2025 Science Olympiad Tower Div C: Optimization

[@asteralemayehu4973]

Hi Balsa Engineering, first off I wanted to thank you for making these videos! I found them really helpful last season and I was able to get second place at states thanks to you! For this seasons build I was wondering which type of balsa sheets (dimension's and density) you used for you benckmark build. Thanks!

[@balsaengineering6686]

Thanks for the kind feedback and congratulations on your success last season! If you check out 7:45 of this video, you can see my notebook page for the benchmark build. There I show the sizes and masses of everything I used from which you can calculate the density. To save some time, I believe the source legs (3/16 square) were about 11 lbs/ft^3 which is in the "medium" range. The cross members were all 1/16 square. I didn't calculate the density, but I'm sure they were in the "light" density range. You can see the mass of the entire layer on the far right side of my notebook page in red. For example, the bottom layer had (6) pieces that were 25.5cm each and the total mass was 0.488g. Good luck this season!

[@AmeyMishra22]

Hello! I see that the jig included in the shared folder is the Bonus one. Are there any plans to share the non-bonus version? Thanks in advance!

[@AmeyMishra22]

Nevermind, just saw the approach video! Idk how i missed that lol.

[@arjavjain3279]

Hey balsa engineering thank you so much for making videos like this. But I had a confusion on what the size of the base is for for the jig.

[@balsaengineering6686]

Thanks! My overall approach video shows all the details of the jig design and dimensions. Let me know if you still have questions after watching this: kzbin.info/www/bejne/lYK3gHZ_faqSZ9k

[@arjavjain3279]

@@balsaengineering6686 Thank you so much for the help much appreciated. I think I just missed this video when watching this series thank you so much for highly informative videos every year for such build events.

[@ykspecs1833]

Hi balsa engineering. I was wondering where I can buy the balsa sheets? Also, How did you cut them? Thank you.

[@balsaengineering6686]

I like to buy my balsa sheets from Specialized Balsa: specializedbalsa.com/products/balsa_sheets.php To learn how to cut them, please watch this video: kzbin.info/www/bejne/mH3WhYKmotStfas Good luck this season!

[@torreyblack76]

How long did your 3d printing take. My printer is small and had to slice everything for the tower in half and building the jig by pieces. Thank you for all you do for these kids. Very methodical process you have that these kids need to learn it.

[@balsaengineering6686]

Thanks for the kind feedback! I don't recall the exact print timing right now, but they take a long time. On the order of 10-20 hours per piece

[@alexf9480]

Hi Balsa Engineering! My 3D printer has a base of 220 mm, and it is not big enough to print the bottom layer of the Div C bonus jig (260 mm across). How much impact on the construction of the tower would it be to split the bottom trapezoid and print the two halves separately? (cutting through the middle of the triangle parallel to one of the sides)

[@balsaengineering6686]

That should be OK. Just tape the two pieces together as tightly as possible and it should work fine. Good luck this season!

[@justsophia3329]

Hello! What are the units for the lengths of the legs and cross members?

[@balsaengineering6686]

Those measurements are all in cm

[@JackChen-l7f]

Hi Balsa Engineering the program im using doesnt support zip files so do you have the same jigs but as a stl file(divison B)

[@balsaengineering6686]

Hi! Just use Windows (or MacOS) to unzip the file first. All the stl files are included in that single zip package

[@completeandabsolutenerd]

Based on my calculations, your source wood at a length of 36 inches had to be around 3-3.5 grams, right?

[@balsaengineering6686]

That sounds about right. Probably closer to 3.5g, although I didn’t keep track of that. I did record all the 52.5cm source legs though and they ranged from about 1.9 to 2.2. Only the final sanded weight matters though, so that is the library of material you want to build up to choose from

[@completeandabsolutenerd]

@@balsaengineering6686 Thank you. I've been at it for the past hour, trying to find the right weight wood. Been getting wood too light, but never too dense, but just finally struck a 3.3. Hopefully I can get more!

[@potatoooeed7581]

Hi Balsa Engineering! Thank you for making this video for this season. I was working on making the most optimized or the benchmark tower for this year. The mass for the tower I made ended up being around 1.2 g heavier than yours. Do you know what could lead to this issue? I’m thinking it could be the amount of glue I used or something like that. Thank you!

[@balsaengineering6686]

If you check out the video at the 6:56 mark, you can compare your build to my benchmark tower in great detail. I show the mass of all the parts including the legs and the combined mass of each layer. My guess is you are using slightly heavier balsa than I used, but you can compare your build exactly if you recorded the weights for your tower pieces (which I highly recommend).

[@potatoooeed7581]

@@balsaengineering6686I’m confused as to how I made this mistake, but I made 11 crosses instead of 10?? According to the notebook page, it should be 4.6 cm from the bottom to top of each cross. The length of the stick is 52.5 cm, so how did you cover for the rest? I think I’m tripping on the math while building it 😭

[@balsaengineering6686]

@@potatoooeed7581if you re-check my notes, the first layer of cross members starts at 0.5cm from the bottom and then the spacing is 5.1cm between layers. Btw, having 11 layers is not a problem and might even be better depending on your materials

[@potatoooeed7581]

⁠@@balsaengineering6686thank you so much! I had another question about reducing the weight, as of now it’s still heavier by about 0.9 or so even after reducing the number of crosses. Why would 11 crosses be better? Also, if my balsa is just heavier, could I just remove one of the cross members on one of the top crosses? Thank you 🙏

[@potatoooeed7581]

I think I found a part of the reason, the design I built is almost exactly like tower number 1 rather than 5. My leg masses are similar to the first one. How did you reduce the mass of the legs? Is just just by sanding it more

[@demonplayz857]

Hello balsa engineering, I noticed that this year you didn’t list the densities for the wood to the left of the tower. You did last year,is there any way you can provide me with those numbers?

[@demonplayz857]

Preferably for the 36in and 48in sticks, thanks!

[@balsaengineering6686]

@@demonplayz857 I have the mass listed for the entire layer of cross members, so some simple math will get you source stick mass. For example (6) @ 25.5cm at 0.491g is 153cm or 60.236 in. For a 36" stick, that is just 36/60.236 or 0.598*0.491g, so 0.294g for a 36" for that layer. You can then compute the actual density if you want by knowing the volume, just make sure you get your units correct.

[@demonplayz857]

@@balsaengineering6686for the legs are they actually 52.5 cm long or will it be 51.5cm long? I know you say the little space between the first layer and the ground is around 0.5 m, and from there each section is 5.1 cm long, doing the math it would be 51.5 cm? But on the 5th design you said it was 52.5 cm long?

[@김지윤-f5b3e]

Hi, balsa engineering! Thank you for the video. Can I just order triangular leg, not sanding the square leg? Because it can make some errors or mistakes.

[@balsaengineering6686]

Hi! I don't know of any place where you can buy 60/60/60 legs. If you find somewhere, please let me know!

[@completeandabsolutenerd]

I checked with National Balsa and they do not unfortunately produce such legs.

[@balsaengineering6686]

@@completeandabsolutenerd Yeah. Specialized Balsa sells pre-cut 45/45/90 legs, but that's not ideal for our use case either

[@completeandabsolutenerd]

@@balsaengineering6686 I hope we can find a vendor who will do that because that will save a lot of time and effort, as well as wood waste.

[@balsaengineering6686]

@@completeandabsolutenerd It's not too hard to make them. I found it was about 2-5 min per leg depending on your technique. It will definitely be much cheaper to make them yourself as well

[@niranjankothandaraman]

Hey Balsa Engineering, I am competing in tower for the first time and would like to play with this design. Where can we find the lengths for tower 5 as this was the most optimized one. The lengths of the cross structures and the legs would be helpful. I was also wondering where you got the specific balsa wood sticks. I would like to get the same ones so that I can minimize any flaws.

[@balsaengineering6686]

Hi! You can find the detailed information on each of these tower builds right in this video. For #5, check out my notebook page at the 7:44 mark. Everything in blue on the right shows the lengths of the pieces in cm. The red is is total mass for each grouping. You can compute the exact density by know the size which is also shown (1/16 square for the cross members). I like to buy all my balsa in sheets from a place called Specialized Balsa. It's not that the wood is better, but it's the only place I know of where you can specify the density range when ordering. I would highly recommend you check out some of my general videos to learn more about getting great material to use. Here is one to get started: kzbin.info/www/bejne/mH3WhYKmotStfas

[@niranjankothandaraman]

@@balsaengineering6686 Thanks, I'll take that into account. Our club itself has some Balsa wood sticks, I'll see if it matches the density of it. If not I may need to order myself from Specialized Balsa, do you know the rough estimate of delivery time?

[@niranjankothandaraman]

I also just want to make sure, the height of each leg is 52.5 cm, the increment for where each cross member needs to go is 4.6 cm. And the length of the cross members itself starts from 25.5 cm and goes till 7.4 cm., dimensions of each balsa stcik is 1/16 x 1/16 inch. the top has 3 (4.5 cm ) sticks.

[@balsaengineering6686]

@@niranjankothandaraman They are a small family-run business, so their delivery speed changes a lot depending on how busy they get. My experience has typically been about 1-2 weeks or so.

[@balsaengineering6686]

@@niranjankothandaraman That is mostly correct. The cross-member layer spacing is 5.1cm (the first one starts at 0.5cm from the bottom). Also, don't forget about the bottom 3 horizontal pieces that are 26.0cm each.

[@TINAMARTIN-t1h]

Hi, I am trying to use the link that you inserted in the caption to get info on the jig, however when i click on the link and try to download the files its saying no file to preview and i am unable to get anything off that link. Do you have any idea why this is happening or how i could get the date of the link?

[@balsaengineering6686]

I just tried it and it's still working. It should auto-download a zip file which contains all the stl files. Once you click on it, go to your downloads directory and see if you have it

[@DhruvPatel-eo7di]

Do you recommend your three legged tower or is a four legged tower good? For division c

[@balsaengineering6686]

Please read the rules carefully. This year, it needs to be a 3-leg tower for Div C.

[@DhruvPatel-eo7di]

Thank you very much I think I never read that part

[@cloudovervalley]

Hi, Balsa Engineering. How long does it take to build a tower? I haven’t signed up for the event yet. I’d like to know the time commitment for this event vs other events. Thank you.

[@balsaengineering6686]

Hi! I would say it takes about 2 to 4 hrs to build a tower once you have the material all ready to go. It can take hours to prep the material depending on how much effort you want to put into it

[@cloudovervalley]

Thanks for responding. Do you know the estimated hours for the whole process?

[@balsaengineering6686]

@@cloudovervalley It really depends on how competitive you want to be. You can get by with 10s of hours. The top National teams will put in 100s of hours over the course of a season

[@cloudovervalley]

Got it. Thanks.

[@SophiaY-c7z]

Hi Balsa Engineering! Should I use light-density balsa or medium-density balsa for the main legs?

[@balsaengineering6686]

Hi! I think if you do the math to calculate the density of the source sticks I used for the legs, they are around 11 lbs/ft^3 which put it more in the "medium" density range

[@steamedfrog8386]

@@balsaengineering6686 Hey balsa engineering this might be a weird question but im trying to build 5 towers, and im buying balsa sticks that are 36 inches long, how many sticks would I need to make 5 towers (for cross members only). Im thinking of buying 50 sticks but i dont know if thats enough or too much :(

[@balsaengineering6686]

@@steamedfrog8386 Math is your friend :) If you check out at the 9:06 point in this video and see my notes, I show the lengths of all the cross members and horiz members. It adds up to 1055.1 cm which is 415.4 in which if you had perfect utilization would be 11.54 sticks at 36" each. That is not possible though, so add a couple sticks extra for each build. 13-15 for each tower is probably a good estimate. BTW, I recommend buying sheets of balsa and cutting your own sticks, it's much cheaper that way. Good luck!!

[@sillyegbert-mn2zd]

How do you calculate the 11lbs for the legs?

[@balsaengineering6686]

@@sillyegbert-mn2zd From the notes in my video, we know the source sticks were 3/16" x 3/16" x 52.5cm. First we can calculate the volume of that in cubic feet. Converting to inches, it's 0.1875 x 0.1875 x 20.669" = 0.7267 cu in. Divide by (12*12*12) to get to 0.000421 cubic ft. Next we know the source stick mass is roughly 2.1g from the video notes. Convert that to lbs and you get 0.00463 lbs. Our final answer is then just 0.0046297/0.00042052 = 11.01 lbs/ft^3. Hope that helps!!

[@NabilAksamawati-Arja]

Hello balsa engineering, Should I get light or medium weight for the legs and cross members? Thanks!

[@balsaengineering6686]

Well, you should experiment a bit with that. I would start with light for the cross members and probably medium for the source leg material. If you check out my notebook pages in this video, you can calculate exactly the density I used if you want to try and duplicate it as a starting point

[@NabilAksamawati-Arja]

@@balsaengineering6686 thanks!

[@nooby8828]

hey balsa engineering, should I order 1/16 * 1/16 inch and 3/16 * 3/16 inch cross members and legs?, also could you tell me what the numbers at the right of your notebook drafts mean?

[@nooby8828]

Also, you didn't make the cross bracing triangular, did you???

[@balsaengineering6686]

@@nooby8828 No, the cross members are normal square pieces. The blue numbers are the cross members lengths and the (6) means 6 pieces at that length. The red value on the far right is the total mass of the entire layer. If you get a chance, watch this video I made on how I take notes. It's from last season, but I'm doing the same things for this year as well: kzbin.info/www/bejne/bJu2nZuOj7SFg9U

[@madisonwhite7811]

What glue do you recommend for a strong tower?

[@balsaengineering6686]

The short answer is 50cps CA glue. The long answer is to watch my 25 minute video I made on this exact topic: kzbin.info/www/bejne/a2bPk2WBr7icrck Good luck!!

[@madisonwhite7811]

@@balsaengineering6686 Thank you! Do you prefer thick, medium, or thin 50cps CA glue.

[@balsaengineering6686]

@@madisonwhite7811 50cps is what defines the viscosity. 50 is somewhere between the typical "thin" and "medium" ratings

[@ivyyyyao5680]

Hi, where can i find the stl files that you used for the main three-legged jig? Thank you!

[@balsaengineering6686]

You can find the main jig files linked in the description of this video: kzbin.info/www/bejne/lYK3gHZ_faqSZ9k

[@butterflyindisguise3838]

Does 26cm base for the equilateral triangle tower actually fits outside the 29cm circle? I have been trying to do the math and 26 cm side lengths keeps giving me the perpendicular bisector of 22cm instead of 29cm. Idk if I did the math wrong but it would be great if u could show me how u did it

[@balsaengineering6686]

I looked it up :) I can't remember exactly which source I used originally, but here is one that shows the length of a side for our case: socratic.org/questions/what-is-the-area-of-an-equilateral-triangle-inscribed-in-a-circle The formula turns out to be sqrt(3)*r or 25.11cm. You can always just draw it on graph paper and measure, that is a good way to verify it as well

[@butterflyindisguise3838]

also how do figure out how to space your trusses out and how many of them you want?

[@balsaengineering6686]

@@butterflyindisguise3838 The ideal cross bracing spacing is closely tied to the strength of the legs you are using. You basically have to optimize them together and it's going to involve some trial and error. I recommend you check out my 5-part series on tower basics to see exactly what I'm talking about, specifically you'll want to watch this one carefully: kzbin.info/www/bejne/iajQeoGnndV7gpY

[@MichaelIsaac-kd1ki]

Hello, is there a reason why you added a horizontal bracing to the top and bottom of the tower?

[@trintoon]

not 100% sure on the reason for the bottom but the bracing on the top helps with dispercing the weight since the it gives more surface area for the loading block to lay on.

[@balsaengineering6686]

Actually, the block doesn't sit on the horizontal pieces at the top, so that's not the reason. Because the base is much wider with this bonus design, the bottom is pretty much in pure tension, for which a horizontal piece can help a lot. The top piece, I just decided to go a little conservative to make sure the legs didn't fold in on themselves. I would recommend you experiment with removing both for your builds and see how it goes! They may or may not be necessary depending on your cross bracing! Good luck this season!

[@YanaPandit-b2f]

So, I got Balsa Wood of 1/8" × 1/8" and 1/16" × 1/16' and 1/4 ×1/4" can I make a tower from this measurements

[@balsaengineering6686]

Sure. You'll just need to make your own sanding jig to make triangular legs out of 1/4 x 1/4 sticks instead of the 3/16 square sticks I used

[@rjassociates4028]

hey, so i had a question the legs, I got the square ones is it okay or i have to cut the quarter to triangles

[@balsaengineering6686]

You can try and make a tower with square legs, but you won't be able to get flat surfaces to glue your cross members to. Some of my other videos in this series show exactly why that is the case and how you could make 60/60/60 legs.

[@YanaPandit-b2f]

@@balsaengineering6686 Can you please tell which video excatly

[@balsaengineering6686]

@@YanaPandit-b2f This one tells about how I created the triangular legs: kzbin.info/www/bejne/g4Wrqpquirhmj7c

[@butterflyindisguise3838]

⁠​⁠​⁠​⁠@@balsaengineering6686does it have to be a 60/60/60 triangle? Can it be any shape as long as u can cut it so it can have enough surface to place the crossmembers?

[@balsaengineering6686]

@@butterflyindisguise3838 If you want a 60/60/60 tower like I have shown here, the legs will need to also be 60/60/60 to have perfectly flat surfaces on all sides

[@lemonboi-c4x]

So what’s the height it’s supposed to be?

[@balsaengineering6686]

The rules state that the height of the loading block must be at least 50cm from the testing surface. My builds have the height at 50.5cm to provide a little buffer

[@lemonboi-c4x]

What glue u use?

[@balsaengineering6686]

The short answer is 50cps CA. For the long version, please check out this video: kzbin.info/www/bejne/a2bPk2WBr7icrck

[@sillyegbert-mn2zd]

Are you starting with 36 inch long legs?

[@balsaengineering6686]

I started with 36" sheet balsa, then I cut the source legs to a normalized 52.5cm (you can see this in my notebook images) to create the 60/60/60 legs. The final exact length is achieved by sanding the top off while it's in the assembly jig

[@sillyegbert-mn2zd]

Thanks. So are the weights listed the 36” or the 52.5cm?

[@balsaengineering6686]

@@sillyegbert-mn2zd 52.5cm You can always get this information from my notebook page shown. Check out the 6:58 point of this video. I have written for the legs (source) 3/16 x 3/16 x 52.5cm