Bridge B/C

[knightmoves]

The interpretation proposed by dholdgreve here would require the bridge cross-section to be something a bit like an inverted 'U'. In both B and C bridges, the pass-thru block height is 3cm smaller than the minimum height of the load block, which would mean that, for a C bridge, you'd build something with a cross-section like a 15cm-high inverted U, with bracing only in the upper 3cm to make the corners rigid.

That's clearly a much heavier device than one that is permitted to use tension straps at the base to tie the sides together. It's also worth pointing out that it's nothing at all like an actual "bridge". Actual bridges have a hole to allow the passage of vehicles or people, but do have a road deck on which those things rest.

Any ideas how ES will test 3e? Put the bridge flat on a table and show that the ends make contact? Eyeball?

It's clearly intended to rule out a design that braces itself against the side of the test support - will ES care about a small amount of sag / the corner of a brace that wasn't trimmed off? (Yes, I know the answer to that one - it's "they won't care unless you assume that they won't, in which case they will.")

[scioly2345]

Hey y’all, so happy to be building again. I think the worst part of bridge this year is gonna be the mandatory large empty space in the middle for the block (for B it’s a little more manageable) and similar to the front of boomis splitting apart, what can be done to combat the bridge splitting apart from the sides?

[sneepity]

Wait I'm still so confused about the huge space that's supposed to be on the bottom.
Where exactly is it supposed to go? I thought it just lies in the clearance space between the two loading points. I didn't know it went THROUGH the bottom of the bridge :?

[JonB]

Wait I'm still so confused about the huge space that's supposed to be on the bottom.
Where exactly is it supposed to go? I thought it just lies in the clearance space between the two loading points. I didn't know it went THROUGH the bottom of the bridge

Imagine the space a car/truck/train would actually move through on a bridge. This is the space that needs to stay clear. Or, that is how I understand it (not official..etc...).

[sneepity]

Wait I'm still so confused about the huge space that's supposed to be on the bottom.
Where exactly is it supposed to go? I thought it just lies in the clearance space between the two loading points. I didn't know it went THROUGH the bottom of the bridge :?

Imagine the space a car/truck/train would actually move through on a bridge. This is the space that needs to stay clear. Or, that is how I understand it (not official..etc...).

so you're saying the truss shouldn't have braces on the side there?
or do you mean from the bottom?
:c

[knightmoves]

Imagine the space a car/truck/train would actually move through on a bridge. This is the space that needs to stay clear. Or, that is how I understand it (not official..etc...).

My opinion is that this is what the rules say - that if you imagine a truck of the specified cross-section, it needs to be able to "drive" though the bridge at some height, thus allowing a bridge "deck" holding the sides together at the base. dholdgreve, in this thread, expressed the opinion that the rules mean that the "truck" has to begin in contact with the support block, and travel horizontally until it contacts the other support block, thus precluding anything tying the two sides together at the base. I don't think he's right, but I see how he can read the rules the way he does, and agree that this warrants clarification.

[mklinger]

I hope to have a complete Division B design to share soon, but in the meantime I wanted to take a quick look at one of the things that makes the Division C rules a bit more challenging than just scaling up a Division B bridge, namely the fact that the pass-through block is 7cm wide and the loading block is only 5x5cm.

I took the approach of looking at the simplest design possible, just 2 cross-member support beams. I kept the dimension the same, in this case, 5/32" thick by 10mm tall by 8cm wide, and varied the density to look at strength. The goal was to see what the minimum mass was needed to try and guarantee holding 15 kg.

For those that just want the results, the answer was about 0.45-0.5g per beam.

If you'd like to see the video I made demonstrating how I got that, including seeing some cool footage of stuff breaking at 3000 fps, you can check it out here:

https://youtu.be/nzDV02CiU94

If you're wondering what I'm doing with my channel and a bit of my background, you can check out my introduction video here:

https://youtu.be/-r0UY3RrfCA

and if you're just starting out and want to learn some material basics and how to build a balsa library to use for all your builds, I highly recommend watching this video:

https://youtu.be/bLsTOpmozGI

My plan this year is to start by focusing on Division B builds as those teams typically need the most direct help, and then scale up the design to see what I can do at the Division C level.

Please feel free to reach out to me here or directly if you have any specific ideas for videos or questions.

Thanks!

Marc

[mklinger]

Third time is a charm! On my 3rd build of the season I was able to achieve what I consider a result good enough to share with a wider audience.

My goal was to build a Division B bridge that follows the new rules (as I currently understand them) and have it hold the entire 15 kg. I wasn't concerned too much with the final mass of the bridge at this point.

When you are working through the design phase, it's a good strategy to use fairly conservative (strong/heavy) wood to make sure your design is sound before trying any material optimization.

The final result here was a 9.24 g bridge that held 16.98 kg which would give a competition score of (15000 + 5000 bonus)/9.24 or 2164.5.

That seems reasonable for this early in the season.

You can watch the video where I show and test the bridge here:

https://youtu.be/AX_CNFw0iEw


There is a huge potential to optimize almost every part of this bridge from a material standpoint.

I hope this helps some teams out by giving you a few ideas on how you might approach the build this year.

I'll probably do some work over the next few weeks to see if I can do some basic material optimization with this design. I'll be sure to share any major breakthroughs or significant score increases.

Feel free to reach out to me if you have any questions.

Thanks!

Marc

P.S. At Bernard's suggestion, I also posted this video to the Gallery in the Bridges category. That is a pretty slick way of sharing photos and videos.

[sneepity]

Third time is a charm! On my 3rd build of the season I was able to achieve what I consider a result good enough to share with a wider audience.

My goal was to build a Division B bridge that follows the new rules (as I currently understand them) and have it hold the entire 15 kg. I wasn't concerned too much with the final mass of the bridge at this point.

When you are working through the design phase, it's a good strategy to use fairly conservative (strong/heavy) wood to make sure your design is sound before trying any material optimization.

The final result here was a 9.24 g bridge that held 16.98 kg which would give a competition score of (15000 + 5000 bonus)/9.24 or 2164.5.

That seems reasonable for this early in the season.

You can watch the video where I show and test the bridge here:

https://youtu.be/AX_CNFw0iEw


There is a huge potential to optimize almost every part of this bridge from a material standpoint.

I hope this helps some teams out by giving you a few ideas on how you might approach the build this year.

I'll probably do some work over the next few weeks to see if I can do some basic material optimization with this design. I'll be sure to share any major breakthroughs or significant score increases.

Feel free to reach out to me if you have any questions.

Thanks!

Marc

P.S. At Bernard's suggestion, I also posted this video to the Gallery in the Bridges category. That is a pretty slick way of sharing photos and videos.

Okay maybe it is just me who doesn't do this, but that's such a great idea to first figure out which beams can hold the full 15 kgs, especially with the clearance block rule this year which kinda forces us to eliminate some support on the bottom. Thanks so much for sharing <3

[JonB]

Imagine the space a car/truck/train would actually move through on a bridge. This is the space that needs to stay clear. Or, that is how I understand it (not official..etc...).

My opinion is that this is what the rules say - that if you imagine a truck of the specified cross-section, it needs to be able to "drive" though the bridge at some height, thus allowing a bridge "deck" holding the sides together at the base. dholdgreve, in this thread, expressed the opinion that the rules mean that the "truck" has to begin in contact with the support block, and travel horizontally until it contacts the other support block, thus precluding anything tying the two sides together at the base. I don't think he's right, but I see how he can read the rules the way he does, and agree that this warrants clarification.

I think this video might answer this question once and for all. There are pieces across the bottom connecting the two sides. This video is on the Science Olympiad official YouTube channel. While maybe it is not OFFICIAL, it pretty much is official (in my opinion).

https://www.youtube.com/watch?v=ZELNwoTXA6E