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Thanks! Well, there is a difference between how much balsa the build actually needed versus how much was needed to be cut up to get just the right pieces. It's hard to put an accurate number on that ratio as sometimes you get more lucky than others, but it's probably anywhere from 3:1 to 5:1 or maybe more if you are really trying to get things perfect

Thank you so much for your kind words, they really mean a lot! If you're ever up this way, definitely reach out!

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

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

@@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: th-cam.com/video/SwmINqhpHL4/w-d-xo.html

There is no one right answer here as there is a trade-off on the size of the top. From a loading standpoint, you'd want it as large as possible as the angle would be steeper and there would be less induced torque in the legs. On the other hand, making it smaller allows for smaller cross members which get stronger in buckling proportional to the square of the length. I picked a size generally in the middle. Feel free to experiment with both options if you have the time and resources.

Good luck this season!

The links to the stl files are in the specific columns and bases videos where I show them in use

Hi! Some browsers block the download if you just click on them. Try copying and pasting the link into a new tab in your browser and then overriding the warning to download the file. If that doesn't work, send me an email and I can get them to you that way.

It’s much cheaper to buy sheets and cut your own. It’s also more flexible if you want non-standard sizes

I don't really have a template like that to share. Probably the best thing would be to watch my approach video that shows I designed the jigs. You can use that to try and create some kind of template. th-cam.com/video/JdWY8FcbSGI/w-d-xo.html I warn you though, it will be extremely difficult to make good tower without some kind of assembly jig. It doesn't have to be 3d printed, but you'll want to build something to help make it as symmetric and level as possible.

@@balsaengineering6686 Thank you! That video is really helpful.

I would not recommend that. Unless you make the base strong enough so it doesn't ever need those horizontal cross pieces. That is something worth experimenting with as you build devices this year. Good luck!

@@balsaengineering6686 Thanks! What about lower the cross pieces a bit so that they don't take weight during testing? I printed a loading block from a library but the library did not do a good job.

@@MsShuangshuang I'm not sure I quite understand what you are asking. The custom loading block should be a fairly easy thing for most printers to print. Try having them increase the infill to something like 40 or 50% and make sure it's being printed with the flat side down. That might help getting the block legs to print well.

​@@balsaengineering6686I will print it again. I was thinking instead of having the horizonal cross pieces right at the top, what about gluing them 0.5 cm down from the top. Will the base be as stable? I am working on nonbonus base and the cross sections will be slightly different anyways.

@@MsShuangshuang Having those top horizontal cross pieces 5mm down will probably be fine. It all depends on the rest of your build. Only one way to know for sure and that's to try it :)

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

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

@@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

Got it. Thanks.

The non bonus jig base I have provided is big enough to span the 20x20 square hole if you rotate it 45 degrees on the testing surface

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

@@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: th-cam.com/video/6jSlhXZORMs/w-d-xo.html

This information is contained in this video where I show my notebook pages. My benchmark column was build #12. If you check out at 13:17 you'll see my notes where it says I used 1/20 x 1/20 for the cross bracing. You can also see the exact mass for each layer if you want to calculate the density of material to try and match it exactly. Good luck this season!

Thanks so much for the speedy reply!

I always buy sheets and cut my own sticks. It's less expensive that way and you get more control over the entire process. A good place to start is 1/8" sheets for the legs. For the cross-members, there is no one correct answer. I have used 1/16, 1/20, and 1/32 thick balsa successfully. You can check out my notebook pages for these builds to see exactly what I used, size and mass if you want a good starting point. Good luck!

You can find the main jig files linked in the description of this video: th-cam.com/video/_QTOCIHE_1w/w-d-xo.html

without a JIG

@@YanaPandit-b2f I'm not sure how to do it without a jig either. That's why I created a jig to do the job :) In theory you might be able to create some kind of cutting device that sliced at at 60 deg angle and run the stick through twice, but that would most likely involve a custom 3d print as well.

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

Yes, the rules state that you are allowed to laminate wood together however you want. In general, it's better to just use larger or more dense wood though, as the glue involved in making a laminated piece usually makes it much heavier

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.

@@balsaengineering6686 Can you please tell which video excatly

@@YanaPandit-b2f This one tells about how I created the triangular legs: th-cam.com/video/MTHygxUS3YU/w-d-xo.html

⁠​⁠​⁠​⁠@@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?

@@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

I am excited to hear that it worked well for your class! Yes, the non-bonus build will be less risky this year just like last year. I have actually not built any non-bonus builds yet to know if it can be highly competitive. My gut says it can be, but that is something to explore. I decided to focus on the bonus for my video series as I knew that would create a very good result and be something to compare against. I really wanted to demonstrate the process, building/optimizing the pieces separately, and in that sense, the bonus and non-bonus are the same. Good luck this season!!

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

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

@@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

I would say a 3d printed jig is not required for great results, but some sort of assembly jig will be 100% required. You'll have to get creative and build something that will help you make it as symmetric and level as possible. In 2017, our team built an assembly jig out of a 4x4 block of wood, copper pipe, all glued to a wood base with a custom balsa top to hold the legs. It worked well, but it's much more work to create something like that.

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

@@balsaengineering6686 thanks!

I made an entire video on that exact thing :) You'll want to check out this video: th-cam.com/video/MTHygxUS3YU/w-d-xo.html

@@balsaengineering6686 OOOH thank you!!!

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.

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!

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

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

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

@@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.

@@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

Hi! I don't have any kind of paper template, but I would recommend you just use large graph paper and draw out your (or my) design to scale to get an understanding of what needs to be done. This isn't a 2d problem though, so we really need to think in 3d and use a 3d jig for assembly help. Good luck this season!

Please watch my video on the triangular legs to learn more about them: th-cam.com/video/MTHygxUS3YU/w-d-xo.html As for the cross-members, I had the most success using 1/16 x 1/16, but that is by no means the only option

Hi! That is a pretty odd request... I'm not sure why your teacher wouldn't print the version with a cone in it as it would be lighter and cheaper to print. I don't really have a solid version ready to go. Can you get someone else to print that top piece or perhaps outsource it on the web? Just that final piece shouldn't be too much. Sorry about that!

I have access to a copy of SolidWorks I've been using to create these jigs, although they aren't complex designs, so just about anything you're comfortable with should work fine.

The leg pieces are custom made refer to his previous video on triangular legs the dimensions are 3/16

As mentioned below, the legs are custom made. Check out this video for all the details: th-cam.com/video/MTHygxUS3YU/w-d-xo.html Good luck this season!

For the benchmark build, I used 1/16 x 1/16. I also built some with 1/20 x 1/20 with less success, but that doesn't mean it couldn't work. The video being published on 9/21 will show my notebook pages for all the builds where you can see exactly what I used and their masses.

@@balsaengineering6686 Awesome thanks!

I'm not sure I have a super clear picture of what you're proposing, but I'd say definitely go for it! This event is all about experimenting and that includes the jig design!

I just downloaded them both from the links above and verified that they are correct. The one labeled "_bottom" will have a hole on both sides and the one labeled "_top" will have a hole in the bottom with a flat surface on the top. Please try downloading them again

@@balsaengineering6686 Thanks for sharing! For the two STL files producing a Division B column jig, I found both the bottom and top parts are 13 cm tall. Because the 2025 rule requires 50cm height for the tower, I wonder if you suggest any scaling number when printing them?

@@rosecarmen453 The two STL files in this video are for ONLY the column part of the build. You also need to build a base and ideally print a 3d jig for that as well. Please watch this video to learn about the base: th-cam.com/video/juhgy5LAAgI/w-d-xo.html You will also want to watch the final assembly video to learn how to attach them together. Please watch all my 2025 Div B videos in full to better understand all the rules and what you'll need to do this season. Good luck!!

Still the same risk. My initial thinking is the bonus would be better because they have the same column dimensions, but I have not even tried to build a non-bonus version yet. It's something that needs to be explored for sure. If the non-bonus can come close to my benchmark bonus score, then it'd definitely be a better choice as it wouldn't be as risky on competition day. (Div C is a different story, I'm more confident that the bonus is the correct way to go there due to the 3-leg design and how it needs to still span the 20cm square in 3 different quadrants)

I haven't given any real thought to a good non-bonus design. The best non-bonus design might be some crazy non-symmetric tower. I'm pretty sure the best choice, at least to start with, is the bonus. But feel free to see if you can come up with a non-bonus version that can beat the benchmark score! That's basically the whole point of publishing the benchmark results. If you can create a non-bonus version that can beat it, or come very close, use that. Otherwise it's best to stick with the bonus.

Hi! I like to buy my balsa sheets from Specialized Balsa because you can specify the density range when ordering. specializedbalsa.com/products/balsa_sheets.php The final video of this series, due to be published on 9/21, will show my notebook pages for all my builds including the benchmark one. From those notes you'll be able to see exactly what I used for everything. As I mentioned in this video, these legs were made from 3/16" square source sticks. Good luck this season!

@@balsaengineering6686thank you!

Interesting! I had never heard of pre-cut 60/60/60 sticks, but it's good to know Hobby Lobby at least has something. I would recommend making them yourself from sheet balsa because you'll have way more control of the density and most likely, it will also be much cheaper. Good luck!!

Hi! The dimensions of the cutouts in the jig don't matter too much, they are only to help the cross-members not get glued to the jig. The critical dimensions for this jig are the outer dimensions because the legs actually go on the outside of jig. It needs to span the 29cm circle with only 3 legs, so that part is almost a minimum sized jig already, but feel free to re-design it in another way if you want. My jig and designs are only meant to be a starting point for you this season. Good luck!!

Yep! I have 2 more videos coming in this series. On 9/17, I'll publish the one where I talk about the assembly challenges, and then the one you are specifically looking for will be published on 9/21 where I show my optimization path to achieve the benchmark tower. That one will show all my notebook pages which includes everything you need. Good luck this season!!

Yeah, regular sand is very dusty. I found that using sand-blasting material works pretty well. Make sure you get the medium grit. It doesn't generate zero dust, but it's way less than typical sand: www.amazon.com/gp/product/B0791W9MXL/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I mentioned in the video 3/16" square legs as the source: th-cam.com/video/MTHygxUS3YU/w-d-xo.htmlsi=k2m2p4nMrgML72bl&t=115 The length just needs to be just a bit longer than the final length. I was using 52.5cm.

I mentioned in the video that I started with 3/16" square sticks: th-cam.com/video/MTHygxUS3YU/w-d-xo.htmlsi=k2m2p4nMrgML72bl&t=115

That's a very nice approach too. If that works well, it would definitely be less messy than sanding it!

u gotta hit copy link address and then past it into ur browser, its flagged a suspicious download so that's why it wont open

@@hipeoples9607 Yep, thanks for clarifying. I'm not sure I can do anything about the browser flagging it.

@RichardTapp1 I haven't read that book specifically, but I did basically confirm the same findings experimentally. You might enjoy this video if you haven't seen it already: th-cam.com/video/mzMFhd4SqP8/w-d-xo.html While the higher density balsa has a higher absolute efficiency, there are diminishing returns and because we are limited to 15kg max load, we are generally in the light to light-medium range for anything that has buckling. The exception is when we know pieces are in guaranteed pure tension (nothing in the tower), then you want to use either high density balsa, or that's when it's even better to use basswood. If we could build devices to 25+kg max load, I think we'd see higher absolute efficiency numbers, but for our condition, it just makes it too overdesigned and too heavy.

The best option is to find a printer that can print it in one piece, but if that is not an option, I have had success with Microsoft's free tool 3D Builder to cut up STL files.