2023 Science Olympiad Bridge Div B: Getting Started

[@unquiet3015]

I appreciate your help so much. I recently tested my bridge using your desgin, and it held 15 kg while weighing 5.27 grams, earning me a score of 3795.

[@balsaengineering6686]

Congratulations! That is a fantastic result, great job!

[@creatifminds]

Hey, your videos are super helpful, and I have a question, what glue do you use or recommend using?

[@balsaengineering6686]

Thanks! The short answer is I like to use 50 cps CA glue for these builds. I actually made an entire video on glue and gluing techniques you might find useful: kzbin.info/www/bejne/a2bPk2WBr7icrck

[@lznachowski]

Hi! Very informational video, thank you! In the video you state you used a sheet of 1/8 thick balsa. Can you link directly to the sheet you used? Thank you!

[@balsaengineering6686]

Hi, thanks for the positive feedback! I would have bought that sheet with a bunch of others from Specialized Balsa. I like getting the 4" wide x 36" long sheets. Here is their order page: specializedbalsa.com/products/balsa_sheets.php I don't think I mentioned it directly in the video, but that entire sheet weighed 31.97g. You can see the markings at the ~4:01 point in the video. To get a sheet that light, you might have to order "light" balsa from Specialized Balsa. Good luck!!

[@geniusiqplays9803]

First of all, thank you so much for helping me build a good bridge for science olympiad competitions. Could you please tell me what size wood you usually use for the cross-braces, and the tension pieces on the bottom if I want to target a score of 4500? I will probably use 1/8 inch wood for the rest of the bridge though. Thank again.

[@balsaengineering6686]

Thanks for the kind words! For the cross bracing, I like to use 1/20" thick balsa and cut it square to around 1/20". For the primary tension pieces, I like to use 1/32" x 1/16" basswood. Good luck!!

[@unquiet3015]

These videos have helped me and my brother so much, and I thank you. My brother got 1st in bridge in an invitational for division C, and I just finished my 3rd try at making this bridge and got a 2400 score. To be fair, I could have made it lighter since it held all the sand we had, which was 18.3 kg; it would have probably been able to hold more, but who knows.

[@balsaengineering6686]

Thanks for the kind feedback! It sounds like you and your brother are doing a great job so far, keep it up!

[@kromydas5063]

15 kg is all you need to hold for Div B, so you definitely make it less heavy. If you had too many x-braces(like me), you could trim it down

[@macferigo]

These videos are so great. Thank you so much for all your information. I have a silly question, has anyone ever tried to build a bridge by bending balsa wood to create an arch ?

[@balsaengineering6686]

Thanks for the kind feedback! It is possible to build an arch bridge with balsa, but from what I understand it involves getting the material wet/soaked and then bending it in place with a jig. Even if it could provide some benefit over an optimal conventional bridge, which I'm not sure it can, the hassle involved really wouldn't be worth it IMHO. One of the keys to success for this event is to have as simple a build as possible so it is as repeatable as possible. Making an arch bridge would be pretty much the opposite of that. Also, a perfect arch design would still need a way to support a flat loading block for these rules, so that would also cause a headache with the design. All that being said, it might be fun to try at some point!

[@macferigo]

@@balsaengineering6686 thank you so much for your reply. My train of thought was the arch would spread the weight evenly throughout the structure. But the loading desk might be a problem for sure.

[@balsaengineering6686]

@@macferigo Because we're able to work with basically a triangle bridge, the loading is already well distributed across the legs. Compared to a conventional "road-bridge", an arch design would have a big advantage. But that is also why these triangle bridges have a big advantage as well as we can design them for essentially a point load in the middle instead of a distributed load across the entire structure (like a real bridge).

[@sibaiyan]

Is there a good alternative to using a balsa stripper? Our team doesn't have one.

[@balsaengineering6686]

I would consider it one of the essential tools unless you are going to buy all your balsa pre-cut. That will be much more expensive than just buying one of these for < $20: www.amazon.com/Master-Airscrew-Windsor-Propeller-Stripper/dp/B0000WS5OQ/ref=sr_1_1?crid=81NEVH3R3DFB&keywords=balsa+stripper+master+airscrew&qid=1680907510&sprefix=balsa+stripper%2Caps%2C172&sr=8-1 If you are in a pinch, I suppose you could use an X-acto knife and something like a metal ruler or other straight edge to guide the cut, but I wouldn't recommend that

[@sibaiyan]

@@balsaengineering6686 Thanks, also what would be a good efficiency for a bridge that is in states?

[@balsaengineering6686]

@@sibaiyan Hi! It's really hard to tell as there will be a huge range between different states. In some states, 4000 could win, in some with strong build teams, it might take 6000+ to win.

[@sunithagundam3452]

Can you please share the balsa wood pieces sizes you used?

[@balsaengineering6686]

I think I talk about the sizes of everything I used throughout this video. Is there a specific question you have that isn't covered in the video?

[@sunithagundam3452]

@@balsaengineering6686 it is 1/16*1/32? I git confused with the bottom piece size?

[@balsaengineering6686]

@@sunithagundam3452 For this particular build, it was 1/8 x 5mm balsa, but what I recommend is 1/16 x 1/32 basswood

[@sunithagundam3452]

@@balsaengineering6686 thank you for the response, for the side part can I use 3/32, are any other better recommendations?

[@balsaengineering6686]

@@sunithagundam3452 Yes, my recommendation is to use 3/32 thickness for the legs. 1/8" is also a good choice, but I like to use 3/32 for most builds

[@shilpasail6693]

@Balsa Engineer I was trying to find the graphing paper you used in the video but can't seem to find it. Can you please tell me?

[@balsaengineering6686]

Hi! Here is the link to the 17x22 graph paper I've been using: www.amazon.com/gp/product/B000HF6ZS4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1 if you are only worried about the Div B dimensions, you can probably just get the 11x17 size

[@silencerko48]

Hey! I made my first bridge for division c using your help. My bridge weight 12.33 grams and held 14.14 kilograms because the main leg of the design failed due to a cutting error on my end that I didn't notice until looking back at a picture of when I first finished the bridge. I'm looking to improve my design and see where I can improve on. To do that I was hoping to build a testing platform. I was wondering what material you used for the loading block and test supports.

[@balsaengineering6686]

Hey! Congratulations on your build! That is a really nice result for a first attempt! As for the loading block and test supports, you can use any kind of wood. Hard woods like oak/maple are probably better to use than pine. I inherited my loading blocks, so I didn't make them myself. For the test supports, I just 3D printed them. You could also 3D print your loading block too, that might be a very good way to go especially if this is just for your personal testing platform. Good luck!

[@jqxz230]

How do you set up the dry box? My box was not completely air-tight and after the first bridge, the silica get has saturated, and new bridges no longer dry in the box. Do you use new gel for each bridge, or make the box you store the bridge in airtight?

[@jqxz230]

I'm looking at either replacing the gel each time, baking it to remove the water, or attempting to make the box air-tight (although I'm not sure how I'll do the last one)

[@balsaengineering6686]

Nothing too special, but you need to make sure your bin is as air-tight as possible. Make sure the top has a foam seal or you'll never have a chance. A single set of silica gel packs should last for weeks if it's done right. One recommendation would be to get some cheap humidity meters and tape one inside your box and compare it to the outside RH. That way you'll know if your dry box is working well. I'm using these: www.amazon.com/gp/product/B07GNMKYCZ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 Your inside the dry-box RH should be 20% or less if things are working well.

[@balsaengineering6686]

@@jqxz230 Don't bother baking your bridge. If you don't have a perfect dry-box to transfer it into immediately, you'll lose everything the baking does in a matter of minutes. A simple plastic bin from Target can be almost air-tight if the top has a foam seal. Look for that when you pick one up.

[@chillslip4714]

Hello, I am writing in regards to the dry box you used for the weight loss. Where can I find/buy the dry box you used ?

[@balsaengineering6686]

Hi! I made an entire video on the process of using the dry box and how/why it works. Check out this video: kzbin.info/www/bejne/bKuyp3uDj7GUhKc I usually buy the bins at my local Target or Meijer, but I have found a link online for a pack of 4 of them: www.amazon.com/Sterilite-19344304-Gasket-Aquarium-Latches/dp/B00KL7VPWO/ref=sr_1_1?crid=3UGQWZAD2C4EY&keywords=Sterilite+19344304+54+Quart%2F51+Liter+Box%2C+Aquarium+Latches+and+Gasket&qid=1672073569&sprefix=sterilite+19344304+54+quart%2F51+liter+box%2C+aquarium+latches+and+gasket%2Caps%2C105&sr=8-1

[@AlexColeman-q1u]

Would it be more efficient (lighter and stronger) if you used a laser cutter to make the ends rather than gluing them??

[@balsaengineering6686]

I don't think using a laser cutter would be of benefit in that way. The glue joints are actually stronger than the wood itself. I would also be concerned about having the grain of the wood not be aligned like it is with conventionally cut strips. I don't have a laser cutter to play with though, so if you do, definitely give it a try and let me know how it goes!

[@lydiachi645]

Which type of wood would be better to use for SciOlympiad: Basswood or Balsa wood?

[@balsaengineering6686]

Hi Lydia, the best builds usually use both balsa and bass. Basswood is ideal for pure tension conditions like the bottom primary tension pieces here. For this build, everything was balsa, which can work fine, but it'd be better to use bass for the primary tension members. You might enjoy this video I made which talks about balsa density vs efficiency. I also compare it to basswood a bit at the end: kzbin.info/www/bejne/o6uwd5uaabikhpo

[@lydiachi645]

@@balsaengineering6686 Thank you!

[@謝昇達-k1v]

If the span of the bridge is changed to 600, can I scale it up?

[@balsaengineering6686]

Yes, I would say this design should scale up nicely especially if you can scale all the dimensions. If you are only scaling the span, it should still work, but might not be ideal

[@jqxz230]

Where do you recommend buying the bass wood? I'm having trouble finding the 1/16 x 1/32 wood.

[@balsaengineering6686]

This is my current favorite place for bass wood: fnabco.com/collections/basswood-sticks

[@sailshil]

@Balsa Engineering - What type of graphing paper do you use in the video? I've been struggling to find it.

[@balsaengineering6686]

Here is the link to the large 17x22 graph paper I've used. The 11x17 size is also useful for Div B. www.amazon.com/gp/product/B000HF6ZS4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

[@sailshil]

@@balsaengineering6686 - Did you use the 11 x 17 size in this video?

[@balsaengineering6686]

@@sailshil Yes, this is a Div B build and I used the 11x17 graph paper which is plenty big enough for full-scale

[@sailshil]

@@balsaengineering6686 Thank You!

[@drmikecubbin]

Big Fan (and SciOly coach)! I see you posted the STL files for the Div C jigs, but I don't see them for Div B. Am I missing them? The kids have made them as you outline in the video, but I think they could do even better if they printed jigs. To be honest, they have printed several variations of jigs, but maybe yours are a little more "exact" :) Thanks for all your guidance!

[@balsaengineering6686]

Hi Michael, thanks for the kind words! Enough people asked for the Div B jigs, I did post them awhile ago. The links are in the description of the 5900 Div B video: kzbin.info/www/bejne/gnqYn2eGf6uHeck Let me know if you have any trouble tracking them down

[@drmikecubbin]

@@balsaengineering6686 Many many thanks!

[@avishbangia2693]

Thanks for the video. Just curious, do you know the approximate density for the default balsa sheets or sticks on specialized balsa. I just want to see if that would be better than specifically adding light or medium

[@balsaengineering6686]

It really depends on what they have a lot of stock of at the moment. Sometimes I've ordered with no density specified and it's a compete range, and sometimes it's not. If you want light density, you should probably specify it and pay the extra. Good luck!

[@monk1s748]

where should I buy my balsa wood?

[@balsaengineering6686]

My favorite place is Specialized Balsa specializedbalsa.com/products/balsa_sheets.php but many places are fine to use

[@monk1s748]

tysm and is there any specific glue that is best?

[@unquiet3015]

CA glue

[@balsaengineering6686]

@@monk1s748 I like to use 50 cps CA glue

[@balsaengineering6686]

@@monk1s748 Check out this video on glue and gluing technique for more detail: kzbin.info/www/bejne/a2bPk2WBr7icrck

[@peterv1946]

Did you use type A, B, or C balsa?

[@balsaengineering6686]

For this particular build, it was just common A-grain. Usually I will just use A or B or whatever the general mix of those are as it's less expensive wood. For critical compression use cases when I'm doing some final optimization, I'll experiment with C-grain.

[@jerryzhang5024]

Great video! How did you exactly build your dynamic loading system when you are testing your bridge? Also, what wood did you make the loading block out of?

[@balsaengineering6686]

Thanks! The core components of my dynamic loading system were this load cell (which doesn't seem to be available anymore) www.amazon.com/gp/product/B07F922RZC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 and an Arduino UNO R3. I custom wrote the code to make everything work together. I've found after you calibrate it, it's pretty accurate, and even more important, it's very consistent, so it definitely works well for this use case. For the loading blocks... hmmm... I didn't make either of the ones I showed in this video. I think I acquired them over the years as extras from the testing rigs from the various schools I coached for. If you are going to make one, I'd recommend using a hard wood of some kind, oak or maple, etc. I think my grey one was made from laminated counter top material though, so just about anything can work. If not for competitions, you could probably 3D print them as well. Just use 100% infill to make it as sturdy as possible.

[@yashiisthebest8887]

what about the pass through block?

[@balsaengineering6686]

Hi! The rules are different this year, and there isn't a pass through block, which makes things much easier!

[@hi-ep4sg]

Would putting rice in the dry box be reasonable?

[@balsaengineering6686]

I would recommend using silica gel packs. I actually have a brand new video that should be out either tonight or tomorrow that is all about competition prep including the dry-box. Keep your eyes out for that for all the details

[@hi-ep4sg]

@@balsaengineering6686 got it, thanks!

[@psychosaggitarius]

did you laminate any pieces?

[@balsaengineering6686]

No, nothing special like that. Just simple surface to surface gluing for all the joints

[@psychosaggitarius]

@@balsaengineering6686alright, thank you! by any chance did you glue any of them together to form stronger sticks as one or did you just use one stick for each support? if using basswood

[@psychosaggitarius]

i have 3/32 inch basswood for reference

[@balsaengineering6686]

@@psychosaggitarius For this particular build, the "Getting Started" video, I used all balsa from a single sheet of 1/8" thick. I basically show the entire build in video. I don't do any lamination. For something like my 5900 bridge, and what I'd recommend, is to use a piece of basswood for the primary tension member. I like to use 1/16 x 1/32 for that piece as a great starting point.

[@balsaengineering6686]

@@psychosaggitarius Hmmm... are you asking if you can laminate those to create the legs? Maybe... but I definitely wouldn't recommend it, it will be too heavy. Try and find some light balsa and cut the pieces for that if possible

[@emankhalil8850]

Can you. please send me the measurements please

[@balsaengineering6686]

There is nothing like a template to share. The basic dimensions are determined by the rules. The free span (for Div B) is 35cm and the side height of this bridge is about 16cm when flat. I have the actual 3D jig STL files in the 5900 video description you can download to examine those in more detail if you'd like: kzbin.info/www/bejne/gnqYn2eGf6uHeck