Hi! If you have the choice between using an auto-load and hand-loading you'll always want to choose the auto-loader. The main goal when loading is to minimize the time under load and when you hand load, there will always be a time your device is under load while you are refilling the cup/scoop. When using an auto-loader, you can keep a stream of sand going all the time, and you want to keep that going pretty fast especially near the end. Scores are typically a bit higher with an auto-loader for that reason. If everyone is forced to hand load, try to refill the cup/scoop as fast as possible and pour quickly (within reason) as well. The excess force of the sand moving faster from a higher height is not an issue to worry about and is counter-acted by the huge benefit of minimizing the time near max load. Good luck!

Hi! A couple things... I don't sell anything... you can replicate this build with all the information I provide in my various videos. Second, this tower is from last year and the rules are different this year, so if you are competing now, you don't want to copy this build. Check out my 2025 videos for the newest version. Good luck!

Not exactly... they were created using 3/16 x 3/16 source sticks and then sanded down to 60/60/60 triangles which makes them much smaller. Check out this video for all the details: kzbin.info/www/bejne/g4Wrqpquirhmj7c

Please watch my videos where I go over the rules for this year. There I show how I used the ring along with my jigs to know the final tower will be compliant. You should definitely test your towers with a ring before any official competition if you are unsure.

Hi! Sure, you'll have no problems using a slightly heavier leg in the build. Just remember that your tower will only be as strong as your weakest leg, so that heavy leg will be fine, but it will just add a bit of excess weight to your tower compared to what it could have been. Good luck!!

Hi okay thank you so much, also after I'm done building my tower should I sand my legs to the same level as my horizontal bracing or should the legs be higher than the horizontal bracings? Finally you have any tips to keep the bucket balanced when loading the sand using a machine. Thanks

@@asteralemayehu4973 You shouldn't need to sand the bottom of the tower at all, just leave the legs a bit longer than the cross bracing. As for the bucket, my recommendation is to start fairly slow for maybe 5-10 seconds, but soon after that get to pretty much maximum loading speed. You want to limit the time under heavy load as much as possible. Good luck!

You can definitely use 1/4" balsa when building the tower. You will probably find that it is overkill, meaning your tower will be pretty heavy, but it's fine to use especially if you are just starting out. Good luck!

The answer is I'm not 100% sure. They may or may not be depending on how strong the legs and top cross bracing pieces are. I decided to keep this build fairly conservative and include both the bottom and top horizontal cross members. Those are both things you should experiment with as you iterate with your builds! Good luck!!

Thanks! Love your videos!❤

Hi! If you check out the video at the 4:51 mark, you can see my notebook page for the benchmark build. There you can see the masses of all the parts including the legs and each cross bracing layer in written in red. The measurements on the right for the cross bracing are for all 8 pieces of a layer together, so for example, the bottom layer used (8) pieces that were 20.3cm long each and together they all weighed 0.492g.

Hi! Yes, with the exact same dimensions, balsa wood can have a HUGE range of densities. Check out this video when you get a chance to see what I'm talking about in more detail: kzbin.info/www/bejne/o6uwd5uaabikhpo

Check out this video for how I strip my balsa sheets: kzbin.info/www/bejne/mH3WhYKmotStfas You can use a very inexpensive screw stripper you can buy on Amazon. You should be able to find 1/16" sheet balsa fairly easy, but maybe not in the density you want. Worse case, you can use 1/8" sticks. You probably wouldn't need to make Xes with them except maybe for the bottom couple layers. If you can't find 1/16" but buy the stripping tool, you could cut 1/16" strips from your 1/8" sheet which would at least be half the mass of 1/8" sticks. Good luck!!

@@balsaengineering6686 Thank you so much. you're my hero

Thanks! If you are asking if the base and column need to have cross-bracing between the legs, the answer is definitely. The X design is only one option, although probably the best option. If you want to learn the theory behind this and see some other examples, I recommend you watch my 5-part Tower Basics series where I explain all of that. Here is part 1: kzbin.info/www/bejne/jn3Xn2ucp96aj9E Good luck this season!

I understand but if we don’t do cross bracing will it be disqualified?​@@balsaengineering6686

I don't really know what you mean when you say a slanted top. Both the column and the base need to hold the same amount of weight and ideally you want that weight transfer from the column to the base to be as symmetric as possible. If your column always holds and your base always fails, I recommend you start testing them separately and lower the mass of the column and/or increase the base strength until they are a better match to each other. The key to the perfect tower is having those components be perfectly matched in strength. Good luck this season!

@balsaengineering6686 Thank you very much for the insight!

You can compute the exact densities from the information I show in my notebook at 6:56. I show the dimensions and mass, so if you convert the units properly, you can calculate the exact densities if you want. In general, the cross bracing was "light" density and the source 3/16 sticks were "medium". Good luck!

The ring doesn't have to be at exactly 25cm only, it just need to be able to fit AT 25cm. For example, your device could allow the ring to be all the way down to 15cm from the base bottom, but that also means it would easily fit at 25cm from the bottom. Generally though, you will find that it's more optimal to design that ring clearance to be as close to the maximum height as possible, but definitely experiment with it on your own!

⁠@@balsaengineering6686 Thank you so much. So far it's close to 25cm. Your videos are a great help. We won 4th place at Rockford and 5th place at Kildmas invitationals.

@@IYASisters No problem. Congrats on your recent results! Keep up the good work!

Yes, a 3-sided tower is definitely allowed if it follows all the other rules. They are typically much more difficult to build which is why I’d generally recommend 4-sided when possible. See some of my Div C videos for what some of those challenges are as 3-sided is required for that division this year

Hi! Congrats on your build, that is a very good result! Part of the fun of this event is experimenting with the types of things you are talking about. I would definitely recommend you experiment with different sizes and densities for future builds. From the various scores around the country, we know that sub 5.5g (and even lower) towers are possible, so keep doing what you can to try and optimize your material to get as close to that as possible. Good luck!!

Thank you so much for the quick response! I’ll experiment it then and see how it goes :)

​@@balsaengineering6686 Are said sub 5.5 gram towers going for the bonus? If so, nationals sure will be interesting this year!

Hi! For Div C this year, I only had to make 5 towers to get to my benchmark build. I would imagine I'd need another 5-10 builds to really do final optimization and then multiple builds for each important competition to choose the best one. You are definitely right wrt time to build these towers. It takes me about 3 hours each, not counting material selection and library creation. The year I built 96 bridges, and our team as a whole was probably close to 200, we were really figuring things out from scratch, including a decent design. Once you have a good base design, that can cut down a lot of extra work. You still need to do a ton of work to gain build skills and material optimization, but there is less time spent on building "bad" designs. That is one of the primary reasons for my channel... I want students to be able to build 20-30 devices and be able to compete at the highest level instead of hundreds (even 100s only works with some guidance, trial and error on the design from scratch is not enough). Anyway, back to your question, the number of towers you'll need to build will vary on a lot of factors, but it sounds like you have the build skills down with 23 towers already, so the next dozen or so should get you to where you want to be if you have the ability to analyze the failures with high speed video. Good luck!! (BTW, if you are having trouble optimizing your design, be sure to check out my older series on advanced optimization techniques. it was made using bridges, but the concepts apply for all these devices)

@@balsaengineering6686 Another question: I've recently gotten my hands on a scale that is precise down to milligrams, and what I've discovered is that large fluctuations in weight distribution are not just existent in sheets and sticks, but that they also exist down to individual members themselves, and by a considerable amount. What I'd like to know is, what percent margin of error do you typically find acceptable for deviations in weight on a member to member basis? For example, if I am on the 4th tier of my tower, and my cross member's have an average mass of .06 grams, would you find it unacceptable to include a member that weighs .054 grams in that layer? A 10% deviation in mass is a considerable amount, especially at such a small scale, and I could find it reasonable to assume that such a deviation could induce disproportional axial loads, resulting in a premature failure.

@@Justin-x6b7h That's a good question... generally, I try and keep things within about 10% or so. Often I only weigh all the cross members of a layer together and just make sure as a group they are increasing or decreasing like I expect. You are right though, balsa is really not consistent and ideally you'd weigh every single piece with a milligram accurate scale. I have one which is really nice, but it's also nearly $500, so I try and show techniques that don't require that kind of precision, but if you have access to one, by all means work to get every single piece as close to each other as possible.

Hi! Yep, we basically used the same technique for transport for all of these devices. In my Competition Prep video I demonstrate the technique with a bridge, but that's what we did for tower as well: kzbin.info/www/bejne/bKuyp3uDj7GUhKc (Note that we always were able to drive our devices in a car to competitions. If you have to pack it for more rough travel, you might want to consider something else)

Hi! Thanks for the kind feedback! I think the bottom horizontal cross members may or may not be needed depending on how strong the rest of your lower cross bracing is. My benchmark build took a more conservative approach and included it, but I encourage you to experiment and tweak the design based on the materials you have on hand. I don't know the exact density of the 1/16" I used off-hand, but it was definitely in the "light" range. You can compute the exact density for every layer if you want given what I show in my notes (exact dimensions and mass - just be sure to convert the units properly)

It definitely helps keep the base of the tower legs from splitting apart. The amount that it's required will depend on a lot of factors most directly, how strong those bottom cross-member X pieces are. That is something to play around with when optimizing your build with the material you have on hand. For a non-bonus build, I would definitely experiment if it's required or not. It is probably more useful for a bonus build due to the larger size. You can also experiment with the cross members at the top of the base. I have a feeling those are required, but that might be able to be scaled back. I didn't do a full optimization of this design, so there is room for improvement!! Good luck!

Why do you think the top horizontal bracing is required and what does it do?

@@lukeherring1769 Just to clarify, top of the base, not top of the column. I have seen some bases fail by caving in at the top. These horizontal pieces prevent that. What I don't know is what the minimum dimension/mass needs to be. Or potentially they aren't needed depending on the mass of your base legs and the upper base cross members. This is all part of the overall optimization task. Good luck!!

Thank you!

There are no direct links to the pieces like that. You will have to buy "light" density balsa sheets and cut your own sticks to get exactly what you want. That is exactly how I do it. I like to buy my balsa sheets from Specialized Balsa: specializedbalsa.com/products/balsa_sheets.php

There are no direct links to the pieces like that. You will have to buy "light" density balsa sheets and cut your own sticks to get exactly what you want. That is exactly how I do it. I like to buy my balsa sheets from Specialized Balsa: specializedbalsa.com/products/balsa_sheets.php

I can't remember exactly, but for this particular jig, I think I used something like 40 or 50% infill because I knew I would be sanding it down and wanted it to be as strong as possible. I would imagine the default 20% would be fine though. I would recommend printing a small test extrusion of say 20mm to test your print settings and see how that works before printing the full thing.

Hi! Thanks for the kind feedback! These jig stl files are the exact ones I used to print and use and what I'm showing in my videos. The only thing I can think of is perhaps your printer scaled the base down a tiny bit. Make sure your finished base height is exactly 245mm and the column pieces are 130mm each in Z. In the 3d printer scaler program, make sure they are at 100% size. If your print volume isn't large enough for the base, you can cut it into 2 pieces with a program like Microsoft's free 3D Builder app. Good luck!!

Thanks for the tips! Measured the pieces and they're exactly 24.5 and 13 cm respectively. Was looking at the STL dimensions for the bottom column and the corners, not where the 1/8 stick goes, but the pop outs from the main column has different measurements. Range from 6.x mm to 7.x mm. No worries, we'll figure it out, thanks again.

Thank you so much for the kind feedback, it means a lot to me! Congratulations on your first place finish!!

Hi! I always cut my own sticks from sheets. It's WAY more cost effective and you can have more control if you want to use non-standard sizes. I don't sand these at all though. These towers take a long time to build, so don't feel bad. It probably takes me about 3 hrs total to build one and that doesn't count the time for material creation/selection. You'll get faster with each one you make! Good luck!!

For most things, I just use a simple/inexpensive airscrew stripper like this: www.amazon.com/dp/B0000WS5OQ Be sure to check out my video on creating a balsa library to see it in action and for a few tips on using it: kzbin.info/www/bejne/mH3WhYKmotStfassi=003dLUcqBb6vT0rA

@@balsaengineering6686 Thank you!!

Hi! Not really... it doesn't have to be a fancy auto-loader like I am showing here, but a bucket with sand is about the cheapest/easiest way to do it. You'll definitely want to test with a 5x5x2cm loading block because that's what you'll use in competition, so you want to make sure there are no surprises on test day!

You'll definitely want to buy sheets and cut the strips yourself. It WAY more cost effective to do that.

This build used 1/32" thick by 1.25mm wide (custom cut from sheet)

Hi! I don't really understand your question. If you have a slightly different tower design, for the cross-members, you'll first need to figure out how long to make them. For the other dimensions, you can probably start with what I have shown in my various videos. A good start is always 1/16 x 1/16, especially for the base. Good luck!!

Thanks for the kind feedback! You could try and do the math accounting for the angle of the legs, but to be honest, the way I do it is to print the jig first, mark 2 legs at the cross-member layer interval I want, tape those to the jig and then measure the distance of all the cross-member pieces. It's simple and I'm less likely to make a mistake that way :)

Ok, thank you so much for the tips!

Yes, that is what I did for my benchmark tower you see here. There is no one correct answer though, so depending on your legs, you might want to experiment with more or fewer layers and the spacing will change accordingly.

@@balsaengineering6686 Thank you!

In other videos I show my notebook page where I show that I like to pre-cut the lengths of the legs to 52.5cm which gives a bit of a buffer to sand after it's assembled on the jig.

Unfortunately, it's going to be very hard to use 1/8" sticks for this build. If you create something to shave them down to 60/60/60 triangles, it's going to be less than half the original cross sectional area. That is going to be much too small unless these sticks were really heavy to start. Even then, I wouldn't recommend that. The easiest solution if at all possible, would be to try and get some 3/16" wood to work with. 1/4" is also an option if that's all you can find. It'd be easy to scale up the sanding jig a tiny bit to use 1/4" wood. If none of that is an option, you could glue (4) 1/8" sticks together to make 1/4" and then sand that down. Certainly not ideal, but possible if that's all you have to work with

My best suggestion for that would be to make sure you are building the tower on a perfectly flat surface like the ceramic tile I show in my videos. It really helps compared to something like a conventional table. Take the time to tape the legs in place and touching the surface while the jig is vertical and you shouldn't have those types of issues. It does take some practice to get that technique down, so don't get discouraged if you don't get it the first time.

Are you sure you want last year’s jig? If not, check out the 2025 videos and the jigs are in a zip file in the description

You can certainly try it if you have access to circular balsa that is in a good weight range. You would only have the very small tangent area to glue your cross bracing though, so that might not work very well. Let me know how it works if you give it a try!

Hi! I admit that for every competition we attended when I was a coach, the bin was driven in a personal vehicle. No buses that I can remember. There is nothing wrong with making a more secure travel bin, just be careful when pulling the device out if you use any sort of packing material (it sounds like you don't). I have seen some teams have damage when pulling a fragile device out when they used peanuts for packing which I would not recommend. Something like 1/32" cross bracing can be very fragile and you don't want anything touching that if at all possible.

@balsaengineering6686 Sorry, I forgot to mention that I do use just a bit of bubble wrap. But a personal vehicle probably eliminated that issue for you guys :⁠-⁠). I do appreciate the reminder for carefulneds while taking it out. What really ticks me is when I see teams going to the building for testing towers at university comps and they are holding the tower in their hands and just strolling along. One trip and all the hard work is down the drain.

@@completeandabsolutenerd Oh yeah, I saw that all the time too! Not only are you risking breaking it if you trip or bump into something, you are allowing it to absorb all sorts of moisture. Of course, the teams walking with a device just strolling along aren't typically the same teams that are worried about gaining 3% mass which might cost them 1st place :)

@balsaengineering6686 Whenever I see a team like that, I can pretty much tell whos going to be competition for me and who's not.

Hi! Thanks for the kind feedback! The reason the legs needs to be triangular are that you really want flat surfaces to glue the cross-members to. Square legs won't allow that. It might be possible to sand down just the joint locations individually, but that won't be easy or particularly reliable. Try to assemble a 3-leg tower with square legs and you'll see what I'm talking about :)

That is almost always fine to do. Over the years, my team used several devices multiple times without any problem. I would recommend you pre-test that device again to make sure there wasn't any damage done by the first test. Usually damage occurs if it's very close to its maximum breaking load. You should definitely be able to pre-test to ~12kg to verify it's still fine. If you want to be absolutely sure, you could pre-test to 15kg and then again to 12kg. If it survives that, it's almost certain it will hold 15kg again.

@@balsaengineering6686 Great, thank you so much! I will let you know how this turns out at the end of our season!

Hi! I don't sell the printed jigs, but you can download the stl files in the description of this video. You can either print them yourself or potentially use a 3rd party online service to print them, but I would recommend you find a local option if possible.

Thanks a lot.

I like to buy my balsa in sheets from Specialized Balsa: specializedbalsa.com/products/balsa_sheets.php The legs were from 3/16" sheets (cut square and then sanded into 60/60/60 triangles ). The cross-members were from 1/16" sheet, although 1/20" is also worth experimenting with

@@balsaengineering6686 thx so much for the reply

do you have to sand them into triangles? how would it affect the performance if you leave it as a square (i am looking at buying the precut ones)

@@Cloudyedits3579 The problem with leaving them square isn't about performance, but geometry. You can't use square legs and have flat surfaces to glue the cross-members on to when the tower is an equilateral triangle. Check out this video for more details: kzbin.info/www/bejne/lYK3gHZ_faqSZ9k

Really light balsa is very squishy to the touch. That is usually a sign it’s too light, but it depends on the application. If the mass is close to what I showed, it will probably be fine

@ it’s 1/8x1/8 weighs .6g 24 inch is this fine?

@@Fire_World428 That would make it around 0.26g for my normalized length of 26.5cm which I use for both the columns and bases. So, that would be heavier than the wood I used for the columns (around 0.224g each) and lighter than the wood I used for the base legs (around 0.35g each). I would say that wood is probably fine for the column legs, but might be too light for the base.

@ I built a top today using the 1/8 and 1/16 for crosses gave up at 12.8kg

Hi! Congrats on your results! This is the exact scale I am using: www.amazon.com/Ohaus-SPX123-Portable-Balance-0-001g/dp/B01AJ089PS I realize that it is quite expensive and not for everyone. For measuring the cross members, I would recommend you weigh them in groups, so like all 8 pieces for a given layer at a time. Less expensive scales should be able to be pretty accurate for that. Try to use other methods to see if there are any outliers in the group, either visually or by holding them. If one of the 8 seem out of place, either too heavy or too light (or not cut perfectly), just replace it. It's pretty important to have these as consistent as possible. Good luck!!