Boomilevers 2019 (B/C)

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Re: Boomilevers 2019 (B/C)

Postby retired1 » June 8th, 2018, 2:19 pm

https://scioly.org/wiki/index.php/Boomilever
Here is a good place to start.

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Re: Boomilevers 2019 (B/C)

Postby Unome » June 8th, 2018, 3:39 pm

pajobubo wrote:I’m confused about how we have to build the boomilever so it can attach to the wall. Or I guess what the little piece to attach to wall looks like. Can we just google the rules from past or do you guys just have them?

As of the 2014 switch to a hook rather than a bolt, the top part is typically a rod parallel to the wall which just hangs onto the hook. The bottom part rests against the wall freely.
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Re: Boomilevers 2019 (B/C)

Postby MadCow2357 » June 25th, 2018, 1:34 pm

So what type of wood are you guys going to use for your mounting pieces?
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Re: Boomilevers 2019 (B/C)

Postby dholdgreve » June 26th, 2018, 10:29 am

MadCow2357 wrote:So what type of wood are you guys going to use for your mounting pieces?


I think that will totally depend on what they come up with as a means of attachment. In years past, we have done both laminated flat bases that bolt to the vertical wall, and non-laminated dowels that hook behind the eye hook. In both cases, we used medium to dense balsa.
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Re: Boomilevers 2019 (B/C)

Postby TheChiScientist » July 1st, 2018, 7:02 pm

dholdgreve wrote:
MadCow2357 wrote:So what type of wood are you guys going to use for your mounting pieces?


I think that will totally depend on what they come up with as a means of attachment. In years past, we have done both laminated flat bases that bolt to the vertical wall, and non-laminated dowels that hook behind the eye hook. In both cases, we used medium to dense balsa.

I agree. Balsa will be my first try but I'll most likely go bass.
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Re: Boomilevers 2019 (B/C)

Postby retired1 » July 2nd, 2018, 12:42 pm

Note that heavy balsa and basswood have about the same tensile strength. Quality of the wood will be a major difference. All balsa and all basswood have won in the past.

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Re: Boomilevers 2019 (B/C)

Postby triangulator » July 2nd, 2018, 5:44 pm

I have started (and possibly finished) two boomilever prototypes (ie ones that may not exactly fit length reqs by maybe 2 cm.) Do u think it is better to go with the simple, basic design, or the triangular pyramid design? I think the latter of my two is much lighter+stronger. :idea:
As for wood, i guess u could say im in the 'elite', 'cause i use both woods.
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Re: Boomilevers 2019 (B/C)

Postby retired1 » July 2nd, 2018, 8:46 pm

What are you calling a simple basic design and what are you calling a pyramid design. PM me a sketch with dimensions of both and I will put it on my 3D computer program. Also wood weights per CF of each. prefer lb/cf

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Re: Boomilevers 2019 (B/C)

Postby triangulator » July 3rd, 2018, 7:50 am

I will get back to u on that, just give me a few. As for the simple design, just look at the wiki. Mine is basically that, but with very thick compression and thinner basswood tension pieces. For the triangular pyramid, it's literally a triangular pyramid with two right triangle faces, one acute/isoceles face. My cross bracing is INCREDIBLY complicated and i dont want to draw it. its summer vacation. If u don't know what one of those looks like, i can't help u. look it up. Also, i am informally building, so i haven't actually drawn these designs up. :D i have not checked my wood weights, as it is not reg. season and im not actually using these in comp. im only div. B dude.



On a different note, it weighs a bit north of nine grams, and should get an efficiency of ~1200???? Haven't tested.

What do u guys thing a winner would look like??? What would its score be?
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Re: Boomilevers 2019 (B/C)

Postby windu34 » July 3rd, 2018, 11:24 am

triangulator wrote:What do u guys thing a winner would look like??? What would its score be?

Looking at 2014 Nationals scores for Boomilever:
1: 2322
6: 1469
10: 1294
Obviously the rules are different, but you can probably get an idea by looking at the 2014 rules parameters/dimensions and predicting if you think efficiencies will be higher or lower. I don't personally have much experience with Balsa so I won't try to make any predictions, but I'd be interested to hear someone who does have experience try to make a prediction.
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Re: Boomilevers 2019 (B/C)

Postby MadCow2357 » July 3rd, 2018, 1:29 pm

Umm quick question, I was looking at the Boomilever wiki, and I read this:

balsa wood is better at compression then tension.


I remember Balsa Man (May he rest in peace) and a couple of others talking about how balsa wood is much better in tension than compression last season (2017-2018). So after seeing that on the wiki... I'm kind of confused...

Is balsa wood better at tension than compression, or is it the other way around?
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Re: Boomilevers 2019 (B/C)

Postby retired1 » July 3rd, 2018, 3:50 pm

Any material is better in tension than in compression. I think that the main reason is that it can buckle in compression but it cannot in tension.
For boomilever, you need to have good joints when in tension.
For a brace that is in compression, something like a square cross section is the best for a given weight of balsa. For a brace in tension, I like to use a thinner-wider piece for better gluing strength.

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Re: Boomilevers 2019 (B/C)

Postby randomperson123 » July 3rd, 2018, 4:37 pm

I competed in boomilever back in middle school and was typically getting 1300-1400 with a "normal" boomilever design, the score dropped to about 1200 at States, but it was still much higher than 2nd place. The score dropoff that Windu mentioned at nationals was also similar to most state competitions, though not as drastic. Hopefully, there are changes to the rules to make the event a little more interesting and competitive at the state and regional levels as there was pretty big learning curve for boomilever that wasn't really there for towers or bridges. Boomilever was a fairly complex problem the first time around so I'm hoping there's a twist this year and not just the standard boomilever rules.

As for winning scores, it really depends on what changes there are to the rules, though based on the trend for bridges/towers, the first year in rotation has been a standard structure with a significant change the second year. If the rules stay the same as 2014, I think scores at nationals will have a similar dropoff with a few teams possibly scoring much higher than the rest. Scores might be higher in general though as there are probably other people like myself who competed in boomilever in Div B and are now in Div C.

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Re: Boomilevers 2019 (B/C)

Postby triangulator » July 3rd, 2018, 7:09 pm

What design would u recommend? simple or trianglular?? also, if triangular, how would u support the bolt?

And one more thing: r u guys div B, C, or grad? This is my first boomilever stuff, but it seems that with the stuff u guys r saying im okay at it.
in my opinion, this is like 50% easier than towers.
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Re: Boomilevers 2019 (B/C)

Postby randomperson123 » July 4th, 2018, 3:42 pm

triangulator wrote:What design would u recommend? simple or trianglular?? also, if triangular, how would u support the bolt?

And one more thing: r u guys div B, C, or grad? This is my first boomilever stuff, but it seems that with the stuff u guys r saying im okay at it.
in my opinion, this is like 50% easier than towers.


To clarify, I'm in Division C, but I competed in Boomilever 4-5 years ago when I was in Division B. The difference between div B and C was fairly standard. Div B had 5 cm of extra height to work with, one of the major factors in the strength of cantilever bridges.

When I competed, I only used the standard boomilever style, though that's probably because I've never seen what a triangular prism boomilever looks like. However, it does seem as though there are references to this design in the 2014 boomilever forums (haven't found pictures yet though).

Trying to compare the easiness of towers and boomilever is fairly trivial. Boomilever is much easier to construct as every joint is flat and flush 90 degrees unlike towers, where issues in construction will be the primary downfall.

However, as someone who enjoys designing more than the actual construction of structures, I have mixed opinions on both events.

Towers:
- All competitive towers basically look the exact same, so its really easy to start off with a good efficiency.
- The forces that act on a tower are extremely simple, so its extremely easy to calculate the forces on certain parts of the tower, making it extremely easy to modify designs with consistent increases in efficiency.
- long build time, around 5-6 hrs for this years competition, 3-4 hours for 2016-2017
- I typically only changed bracing patterns once I found the optimal measurements to barely pass the bonus circle and 8cm circle, so I only had to build one jig.

Boomilever
- Because boomilever does have a relatively more complex group of forces acting on it, it is much harder to come to a conclusive "optimal"
design, which results in people coming up with drastically different solutions and with different types of wood.
- I changed the general structure and measurements of the compression chord fairly frequently, so I had to make a new jig for each fundamentally different design. (On some designs I experimented with would thicker than 1/8 x 1/8)
- much simpler to construct, while proper construction techniques are crucial (joints), not as much effort is required to ensure a good build.
- definitely much less build time around 2-3 hrs for a competition boom
.


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