Ongoing Contest(Scores)

[havenguy]

Despite all of the arguments about intermediate connections (vertical bracings), I've been doing pretty well this year with intermediates.

My most recent boomilevers:


4/10/13
Mass of boom: 9.3
Mass held: 14.5 kilograms
Efficiency: ~1559

4/12/13
Mass of boom: 8.8
Mass held: 12 kilograms
Efficiency: ~1364

Date: 4/16/13
Mass of boom: 8.4
Mass held: 9 kilograms
Efficiency: ~1071

I think I can get down to 8.8 holding the entire thing by States (in a week and a half), which would give me around 1700. I'm testing another boomilever before we leave, so I'll post results then.

I'm almost certain anything >1200 will get me a medal at PA States, and I'm hoping a 1700 will place me in the top 6 at Nats (assuming we make it, which we may not).

[mrsteven]

I made a boom today and pretested it to 10kg, weighing 8.56g.
It was solid and confident itll hold at least 12+kg at state. Ill give you a final count after state saturday

[Balsa Man]

Good progress; you're making nice headway; very respectable score.
We're going to State Saturday. Our Team 2's boom is almost exactly same weight as your last one; Team 1's is.... lighter.

It's great to see folk in other places working with the tube approach. What sort of specs you running on your tubes? Rolled, or have you figured out another way? Ours are not rolled; made w/ 2 pieces. We're running 5/8" i.d., about 1/32nd wall; about 5.3gr tube weight in the 11.1 boom.

We're using a "rolled" tube. It's 1/16" balsa (there's no 1/32 available locally) wrapped around a 1/2" form. Single bass tension and a laminated balsa mounting block.

With the 1/16, we're running anywhere between 4.2-5.3grams for the tube.

This was a steep learning curve, my daughter wasn't doing boom, but decided to try it out after our team's booms were, ...disappointing...

Our States is next week.

I stole this tube idea from you, so a thank you is in order.

That's not stealing- a scientific community; the scientific process at work; a seed planted, and growing. Thank you for exploring new territory. The....basic physics of a tube are compelling; just a matter of figuring out how to implement
Good luck!

[Balsa Man]

Despite all of the arguments about intermediate connections (vertical bracings), I've been doing pretty well this year with intermediates.

You have, indeed. There are pros and cons to just about everything; its figuring out how to manage the tradeoffs you choose. Hope you get to that 1700

I think I can get down to 8.8 holding the entire thing by States (in a week and a half), which would give me around 1700. I'm testing another boomilever before we leave, so I'll post results then.

I'm almost certain anything >1200 will get me a medal at PA States, and I'm hoping a 1700 will place me in the top 6 at Nats (assuming we make it, which we may not).

You have, indeed. There are pros and cons to just about everything; its figuring out how to manage the tradeoffs you choose. Hope you get to that 1700!

[Wolverine]

I've been thrown on boomi and was wondering how to make a good boom that can hold everything. I just built one that was like .1 kg and it held everything putting me in a decent place for states. But has anyone made anything less than .1?? Seems like it would be to unstable to hold anything.

[iwonder]

There's a lot of discussion on the boomilever topic(not this one) about how to lighten booms, but I'd start by going over the wiki and Aia's guide(there's a link at the bottom of the wiki). By the way, boomilever masses are measured in grams, so did you really mean a 100g boomilever? It's definitely possible to go lighter than that. I have a 16g boomilever that's held full load multiple times and other booms that have held but are a lot lighter.

[GeorgeInNePa]

"Tube" Boomilever

First try:
Boom weight-10.95g
Held-7714g
Efficiency Score- 704.5
Mounting block failure.

Second try:
Boom weight-12.25
Held-11316g
Efficiency Score-924
Tube failure due to alignment issues.

Third try will be under 12g and will hopefully hold more. We are learning with each build.

Third try (the boom from the first try with a new mounting block):
Boom weight-11.08
Held- 11512g
Efficiency Score- 1038.99
Tube failure.

Fourth try:

Boom weight- 11.46g
Held- 12069
Efficiency Score- 1053.14
Tube failure, in a way which you would expect with a tube in compression.

I "think" we can get this design over 1100, but not too much higher. We can remove a bit more weight, maybe get it down to 11.0g, but since we don't have a lot of time this is what it is.

I think that the weight held should actually be a bit higher, since we are using very large aquarium gravel and it takes a lot of time to get the weight in the bucket. A sand dispenser like they use at the larger events would allow more weight to be transferred before tube failure.

[Balsa Man]

You may not have time to play with it, but I suspect the tube failure wall you're running into is because of diameter.
Buckling strength is E x I
E is the modulus of elasticity

I =pi/4 (ro^4-ri^4)
(Ro is outer diameter, Ri is inner diameter).
When you run the numbers, that diameter is a significant factor; going from 1/2 inch to 5/8 makes a significant difference (why we went w/ 5/8ths). Lower density at 5/8ths will get you more strength than hi density at 1/2.... It's just the way the numbers work.

[GeorgeInNePa]

You may not have time to play with it, but I suspect the tube failure wall you're running into is because of diameter.
Buckling strength is E x I
E is the modulus of elasticity

I =pi/4 (ro^4-ri^4)
(Ro is outer diameter, Ri is inner diameter).
When you run the numbers, that diameter is a significant factor; going from 1/2 inch to 5/8 makes a significant difference (why we went w/ 5/8ths). Lower density at 5/8ths will get you more strength than hi density at 1/2.... It's just the way the numbers work.

I agree, but my options were 1/2" and 3/4" (leftover copper pipe from a plumbing project). When I go to 3/4, the distal end block becomes way too heavy.

What did you use for a form that has a 5/8" diameter? (if you don't mind sharing just a bit more )

[Balsa Man]

You may not have time to play with it, but I suspect the tube failure wall you're running into is because of diameter.
Buckling strength is E x I
E is the modulus of elasticity

I =pi/4 (ro^4-ri^4)
(Ro is outer diameter, Ri is inner diameter).
When you run the numbers, that diameter is a significant factor; going from 1/2 inch to 5/8 makes a significant difference (why we went w/ 5/8ths). Lower density at 5/8ths will get you more strength than hi density at 1/2.... It's just the way the numbers work.

I agree, but my options were 1/2" and 3/4" (leftover copper pipe from a plumbing project). When I go to 3/4, the distal end block becomes way too heavy.

What did you use for a form that has a 5/8" diameter? (if you don't mind sharing just a bit more )

As I mentioned, we're not using a form - not rolling. I'll say at this point, tubes are machined in 2 pieces (from 1" x 1/2") using a router...
Wall thickness is set by the two bits used