Boomilever B/C

[museicorn]

Hey, so Im just wondering what you guys think. For the mounting base of the boomilever do you think that area should be compromised for lightweight or vica versa? Thanks

[Balsa Man]

Thanks guys! I have a few more questions:

1. The rules say the Testing Wall needs to be at least 40.0 cm wide. Then it says the middle mounting hole must be centered on the wall, and the centers of the other holes placed 10 cm from the center of the middle hole. Does this mean the distance between the middle hole and a side hole is 10 cm, and the distance from one side hole to the other side hole is 10cm? Because if the distance between the center hole and the other side hole is 10cm, the Boomilever would be pretty big..

2. On the Boomilever Wiki Page, it says:
According to the esteemed Bob Monetza: "You'd want to get the point of support as close as possible to the center of the block. If the center of the block is beyond the connection point between the tension and compression chord, it will cause bending of the compression chord, like a diving board."

I understand that if the block is beyond the connection point, the compression chord would become weaker. Then if this is known, why did these boomilevers have the block beyond the connection? Wouldn't it be better to have it before the connection point?
http://scioly.org/phpBB3/gallery/image_ ... ge_id=1356
http://scioly.org/phpBB3/gallery/image_ ... ge_id=1348
http://scioly.org/phpBB3/gallery/image_ ... ge_id=1355

Erm... http://www.scioly.org/phpBB3/viewtopic.php?f=147&t=3876

Uh, this link is about how this forum is not for official rules clarifications. Noobforce's Q1 is really .....just a misunderstanding, vs needing/asking for any official clarification. There are 3 holes- one in the center, and one on either side. The side holes are 10 cm from the center hole, so they are 20cm apart. You can hook the boom up on one, or two, or three if you want. Simple as that.
Q2 is clearly a design question, having nothing to do with any rules clarification. Quick answer on why the booms shown had the configuration they did - because they did. Just because there is a posted picture doesn't mean the design was good/successful. Better to have T-memb connection past the block center? that would also induce bowing in the compression member; as Bob is correctly quoted, "support as close as possible to the center of the block" is what you need to minimize bending forces. The compression member has to carry the axial compression load put on by the sand bucket (~40kg in a C-boom, ~30kg in a B-boom with 15kg inthe bucket). If there are forces bowing it, it has to carry/control the additional force, i.e., has to be heavier...

[noobforce]

Thanks guys! I have a few more questions:

1. The rules say the Testing Wall needs to be at least 40.0 cm wide. Then it says the middle mounting hole must be centered on the wall, and the centers of the other holes placed 10 cm from the center of the middle hole. Does this mean the distance between the middle hole and a side hole is 10 cm, and the distance from one side hole to the other side hole is 10cm? Because if the distance between the center hole and the other side hole is 10cm, the Boomilever would be pretty big..

2. On the Boomilever Wiki Page, it says:
According to the esteemed Bob Monetza: "You'd want to get the point of support as close as possible to the center of the block. If the center of the block is beyond the connection point between the tension and compression chord, it will cause bending of the compression chord, like a diving board."

I understand that if the block is beyond the connection point, the compression chord would become weaker. Then if this is known, why did these boomilevers have the block beyond the connection? Wouldn't it be better to have it before the connection point?
http://scioly.org/phpBB3/gallery/image_ ... ge_id=1356
http://scioly.org/phpBB3/gallery/image_ ... ge_id=1348
http://scioly.org/phpBB3/gallery/image_ ... ge_id=1355

Erm... http://www.scioly.org/phpBB3/viewtopic.php?f=147&t=3876

Uh, this link is about how this forum is not for official rules clarifications. Noobforce's Q1 is really .....just a misunderstanding, vs needing/asking for any official clarification. There are 3 holes- one in the center, and one on either side. The side holes are 10 cm from the center hole, so they are 20cm apart. You can hook the boom up on one, or two, or three if you want. Simple as that.
Q2 is clearly a design question, having nothing to do with any rules clarification. Quick answer on why the booms shown had the configuration they did - because they did. Just because there is a posted picture doesn't mean the design was good/successful. Better to have T-memb connection past the block center? that would also induce bowing in the compression member; as Bob is correctly quoted, "support as close as possible to the center of the block" is what you need to minimize bending forces. The compression member has to carry the axial compression load put on by the sand bucket (~40kg in a C-boom, ~30kg in a B-boom with 15kg inthe bucket). If there are forces bowing it, it has to carry/control the additional force, i.e., has to be heavier...

Ohhhh, thanks, I understand everything now! Time to get to work on my Boomilever!

[XXiggy_gimXX]

Hey, I am wondering, does anyone know if round/cicular designed are good for a boomilever? What I mean is making the boomilever a semi-circle or something. I know making it will be hard, but I am trying to think out side the straight sticks of balsa wood glued together.
Thanks

[Balsa Man]

Hey, I am wondering, does anyone know if round/cicular designed are good for a boomilever? What I mean is making the boomilever a semi-circle or something. I know making it will be hard, but I am trying to think out side the straight sticks of balsa wood glued together.
Thanks

The short answer to your question is no, but let me take a few minutes to give a long answer as to why, and some thoughts to help guide thinking about how get to good ideas.
Remember, The First Rule for any event, before rule #1 for an event, is read the rules until you know and understand what they are and say.

First, and very importantly - being open to thinking “outside the box” is a good thing! That’s where real breakthroughs come from.
Kudos to you for doing that.

Second, to get to a breakthrough from thinking outside the box, what are sometimes referred to as “critical thinking skills” are also required – how to think through a problem, and get to a workable, a “good”, and perhaps a new, or “the best” solution.

Before talking more about that- a couple comments on your question – is a round/circular design “good?” I think/assume you mean do well competitively- not necessarily win, but be competitive (within the limits of the time and effort you’re willing and able to put into the event) – be better than what some, or most folk do.
Scoring, the measure of how “good” what you do is, is based on pure structural efficiency- the load carried, divided by the weight of the structure. That could be the lightest structure you can build that can carry the maximum load (15kg), or a significantly lighter structure that carries the same or better proportion of the load- e.g., half the weight that carries half (or a little more than half) the load. This scoring is for booms that meet both the “construction” and “competition” rules; booms that don’t are scored in lower “Tiers” behind all booms that meet these rules (Tier 2- competition violation- e.g., you take more than 10 minutes; Tier 3- construction violation- e.g., it doesn’t hold the block at least 40cm from the wall). A boom that weighs 10 pounds, meets the construction specs, and carries the weight of the empty load bucket beats a boom that violates either the construction or competition rules. Behind everything are booms that can’t be loaded. So, to meet your criterion of “good”, we’re talking being in Tier 1.

So, let’s look at the critical thinking process, and the idea you’re exploring/wondering about….

At it’s essence, “critical thinking” is a “screening” process- an iterative sifting through ideas; dropping those that “just won’t work”; getting down to what will work, and then to what will work best. There are a lot of ways this could be described- we could get off into all kinds of discussion/side tracks; different folk would see and describe it differently. Here’s one cut at it.
What is the problem?
What are the constraints?
What are the possibilities that fit the constraints?
Then, looking at such possibilities either collectively or individually- is there a better way?
Circle back to, what are the constraints?
How do you optimize (theoretically)?
How do you actually do it (jumping from the theoretical to practical reality)- with the resources you have, can you translate theory to constructed reality?.

Focusing this now to the case of building an S-O boomilever:

What is the problem?:
This is broadly, but very clearly stated in the first sentence in the rules- Rule #1; “The objective of this event is to design and build the most efficient boomilever meeting the requirements specified in these rules.”
Distilling this down to ‘physical reality’; it can be re-stated as, “how do you build a light/efficient structure that holds a load block 40cm away from the testing wall (that is 40cm wide by 30cm high), that is connected to the wall by one or more bolts, and that doesn’t touch the wall more than 20cm (for a B-division boom) below the line of the bolt(s)?”

What are the constraints?
Obviously, the first level of constraints is the rules; what can you do, what can’t you do.
There is a “what can you use?’ constraint- wood and glue. One could build a carbon fiber boom that could hold full load, and be significantly lighter than what will win Nationals, but it would be scored in Tier 3 (construction violation)
Then there are what can be described as “geometric” constraints- how things have to fit within a set of measurements that are defined in the rules.
-has to hold the (center of) the load block 40cm from the wall,
-has to be attached to one or more of the bolts (which are on a line 5cm below the top of the test wall
-has to touch the test wall (which is 40cm wide, and 30cm high), and it can’t touch the test wall more than 20cm below the line of the bolts

The next level would be what can be described as strength/physics/engineering constraints – what forces are at work on the pieces; are they strong enough to carry those forces; are there ways to make them lighter, yet still carry the forces at work. In it’s simplest form, that means a piece (or pieces) under tension loading about 33kg for a B-boom at a full 15kg bucket weight), attached to a bolt or bolts, and extending down to, and attached to another piece, or pieces that will be under compression loading (about 30kg for a B-boom at a 15kg bucket weight)

What are the possibilities that fit the constraints?
So, can a semi-circle fit the geometric constraints? The answer seems no, for the following reasons
To hold the block 40cm from the wall, a semi-circle would have to have a radius of a bit over 40cm- a diameter of 80+cm.
It would have to be able to be in contact with the testing wall. The 30cm high by 40cm wide minimum (“at least”) dimensions are what you have to figure on. The wall can be bigger, but event supervisors are only required to meet the minimum. For both cost of materials, and ease in hauling around, they’re unlikely to go much bigger, and VERY unlikely to go more than twice the minimum requirements. So, a semi-circle with the ends 80+ cm apart won’t even come close to having both ends in contact with a 30x40 wall, no matter how you orient it. You could build/use a big enough wall to support such a shape, but if you brought that boom to a competition, that would put you in Tier 4

Even if it were to fit, your observation of “hard” to build would come into play- circles and arcs of circles- and other curves in some cases, have…..wonderful structural properties. The problem is one of precision; if sections of the arc/curve are straighter than, or more curved than the “design curve”, the strength falls of dramatically; you get weak points/premature failure points. Getting wood bent to precisely fit an intended curve is VERY hard

So, in thinking this all through, remember, “form follows function”- understand the forces at work; figure out the lightest way to build something that can handle those forces; figure out how to build with enough precision that you’re not introducing additional unexpected forces (like twisting).

Take the time to read through the pages of this event thread- lots of good ideas, insights, discussions. Look at the gallery to see how others have approached this.

Lots of words, lots of things to think about, lots of places where thinking outside the box just might find an idea that is “good”; that will get you to a more efficient structure. Hope this helps you- and others- in that process.

[flyingwatermelon]

Does anyone have any recommendations or plans for building a testing rig? I'm planning to install a testing rig on the side of my garage but that involves nailing the rig to the beam of the house. I am sure there is a better solution to this, does anyone have ideas?

[jma]

If the distance from the face of the testing wall to the center of the loading block is at least 40 cm, does that mean that i have to build the boomilever at least 42.5 cm long?

[Balsa Man]

If the distance from the face of the testing wall to the center of the loading block is at least 40 cm, does that mean that i have to build the boomilever at least 42.5 cm long?

Well, you have to support the load block, so 40cm + 1/2 of 1/4" (the eyebolt thru the load block), and then enough to support the load block beyond the eyebolt hole. Does that have to be the full 2 1/2cm beyond the center of the load block? No, it's really a judgement call how much you need.

[Balsa Man]

Does anyone have any recommendations or plans for building a testing rig? I'm planning to install a testing rig on the side of my garage but that involves nailing the rig to the beam of the house. I am sure there is a better solution to this, does anyone have ideas?

Attaching with screws would make it much easier to take down when you're done...

[flyingwatermelon]

Does anyone have any recommendations or plans for building a testing rig? I'm planning to install a testing rig on the side of my garage but that involves nailing the rig to the beam of the house. I am sure there is a better solution to this, does anyone have ideas?

Attaching with screws would make it much easier to take down when you're done...

Well I was thinking of a transportable testing rig that didn't have to be installed to a wall.