I noticed you've been using bonus tower designs for the past videos, does this mean that a bonus design would be worth it with this year's rules? Or is it still the same risk?
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 Balsa Engineering! I just wanna know where do you get your balsa wood from? Like is there an online store that you could possibly send a link too? Also, what are all the measurements for the wood that will be used in the build? Thanks!
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!
I just went to hobby lobby to look for a new ruler and happened to stubble upon some precut equilateral triangular beams. but the density and variations of density is absolutely crazyyyy
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 Balsa Engineering! I'm curious as to why the 3D print is that big on the x&y dimensions where the cutout is. Was there a certain reason for that? Would it be fine if I made a jig that was much smaller but had the same cutouts? Thanks.
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!!
Hi, balsa engineering! I watched the all division c 2025 videos so far, and are you going to make a video that shows each mass of all balsa woods? Like density of 2 layers of crossmembers at the bottom, and weight for each legs. Thanks for your video!
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: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-MTHygxUS3YU.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: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-MTHygxUS3YU.htmlsi=k2m2p4nMrgML72bl&t=115
Very interesting approach. I opted to create an angled stripper where you feed the member through a hole with a blade angled down at 60 degrees to cut the excess wood off. Once you run the member through the stripper twice, you are left with an equilateral member.
Have you read "Variables affecting the strength of balsa wood" by P D Soden and R D McLeish University of Manchester 1976? I dont have my copy handy but from memory, heavier balsa has a better strength to weight ratio than lighter balsa. So you may be better off with smaller cross sections of heavy balsa. Whether this effect is enough to offset worse Euler buckling outcomes, I am sure you could calculate. As well as matching balsa lengths by weight, you could also select for superior stiffness by observing deflection of same weight samples as cantilever beams under light load. This might also help expose samples with weak portions.
@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: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-mzMFhd4SqP8.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.
How would you recommend 3d printing the jig if my printer isn't big enough? Should I just use software to cut it in half and then print it? Or would that cause inaccuracy?
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.
Hey, thanks for the great video. I get my wood from Hobby Lobby, and sometimes Balsa is hard to find and not the best quality. However, I have seen Basswood. Me and my partner want to test the differences out. Do you think it is worth considering basswood?
Definitely give basswood a try if you want, but you'll probably find that it's way too heavy to be competitive. It is generally only the best option for pure tension conditions. FWIW, I like to buy my balsa in sheets from Specialized Balsa and cut my own sticks and that has worked well. Good luck this season!
Would you still use 1/24 by 1/24 for the cross members? I asked this last year lol also, what density should I buy? I calculated around 5-6 pounds per cubic foot, but I'm not sure
There is no one right answer for the cross-members. Using 1/20 is a good choice, as is 1/16 for the base at least. For the column, you might want to look into using 1/32, but it all depends on the density. You'll have to experiment with that a bit. In the final videos of this series, I'll show what exact material I used for the benchmark tower. Stay tuned!
I will provide links to the STL files I used for the jig and other support objects in the upcoming videos where I show how to use them. The column video will be next (9/14), and the base one will be early next week (9/17). Thanks!
Some other people have mentioned that browsers can tag the downloads as insecure and block them. It seems the way around that is to right-click on the link and paste it into a new blank browser tab and tell it explicitly to download it. These files download almost instantly because they are so small, so also check your downloads folder to see if it did download properly and you didn't notice it
For all of these builds, I did not worry about the balsa grain. In general, it's way more important to get the density/mass correct and matching than it is to worry about the grain type. I'm pretty sure the benchmark build used generic A/A-B grain for everything. I wouldn't focus on using c-grain for anything until you have nailed down optimizing everything else as it's much more expensive to work with and really won't help a whole lot in these builds.
For my dry boxes, I just use super-cheap ones from Amazon that do the trick. It's not important that they are incredibly accurate, just to know that your box is working properly compared to ambient humidity: www.amazon.com/Thermometer-Hygrometer-Temperature-Fahrenheit-DWEPTU/dp/B08M3P74N3/
Is it just me or are the STL files not working? Does it automatically download as soon as I press it or am I supposed to be directed to another website?
No, there is no modifying the jig after it's printed. There are also no grooves for the legs this year as they aren't square. Stay tuned for the next video to learn about how I go about creating the legs we'll use for this build.
@@Guthhhiii Correct! The next video released will show how I use 3/16 x 3/16 square source sticks to make the 60/60/60 triangular ones that will work on this jig (with tape)
I think the best solution to achieving equilateral triangular members is simply to custom order them from balsa manufacturers. This is the route I will be exploring.
You will want to wait and see my next video. If you have access to a 3d printer, I will show you how to make perfect 60/60/60 legs from square source sticks in < 5 min (and possibly < 2 min)
@@emilyclarke7842 My next video will be out on Saturday morning (9/14), then Tues 9/17, then the following Saturday 9/21. Good luck this season! Thanks!!
Is there a advantage/disadvantage to using a modified square vertical member (with two sides sanded to 60 degrees) as opposed to equilateral triangles?
I might not be understanding your question properly, if you sand 2 angles to 60 degrees, doesn't that make the 3rd angle also 60 degrees and thus an equilateral triangle? In general, we want these leg cross-sections to be as symmetric as possible to resist buckling equally in multiple directions. My entire next Div C video is all about creating these triangular legs. I found a solution that made it fairly easy to accomplish. Stay tuned!
@@timchristensen5548 Ahh, something like that might work to some degree, but wouldn't that still give you issues with perfectly flat sides on all 3 faces? Unless you mean not making an equilateral triangle tower. There are definitely different shaped towers that could work, and perhaps some non-symmetric ones could do very well, but I choose to just focus on the simplest option for now. As soon as your tower isn't symmetric, you'll have to optimize legs and cross members on a per-side basis. Not impossible, but definitely more work. Thanks!!
@@balsaengineering6686 thanks for your patience! yes it would still be a overall tower that is a equilateral triangle. Each of the verticals would be a 60-105-90-105 quadrilateral. Doing this would allow the jig (if each vertical groove had a 90 degree surface) to act as a sanding guide to create the 60 and 105 angles.
@@timchristensen5548 Hmmm, maybe. Definitely something to try! I don't like the idea of sanding the legs on the assembly jig though. I think I came up with a better solution :) Stay tuned for the next video!
Stay tuned! I plan on releasing all the STL files I used for this build including the jig and other supporting pieces. I want to wait until I have videos out explaining how to use everything as there are some unique challenges this year. My plan is to have all the initial videos published by 9/21
I’m just popping in to say thank you for these videos, im from a school that has never done great in build events in general and that doesn’t have great supplies such as balsa wood. I used all of your videos to help me last year and while I had some issues with getting wood I ended up getting a 2nd place medal at our regionals.
Thanks for your kind feedback! Stories like yours are exactly why I make these videos in the first place! I am really happy they've been able to help you out. Good luck this season if you are competing again!
I like to buy my balsa sheets from Specialized Balsa. Future videos (within the next 2 weeks) will provide more details on exactly what I used this year to achieve my benchmark build.
Stay tuned! I plan on sharing the links to all the STL files I used to create the benchmark tower. I want to wait until I show them in use before sharing as there are some unique things to using them this year. I plan on having all these first round of videos published by 9/21. Thanks!
Hi! Yes, I plan on releasing all the STL files I used for making the benchmark tower. There are quite a few new challenges involved this year, so I'm going to wait to release them until I have the videos out where I show them in use. I plan to have everything published by 9/21, so stay tuned! Thanks!!
You can get good wood from a lot of different places but I like to use Specialized Balsa because it is one of the only ways to get exactly the density range you want.
@@steamedfrog8386 I will include all the details of my benchmark build, but not in that specific video. I will show all the details in some of the videos after that one where I talk about how I went about optimizing the tower. I hope to have them all out by 9/21, so you shouldn't have to wait too long. Thanks!
Hello Balsa Engineering, after looking through the division c tower rules, it has come to my attention that nothing has changed from the 2024 division c rules from last year. Please do correct me if I am wrong, that would be much appreciated 😃! If I am correct, would this mean we can use the same videos that you made last year? Thanks you!
Hi! The rules for both divisions this year are very different from the rules in 2024, so definitely don't reference my build videos from last year. Very soon, my next two videos will explain the rules for both divisions and explain the differences, so keep an eye out for those!
Thanks so much for the videos. Do you have a separate jig for cutting the Div C long members into equilateral triangle cross section? I designed and printed one and the members seem to come out pretty close to an equilateral triangle.
Dude uploaded like 3 seconds after specs came out. Mad respect. I owe you a ton - I got 1st at the U of M invite as a freshman last year for towers. Thank you for all that you do for us.
Congrats and thanks for the kind words!! I have been working for 2+ months with the draft rules, so I was glad when nothing changed! I have all my initial videos ready to go, I just want to release them over the next 2-3 weeks so people don't get overwhelmed and have time to watch them in order. Stay tuned... 12 more videos are ready to go!
Thank you so much! I followed and learned a lot from you last year. Is there a timeline for which your planning to publish certain videos or is everything quite fluid.
@@MichaelIsaac-kd1ki No worries, either way is fine. Some people want to ask specific questions about their design or build and don't want it public. My current plan is to have all the videos released by 9/21. I don't want to release them all at once so people have a chance to digest them and ideally, watch them in order.
