Towers B/C

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Re: Towers B/C

Post by Unome » October 29th, 2016, 4:59 pm

baker wrote:Event Super Question - A tower built so it spans the 29 cm circle. Team places the loading block, chain and bucket on the tower, but before they are able to load any sand the tower collapses. Do they get the 2 kg bonus as their score?
For example an 2000 gm load (bonus) / 8 gram tower = 25 score
Is the team usually scored if they hold only the loading block, chain and bucket? Usually I've heard that if they can hold the apparatus it's scored with the apparatus' weight, but if it collapses immediately after loading it's scored in tier 4.
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Re: Towers B/C

Post by baker » October 29th, 2016, 5:21 pm

Unome wrote:
baker wrote:Event Super Question - A tower built so it spans the 29 cm circle. Team places the loading block, chain and bucket on the tower, but before they are able to load any sand the tower collapses. Do they get the 2 kg bonus as their score?
For example an 2000 gm load (bonus) / 8 gram tower = 25 score
Is the team usually scored if they hold only the loading block, chain and bucket? Usually I've heard that if they can hold the apparatus it's scored with the apparatus' weight, but if it collapses immediately after loading it's scored in tier 4.
Not sure of the tier 4. Since the total mass is the bucket, chain, loading block and then the sand... it seems loading begins when the bucket, chain, block is placed. If it holds for awhile as the students get ready to add the sand isn't it already in play? If it breaks down while hooking up the bucket, chain, block...well you can't load so that would be tier 4

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Re: Towers B/C

Post by Balsa Man » October 29th, 2016, 6:38 pm

baker wrote:
Unome wrote:
baker wrote:Event Super Question - A tower built so it spans the 29 cm circle. Team places the loading block, chain and bucket on the tower, but before they are able to load any sand the tower collapses. Do they get the 2 kg bonus as their score?
For example an 2000 gm load (bonus) / 8 gram tower = 25 score
Is the team usually scored if they hold only the loading block, chain and bucket? Usually I've heard that if they can hold the apparatus it's scored with the apparatus' weight, but if it collapses immediately after loading it's scored in tier 4.
Not sure of the tier 4. Since the total mass is the bucket, chain, loading block and then the sand... it seems loading begins when the bucket, chain, block is placed. If it holds for awhile as the students get ready to add the sand isn't it already in play? If it breaks down while hooking up the bucket, chain, block...well you can't load so that would be tier 4
Looks to me like the rule is clear (6 a.); minimum load that can be be scored is weight of "loading block assembly" (bucket, chain, block, eyebolt.nut/washer). If the tower carries that (and there is no 'has to hold for x seconds' language, but would have to be for....some perceptible time), it is scored. Depending on chain....thats 500-1000gr, call it 800, so load scored would be 2800. Its not going to take an 8 gram tower to carry the 'load block assembly- more like...3 or 4gr; at 4gr, 2800/4 = 700.
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Re: Towers B/C

Post by Kenshi Takahashi » October 29th, 2016, 8:17 pm

baker wrote:
Kenshi Takahashi wrote:When the rules say the tower must span a 20x20 cm hole, does it mean that the tower's base must have minimum dimensions of 20x20 cm, or that it simply needs to cross the 20x20 gap?
You can rotate a 4 legged tower so you hit the center line (10 cm) of each 20 cm side. A tower base around 15 or 16 cm square should work.
Oh ok. So is a rectangular base OK as long as it spans the 20 cm gap?
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Re: Towers B/C

Post by dholdgreve » October 31st, 2016, 6:10 am

Balsa Man wrote:
baker wrote:
Unome wrote: Is the team usually scored if they hold only the loading block, chain and bucket? Usually I've heard that if they can hold the apparatus it's scored with the apparatus' weight, but if it collapses immediately after loading it's scored in tier 4.
Not sure of the tier 4. Since the total mass is the bucket, chain, loading block and then the sand... it seems loading begins when the bucket, chain, block is placed. If it holds for awhile as the students get ready to add the sand isn't it already in play? If it breaks down while hooking up the bucket, chain, block...well you can't load so that would be tier 4
Looks to me like the rule is clear (6 a.); minimum load that can be be scored is weight of "loading block assembly" (bucket, chain, block, eyebolt.nut/washer). If the tower carries that (and there is no 'has to hold for x seconds' language, but would have to be for....some perceptible time), it is scored. Depending on chain....thats 500-1000gr, call it 800, so load scored would be 2800. Its not going to take an 8 gram tower to carry the 'load block assembly- more like...3 or 4gr; at 4gr, 2800/4 = 700.
Len,
I've run this event quite a bit at various invitationals. Based on the way the kids set it up, I could see giving the credit for the chain, eyebolt, and loading block. Then, if they hang the bucket and it holds for some perception of time, I could give credit for that as well. If it breaks while their hand is still on the bucket (process of hanging it) they would receive credit for the block, chain, and eyebolt only (plus the bonus, if outside the 29 cm ring). I really hate tiering anyone to tier 4.
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Re: Towers B/C

Post by hearthstone224 » October 31st, 2016, 8:18 am

Hey sorry for changing the subject, but

1. can I say that the leg itself will have to have

4608/8.91 = 517.17 or greater for the BS of a leg 36'' long?

Then

4608/20.11 = 229.1 or greater?

Then so on until 1/8th interval (which is where I stopped?)

I called this the "safe strength", where if it holds more or equal to this amount, it should theoretically hold the load we want?

I get 4608 because that is the safe threshold for 20% variation, and then the multiplier is what I calculated earlier.

2. This question is pretty weird- But we can't use the glue we use for gluing balsa together, right? We need to buy special glue for gluing plastics together? If so could someone possibly post a link of an example for me to buy? This is for the jig construction.

3. Can someone find me a link for 1/4 plexiglass I need to use for the base?
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Re: Towers B/C

Post by jander14indoor » October 31st, 2016, 11:20 am

Not knowing what glue you use for balsa, I'll just say CA (superglue) holds some plastics just fine. Others not so much. And for some plastics you need the odorless stuff or you may cause cracking/dissolving. Try it and see.

If you are using Testor's balsa cement, Ambroid, or similar, those won't work with most plastics.

You need an appropriate solvent glue for some plastics.

Gorilla Glue (the stuff that foams) will hold a wide range of plastics, some that CA won't, but not all..

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Re: Towers B/C

Post by Balsa Man » October 31st, 2016, 3:45 pm

dholdgreve wrote:
Balsa Man wrote:
baker wrote:
Not sure of the tier 4. Since the total mass is the bucket, chain, loading block and then the sand... it seems loading begins when the bucket, chain, block is placed. If it holds for awhile as the students get ready to add the sand isn't it already in play? If it breaks down while hooking up the bucket, chain, block...well you can't load so that would be tier 4
Looks to me like the rule is clear (6 a.); minimum load that can be be scored is weight of "loading block assembly" (bucket, chain, block, eyebolt.nut/washer). If the tower carries that (and there is no 'has to hold for x seconds' language, but would have to be for....some perceptible time), it is scored. Depending on chain....thats 500-1000gr, call it 800, so load scored would be 2800. Its not going to take an 8 gram tower to carry the 'load block assembly- more like...3 or 4gr; at 4gr, 2800/4 = 700.
Len,
I've run this event quite a bit at various invitationals. Based on the way the kids set it up, I could see giving the credit for the chain, eyebolt, and loading block. Then, if they hang the bucket and it holds for some perception of time, I could give credit for that as well. If it breaks while their hand is still on the bucket (process of hanging it) they would receive credit for the block, chain, and eyebolt only (plus the bonus, if outside the 29 cm ring). I really hate tiering anyone to tier 4.
Dan, that makes sense to me; I've done that a couple times in that situation
jander14indoor wrote:Not knowing what glue you use for balsa, I'll just say CA (superglue) holds some plastics just fine. Others not so much. And for some plastics you need the odorless stuff or you may cause cracking/dissolving. Try it and see.

If you are using Testor's balsa cement, Ambroid, or similar, those won't work with most plastics.

You need an appropriate solvent glue for some plastics.

Gorilla Glue (the stuff that foams) will hold a wide range of plastics, some that CA won't, but not all..

Jeff Anderson
Livonia, MI
Thanks, Jeff,
Solvent glue (specific to the type of plastic) will get the strongest bond. But Gorilla glue works fine with acrylic; regular CA's not bad; the black CA (w/ rubber nanoparticles) works a little better; all should be plenty strong.
Kenshi Takahashi wrote:
baker wrote:
Kenshi Takahashi wrote:When the rules say the tower must span a 20x20 cm hole, does it mean that the tower's base must have minimum dimensions of 20x20 cm, or that it simply needs to cross the 20x20 gap?
You can rotate a 4 legged tower so you hit the center line (10 cm) of each 20 cm side. A tower base around 15 or 16 cm square should work.
Oh ok. So is a rectangular base OK as long as it spans the 20 cm gap?


Sure. But why would you not want to go for spanning the 29cm circle (and get the 2kg load credit bonus)??
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Re: Towers B/C

Post by Balsa Man » October 31st, 2016, 4:41 pm

hearthstone224 wrote:Hey sorry for changing the subject, but

1. can I say that the leg itself will have to have

4608/8.91 = 517.17 or greater for the BS of a leg 36'' long?

Then

4608/20.11 = 229.1 or greater?

Then so on until 1/8th interval (which is where I stopped?)

I called this the "safe strength", where if it holds more or equal to this amount, it should theoretically hold the load we want?

I get 4608 because that is the safe threshold for 20% variation, and then the multiplier is what I calculated earlier.

2. This question is pretty weird- But we can't use the glue we use for gluing balsa together, right? We need to buy special glue for gluing plastics together? If so could someone possibly post a link of an example for me to buy? This is for the jig construction.

3. Can someone find me a link for 1/4 plexiglass I need to use for the base?
Link - http://www.professionalplastics.com/PLE ... oCjhnw_wcB
But, as I suggested earlier, you could use 3/32nds on top of a piece of shelf board...

Glue- see prev/above - Jeff's post and my comments

The numbers you're discussing; yes, 4608 is correct with 20% SF included. As to the rest....uh, I'm sorry, but I do not follow or understand where the numbers you're using are coming from

For a B-Div tower

1/2 intervals = 25.77cm. That is 0.281 of 36" 1 over 0.821 squared is 12.63
1/3 intervals= 17.18cm. That is 0.188 of 36" 1 over 0.188 squared is 28.42
1/4 intervals= 12.89cm. That is 0.141 of 36" 1 over 0.141 squared is 50.53
1/5 intervals= 10.31cm. That is 0.113 of 36 1 over 0.113 squared is 78.95
1/6 intervals= 8.59cm. That is 0.094 of 36" 1 over 0.094 squared is 113.69
1/7 intervals= 7.56cm. That is 0.080 of 36" 1 over 0.080 squared is 154.74

The bold/underlined numbers are what you multiply the BS you measure at 36" by to get estimated BS at that bracing interval.
Example- you do 36" pushdown test, get 40grams
40 x 28.42 =(1/3 interval) 1137, nowhere near- bracing at 1/3 intervals won't come close
So, a heavier stick test at 165gr
165 x 28.42 = (1/3 interval) 4690, now we're working- a little over the 4608 you're looking for; 1/3 bracing would work
Back to that stick that tested at 40grams- if you go to 1/6 interval bracing on it - 40 x 116.69 = 4547- very close to 4608 = a stick testing a hair over 40 (like 40.54) will work at 1/6 bracing intervals
Making sense now?
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Re: Towers B/C

Post by baker » October 31st, 2016, 5:31 pm

hearthstone224 wrote:Hey sorry for changing the subject, but

3. Can someone find me a link for 1/4 plexiglass I need to use for the base?
I bought 1/4 inch Lexon from Home Depot this past summer. Lowes also had it. Check any good home center, they should have it. I used a table saw to cut it to shape.

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