of fairly large dimension (main compression member size).

Any ideas?

[Raleway]

I am not sure if this has been discussed at length this year, but I was wondering about the benefits / downfalls of utilizing a rectangular, bridge-like base rather than the typically square base. This seems especially pertinent because of the wide angle on bonus towers. I have seen some high level teams utilize this bridge-like base design, but from what I found, it is much easier to achieve a very competitive weight with the traditional square base.

The traditional square base with bonus for this year requires approximately 4 23cm and 4 40cm segments of main compression member size. The bridge-like design (at least the one I saw) would require 4 60cm segments from top to bottom in the main column, 2 30cm segments as the base of the bridge, and 4 ~23cm segments as supports from the bridge ends to the main column, all of which need to be of fairly large dimension (main compression member size).

Any ideas?

I personally dislike the "bridge approach." Although it seems at first it would be easier to put together and what not, other factors come into play. As described, it is "bridge" like. Actually, the base is quite literally a bridge; that means it also has to take into account torsion and all those other more nuanced forces. Being so tall but also so thin, toppling is far more of an issue. The connection should be easier but then building such an unwieldy structure requires more attention elsewhere. Both have their merits but to get above 3,000 I believe the traditional square base is far better. Now here's Balsaman, with the much better analysis.