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You need to make sure your tower follows the rules. The ring needs to fit around the finished tower at a height of 25cm above of the testing surface.

I like to buy my balsa sheets from Specialized Balsa: specializedbalsa.com/products/balsa_sheets.php

I've still been using the container I used for the 60cm towers from last year: www.amazon.com/gp/product/B0BKD1VMMB/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1 It's a bit big for 50cm towers. I would recommend you try and find something smaller. Just make sure it has the foam insert on the lid and it should work well.

Thanks! Yes, if I recall, the source legs were in the "medium" density range at around 11 lbs/ft^3. I don't have the value for the cross members off hand, but you should be able to compute it exactly from the masses I've shown in my notebook page. They are definitely in the "light" range.

@@balsaengineering6686 Thank you so much for taking time to respond to our question.

Hi! At the 3:17 point in this video I actually show exactly how I cut my strips using 1/16" x 1/16" as an example. Have you tried this and it doesn't work for you? You definitely need to get a balsa stripping tool like I show in the video, but that is much cheaper than buying individual sticks. Good luck!

I'm not sure what the exact minimum size at the top would be. My design here has a pretty small top, I wouldn't want to go too much smaller. Remember, you have to thread the eyebolt and chain through during testing and you don't want to risk breaking it.

No, I don't sell anything. You can download my STL files for free linked in the description and print them yourself (or pay a service to print them for you if you want)

Please watch my videos on the bases and columns (and the latest non-bonus tower). There I show my notebook pages which show exactly the sizes and weights of all the pieces. In general though, 1/8 x 1/8 for the legs, and "smaller" for the cross-bracing.

@@balsaengineering6686okay thank you so much, after 3 attempts my tower still weighs 12 grams

@@Waddle_Soloz You just have to try and track down lighter source wood if you want to cut that in half. You can order that from Specialized Balsa or if you shop locally, pick out the lighter sheets and go from there

Currently I have no plans for that. I really don't think it's the right approach given the rules this year, but definitely reach out to me if you try it and find something that works well!

Ok!

For airplane building, small differences in density probably don't matter too much. This video is mostly about the Science Olympiad structural event where we worry about every 0.1g so getting the exact perfect mass/density for each piece is critical

You can see that when I show my notebook pages, for example at 3:45. Most of the cross members for this build was 1/16 x 1/16. Many options can work for cross bracing though depending on the material you have on hand.

Thanks!! I found that the best way to attach the pieces of the jig together are to just use masking tape on the outside. No glue or adhesive is needed. By using tape, it ensures the flattest possible connection and the tape is plenty strong enough.

@@balsaengineering6686 Thank you so much for your prompt response. I cannot thank you enough for making these videos and for responding to every single question asked.

That is a rule for Div C. Div B can be a conventional 4-leg tower.

They are in mm. You will need to scale them to something like shown at 2:58 to get a full-sized jig for a complete leg

If you send me your email (just email me), I can email you the zip file that way

I never even bothered make a non-bonus design for Div C. I really don't think it's the right approach this year given the rules. I encourage you to try and make one if you want and experiment, but I think the bonus is the way to go.

@@balsaengineering6686 appreciate the response and makes sense. Thank you!

Thanks! The answer is "light enough" :) Most of these pieces are in the light density range, especially the legs of the column. The best way to judge if you are in the right ballpark for density is to just check my notebook pages and compare to the masses I show for every component. You can compute the exact density if you want, but it's easier to just use the mass. Good luck!

Hi! Yeah, this step sands away more than half of the original stick. You can double check my math with the info in my notes, but I think my original source sticks were around 11 lbs/ft^3 for density which puts them in the typical "medium" range. Usually the medium range balsa is the easiest to get, so hopefully you can track down some heavier wood for this application. Good luck!

You shouldn't have to scale anything for the Division B files. The only file that needs scaling (and replicating) for Div C is the triangular leg sanding jig.

I believe the design log multiplier was removed for this year, but double check the latest official rules to be sure

You can see that in this video when I show my notebook pages. For example, at 6:58 The bottom horizontal layer is at 0.5cm and each layer after that the spacing is 5.1cm.

By this I meant the horizontal member above ot

@@King_Kay_66 You can see that information (and more) in this video when I show my notebook pages. For example at 5:17 On the drawing on the right side, the first layer is at 0.5cm and then each layer has a spacing of 5.2cm

Hi! The short answer is I like to use 50 cps CA glue. The long answer, including techniques, is the dedicated video I made on that topic: th-cam.com/video/55lb2KzSiwg/w-d-xo.html

Both designs are allowed. I have a slight (2 degree) taper to my columns to add some stability. Either way can work well.

both allowed balsa engineering says leaning is better idk i just trust him

These mini-towers used 1/8" square legs and 1/32" cross members. If you are looking to replicate a design for this year's Science Olympiad competition, you definitely want to check out my newer videos that go over designs and builds specifically for that. These mini-towers are for demonstration purposes only to show the theory.

I don't quite understand your question. These specific towers are only 25cm tall and are for demonstration purposes only to show the concepts and theory.

@ what if we wanted to do the tower like you then?

@@russelwilson3464 Start with this video for the 2025 season: th-cam.com/video/nA1OLIh1O9w/w-d-xo.html I have 6 or 7 videos each for Div B and Div C. Check those out depending on which division you are to see what I'm doing for this year's specific rules.

@@balsaengineering6686 just checked them out, thanks. I will use your towers as inspiration. one last thing. for the legs what balsa wood should i get. 1/16, 1/8?

@@russelwilson3464 I recommend 1/8" square for the Div B legs. If you are Div C, it's much harder and you'll need to make the legs, but I have a video specifically on how to do that. Good luck!

Hi! All of that information is in my optimization video. Here is a direct link to where I show that in my notebook page: th-cam.com/video/qjI3Yj9Nqc0/w-d-xo.htmlsi=gjjmn9B4pUuU0Cfv&t=464 The cross-member lengths are in blue on the right, in cm.

It depends on the if you are trying to get the bonus or not. The best way to see the exact measurements are to download the zip file with my jig files and load them into a slicer program. This video shows how I came up with the jig designs, and most of the dimensions are shown here as well.

Hi! I encourage you to experiment with that a bit. The rules definitely allow what you are describing. You could have a really long column with a very short base. I think you'll find that any weight you might save with a longer column will be more than used up by needing to make the base stronger due to the increasing leg angles. The base would become much more like a bridge. That is the beauty of testing the bases and columns separately though. See if you can build your short base that holds what you want and within the mass budget that makes it worthwhile. You won't even need to make a complete tower to know if your design change is worthwhile or not. Good luck!!

I found that CA glue doesn't work very well for gluing PLA parts together unless you have much thicker gel based CA. I found PL3 works much better than even gel based CA, but just about any glue that glues plastic should work. If you use any glue that doesn't set quickly (like PL3), make sure you clamp the parts together for best results.

The default nozzle size should be fine to print the jig. This should be a fairly straight forward thing for a printer to print. I suspect something might not be working well with your printer in general. I would recommend trying to print the standard "benchy" torture test first: www.thingiverse.com/thing:763622 Once you dial in the setting with your printer to print that correctly, the column (and just about anything else) should be easy. If you are having trouble printing the boat toy, just do some googling for recommendations. It's pretty much the standard for printer calibration so there are tons of suggestions online based on the problems you'll see when printing that. Good luck!

Hi! I've found in my recent years of building a lot of towers, that it isn't necessary to have the bottom of the legs sanded flat. I always just leave them at an angle and it works fine. That being said, you need to be pretty deliberate to get the legs perfectly aligned from the start. If you check out my assembly video at around the one minute mark, I show how I tape the legs in place on the jig while using a very flat build surface. This works well to make everything nearly perfect: th-cam.com/video/TkUS4W4bOZM/w-d-xo.htmlsi=w-yEqXui0G-rYRWH&t=70

@ oh i see! thank you so much!!

There is a link to a zip file that contains all the jigs and support stl files in the description of this video

@@balsaengineering6686Wait, when I tried downloading the file, I tried opening one of them, but it was read-only and didn’t let me open it. Is there some kind of website or something to actually see the model for downloading? I’m very confused.

@@leodiy7415 Make sure you actually unzip the file on your computer and not just click into it. If you click into it, you can see the files, but they will be limited

⁠@@balsaengineering6686 It worked! Thanks for the fast reply.

There is a link to a zip file that contains all the jigs and support stl files in the description of this video

I don't have a non-bonus Div C jig, but the bonus jig is about 256.5mm at the base

Unfortunately, you can't really "cheat" and use only 3 layers as it will be almost impossible to make a good base strong with that few. I would recommend you watch my 5-part tower basics video series to understand why you need more layers. I would stick to 5. What you need to find is lighter/less dense wood so the weight isn't a problem. If you have the resources, you can buy light density balsa from Specialized Balsa. If you have to buy locally, take a scale with you and buy lighter sheets. Remember that balsa can easily have a density range that is 3-4x, so finding the lighter wood is key once you have your build technique and design mastered. Good luck!

@ thank you

Hi! I don't have a single video that goes over that, but it sounds like you might be struggling with some basic techniques. The key for all of these devices is to get good at precision building. For towers, that means everything needs to be perfectly level for example. Also make sure your gluing technique is good. I do have a dedicated video on that I'd recommend you watch: th-cam.com/video/55lb2KzSiwg/w-d-xo.html Don't get frustrated if your towers aren't perfect right away, it takes a long time to get really good at building these things. The goal is to make progress on each build as you are learning. Good luck!

Hi! Thanks for the kind feedback! I used a free Microsoft tool called 3D Builder to cut the STL into pieces which worked really well: apps.microsoft.com/detail/9wzdncrfj3t6?hl=en-us&gl=US Some people have said it's not available anymore, so maybe it's a Windows 10 only tool, I'm not sure. I have also read that Meshmixer can do that task as well, but haven't used it for that myself: meshmixer.en.softonic.com/ If neither of those work for you, just google "split stl file" and there are plenty of things to try. Good luck!!

Well, that's kinda the whole point of this video. I did what you describe first and it worked, but I would recommend you try taping the jigs together and using it as a guide to help glue it together more accurately. Good luck!

I understood that both techniques worked but I was indecisive about which one to use. Thank you.

@@MayteVidal-y7m It all comes down to what you are more comfortable with. The simpler technique might be fine if you have another person who can hold the column in place, or you can experiment with gluing 1 leg at a time

Thanks! Using 45/45/90 legs could potentially work, for at least 2 of the legs, but you won't be able to build an equilateral tower with just those legs. In a pinch, you could use any legs and just individually sand flat the surfaces needed to attach the cross members. That is certainly not ideal, but might be OK if done carefully. Good luck!!

They will work fine, but you'll probably find that they will be too heavy to achieve a ~2g column if you want to try and match my benchmark build

My partner and I have been using 1/16-inch balsa sheets for cross braces since last year, and we managed to achieve a score above 2,000. I appreciate your input; I'll consider it. Thanks for responding.

Add a horizontal member and maybe a bit more glue, but I think you'll be okay bro. As long as its consistent and strong, you should be ok. Best of luck!

Hi! You may need to rotate the STL files before printing. Your slicer program should be able to do that easily. Just select the object and rotate it, probably just 90 degrees in one direction so it is flat on the printing surface. Good luck!

I just used what I had on hand. For the drywall mesh sander, it was probably around 160-200 grit. I think the rotary sander had 100 grit, and it would probably have been better to use a finer grain as to not sand down the jig as much. Basically, pretty much anything should work if you are careful.

Thanks! I use a moto-tool rotary sander for sanding like that, so it's really no big deal. It's important to leave a little extra so you can make sure it's perfectly flat when you sand it, but feel free to cut the legs a little shorter if you want, especially if you have to sand it by hand.

That’s what I figured too, thanks for the quick response! Cheers 🎉

I just used what I had on hand, which was 100 I believe. Something a bit more fine would probably be better to use.

The base is 24.5cm tall and the column is 26cm. My printer can only print 25cm. You need to have the base a little shorter to give some buffer to follow the 8cm ring rule

I see, thank you, yeah my printer can only do 25cm also