Boomilever B/C

sneepity
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Re: Boomilever B/C

Post by sneepity » February 20th, 2020, 7:19 pm

dholdgreve wrote:
February 19th, 2020, 8:04 am
sneepity wrote:
February 18th, 2020, 7:44 pm
bernard wrote:
February 18th, 2020, 8:27 am

The rules mention "centerline of the chain."
im not really sure what that means, lol :D
I interpret "center of chain" as the same thing as "center of bolt" and measure accordingly. That said, the loading block is 5cm x 5cm with the bolt hole in the middle. The center of the bolt must be a minimum of 40cm from the wall, so to fully support the loading block, the boom must be a minimum of 42.5 cm long. If you choose to go shorter than that and cantilever part of the loading block beyond the end of the boom, that's on you!
thank you!
rip scio 2020 :cry:

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Re: Boomilever B/C

Post by bernard » February 20th, 2020, 7:55 pm

dholdgreve wrote:
February 19th, 2020, 8:04 am
sneepity wrote:
February 18th, 2020, 7:44 pm
bernard wrote:
February 18th, 2020, 8:27 am

The rules mention "centerline of the chain."
im not really sure what that means, lol :D
I interpret "center of chain" as the same thing as "center of bolt" and measure accordingly. That said, the loading block is 5cm x 5cm with the bolt hole in the middle. The center of the bolt must be a minimum of 40cm from the wall, so to fully support the loading block, the boom must be a minimum of 42.5 cm long. If you choose to go shorter than that and cantilever part of the loading block beyond the end of the boom, that's on you!
If the Loading Block is positioned such that the bolt is not vertical, the "center of bolt" to Testing Wall measurement will vary with height. Freedom between the eye of the bolt and S-hook/chain should allow the chain to remain approximately vertical if not obstructed by parts of the Boomilever.
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Re: Boomilever B/C

Post by sneepity » February 20th, 2020, 8:02 pm

bernard wrote:
February 20th, 2020, 7:55 pm
dholdgreve wrote:
February 19th, 2020, 8:04 am
sneepity wrote:
February 18th, 2020, 7:44 pm


im not really sure what that means, lol :D
I interpret "center of chain" as the same thing as "center of bolt" and measure accordingly. That said, the loading block is 5cm x 5cm with the bolt hole in the middle. The center of the bolt must be a minimum of 40cm from the wall, so to fully support the loading block, the boom must be a minimum of 42.5 cm long. If you choose to go shorter than that and cantilever part of the loading block beyond the end of the boom, that's on you!
If the Loading Block is positioned such that the bolt is not vertical, the "center of bolt" to Testing Wall measurement will vary with height. Freedom between the eye of the bolt and S-hook/chain should allow the chain to remain approximately vertical if not obstructed by parts of the Boomilever.
alright, thank you!
rip scio 2020 :cry:

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Re: Boomilever B/C

Post by Tall » February 21st, 2020, 6:51 am

bernard wrote:
February 20th, 2020, 7:55 pm
dholdgreve wrote:
February 19th, 2020, 8:04 am
sneepity wrote:
February 18th, 2020, 7:44 pm


im not really sure what that means, lol :D
I interpret "center of chain" as the same thing as "center of bolt" and measure accordingly. That said, the loading block is 5cm x 5cm with the bolt hole in the middle. The center of the bolt must be a minimum of 40cm from the wall, so to fully support the loading block, the boom must be a minimum of 42.5 cm long. If you choose to go shorter than that and cantilever part of the loading block beyond the end of the boom, that's on you!
If the Loading Block is positioned such that the bolt is not vertical, the "center of bolt" to Testing Wall measurement will vary with height. Freedom between the eye of the bolt and S-hook/chain should allow the chain to remain approximately vertical if not obstructed by parts of the Boomilever.
For division C, I know the max contact depth line is 15 cm from the hook.
Is there a minimum contact depth requirement?
Also, are there any advantages designing a tension boomi with short contact depth distance?

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Re: Boomilever B/C

Post by Torchic » February 21st, 2020, 11:22 am

Tall wrote:
February 21st, 2020, 6:51 am
bernard wrote:
February 20th, 2020, 7:55 pm
dholdgreve wrote:
February 19th, 2020, 8:04 am

I interpret "center of chain" as the same thing as "center of bolt" and measure accordingly. That said, the loading block is 5cm x 5cm with the bolt hole in the middle. The center of the bolt must be a minimum of 40cm from the wall, so to fully support the loading block, the boom must be a minimum of 42.5 cm long. If you choose to go shorter than that and cantilever part of the loading block beyond the end of the boom, that's on you!
If the Loading Block is positioned such that the bolt is not vertical, the "center of bolt" to Testing Wall measurement will vary with height. Freedom between the eye of the bolt and S-hook/chain should allow the chain to remain approximately vertical if not obstructed by parts of the Boomilever.
For division C, I know the max contact depth line is 15 cm from the hook.
Is there a minimum contact depth requirement?
Also, are there any advantages designing a tension boomi with short contact depth distance?
From what I know (talked to some Warren people), there is no minimum. A short contact depth distance decreases the amount of material used on the tension arms and up-and-down crossbracing, but it severely increases the force on the compression arms, making the boomi weaker overall.
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Re: Boomilever B/C

Post by Tall » February 21st, 2020, 2:02 pm

Torchic wrote:
February 21st, 2020, 11:22 am
Tall wrote:
February 21st, 2020, 6:51 am
bernard wrote:
February 20th, 2020, 7:55 pm

If the Loading Block is positioned such that the bolt is not vertical, the "center of bolt" to Testing Wall measurement will vary with height. Freedom between the eye of the bolt and S-hook/chain should allow the chain to remain approximately vertical if not obstructed by parts of the Boomilever.
For division C, I know the max contact depth line is 15 cm from the hook.
Is there a minimum contact depth requirement?
Also, are there any advantages designing a tension boomi with short contact depth distance?
From what I know (talked to some Warren people), there is no minimum. A short contact depth distance decreases the amount of material used on the tension arms and up-and-down crossbracing, but it severely increases the force on the compression arms, making the boomi weaker overall.
Thanks.

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Re: Boomilever B/C

Post by Cornstalk » February 24th, 2020, 12:02 pm

Hello! I was just put on boomilever and came here looking for advice. I have read through the past forums posts (including 2013-2014) and I am still confused on some aspects that I hope you guys can help me with! What gives a higher efficiency, wood that is more dense or wood that has larger dimensions? Also, how effective are tension-compression members and what is the best way to use them (should they be wider, thinner pieces or smaller pieces such as those used for x braces on the compression members)? I have only built one boom so far but I am planning on building another one today and seeing where I can improve. To give some specs about my boom, I used 3/16" bass for the tension members, 3/16" balsa for the compression members, and I had 6 x braces that were 1/8" by 1/16". My booms weighed 11.75g. It broke in the middle of the compression member. The bucket started to sway and and it ripped the compression member in half sideways.

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Torchic
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Re: Boomilever B/C

Post by Torchic » February 24th, 2020, 6:47 pm

Cornstalk wrote:
February 24th, 2020, 12:02 pm
Hello! I was just put on boomilever and came here looking for advice. I have read through the past forums posts (including 2013-2014) and I am still confused on some aspects that I hope you guys can help me with! What gives a higher efficiency, wood that is more dense or wood that has larger dimensions? Also, how effective are tension-compression members and what is the best way to use them (should they be wider, thinner pieces or smaller pieces such as those used for x braces on the compression members)? I have only built one boom so far but I am planning on building another one today and seeing where I can improve. To give some specs about my boom, I used 3/16" bass for the tension members, 3/16" balsa for the compression members, and I had 6 x braces that were 1/8" by 1/16". My booms weighed 11.75g. It broke in the middle of the compression member. The bucket started to sway and and it ripped the compression member in half sideways.
Increasing the density of balsa wood drastically increases the strength. An 1/8" by 1/8" would be stronger than a 3/16" by 3/16" with the same weight because the density in the 1/8" by 1/8" is higher. Last year, I ended up using (forgot the weight) these somewhat dense 3/16" by 3/16". They never broke. However, if you want to use 1/8" by 1/8" pieces for compression members, I recommend using a 2 layered base, since pieces of wood with smaller cross-sections are also weaker. This year, I used a lot of these light 1/8" by 1/8" and got a somewhat decent efficiency (even though it was risky). For tension members, they usually don't have as much force on them as the compression members, so it is fine to go with balsa wood instead to reduce weight. The thing is with the tension arms, you should use a gusset at the attachment site of them to the compression arms. When the tension arms bend when weight is on it (ex: just attaching them if the top is narrow) they break a lot sooner than expected. For the breakage of your boomi, it was probably (well, at least part of) the bucket's fault. When the bucket sways, weight shifts between compression arms, and the force increases sharply on the arm that the bucket is swinging towards. The arm probably had too much force on it, so it broke. When my partner stabilizes the bucket, he always keeps the sticks lightly touching, enough to stop the bucket from swaying, but not so much force as to make the bucket sway on its own.
Hope this helps!
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Re: Boomilever B/C

Post by MadCow2357 » February 24th, 2020, 7:49 pm

Torchic wrote:
February 24th, 2020, 6:47 pm
For tension members, they usually don't have as much force on them as the compression members, so it is fine to go with balsa wood instead to reduce weight.
It is true that the tensile force is slightly less than the total force exerted on a compression boomilever, but the huge variations in balsa are often impossible to predict even if you weigh and choose each stick carefully. This is why most people are using basswood for tension members, because of its greater consistency. You are taking a significant risk by building with balsa tension members imo
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Re: Boomilever B/C

Post by Torchic » February 25th, 2020, 6:26 am

MadCow2357 wrote:
February 24th, 2020, 7:49 pm
Torchic wrote:
February 24th, 2020, 6:47 pm
For tension members, they usually don't have as much force on them as the compression members, so it is fine to go with balsa wood instead to reduce weight.
It is true that the tensile force is slightly less than the total force exerted on a compression boomilever, but the huge variations in balsa are often impossible to predict even if you weigh and choose each stick carefully. This is why most people are using basswood for tension members, because of its greater consistency. You are taking a significant risk by building with balsa tension members imo
Ah, I forgot to mension that we specifically test every single stick we get. Yea, balsa wood is really bad when it comes to that. We can have 2 sticks of the same weight, and they may both seem good, but one stupid stick has this giant air bubble in the middle. To make sure we don't mess up the boomilever that way, I set up a chart that calculates how strong the balsa wood member should be under tension/compression based on the weight, density (I order specific sticks based on density), and cross-sectional area. I test the sticks in a weight test (it figures out if the 2 halves of the stick are similar in weight-if they are not, its likely that theres a problem with the wood), a compression test (needs to reach a specific amount of grams when you push down), a bending test (I bend it gently-if the bend is not in the center, the wood has some irregularities), and a tension test to see if one half of the stick is stronger than another or to check if the tension is stronger in one way than another.
Last year, we almost never had a compression break-it was always the tension arms. We realized after 3 competitions that it was breaking because of: a) bad glue joints, b) stupid paint on the end of the wood for marking it weakened it a LOT, and c) we really sucked at getting good tension arms. Also, with balsa wood, the higher the density, the less of a chance that the wood will have irregularities, so we use decently dense tension arms (1.8? g/stick for 1/8" by 1/8"), and we have yet to see a failure in those.
EDIT: We also use balsa wood because the place in where we order balsa wood doesn't have bass wood, and we never tested with bass either. The balsa wood usually breaks near the joints (Ex: near the top or near the bottom attachment site). We figured out how to counter that, even though it takes some effort and a lot of testing/breaking weak tension arms.
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sneepity (March 15th, 2020, 8:15 am)
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