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Engineering & Build Event
Forum Threads 2017
2012 2011
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Division B Champion Beckendorff Junior High School
Division C Champion Fayetteville-Manlius High School

In Towers, given certain parameters of height, and material, each team is to design, build and test the lightest and tallest tower to carry a maximum standard load. The tower must span an opening (in most years, a 20 cm x 20 cm square), and support a load at a minimum height.

How to Build a Tower


The first issue of tower building is the wood selection. Many consider balsa wood to be the best, followed by bass. However, there are many different opinions on which to use. Here are some opinions:

  • One opinion recommends an all balsa wood tower, but it may be pretty tricky to handle. To use any type of wood, you need an extremely sharp knife for every cut, so as to cut the wood and not smash the wood fibers (A blade will have a lot of life left after you change it for tower building, and one way to save costs is to save the blades and use them later for other projects, etc.). Smashing the wood fibers damages the integrity of the wood and hurts your score.
  • Another opinion states that heavy bass wood should be used first when you are trying to understand the dynamics of the structure. Once you have a working design using bass wood, you can then cut off weight by using smaller sizes or balsa. Using balsa can make it more difficult if it is your first time.
  • Another opinion suggest that you can have a mix of balsa and bass. Where you need the extra strength you can use bass. In all other places balsa is fine. The legs are normally bass and bracings balsa. A mix of the two brings out the best of both in one tower.

Balsa vs. Bass:

  • Balsa is on average lighter for a specific strength, although individual pieces vary in both woods
  • Balsa is easier to bend. This is generally not relevant in Towers, but may be important for some specialized designs.
  • Bass has less variation between pieces than balsa with regard to the range of density for a certain size, and the range of strength for a specific density.
  • Bass is generally stronger for a certain size, though usually heavier as well.

Step 1

  • The next step is design. A four legged tower is easier to build but may not be as efficient. A 3 legged tower is extremely difficult to build, as the angles aren't nice and neat. Furthermore, a bracing strip needs to be angled 2 ways, whereas in a 4 legged design it only needs to be angled in one direction. Also, don't forget about laminating wood together- many good towers have been built by laminating very small wood together for the legs. You should also consider the height. This years rules put an emphasis on a taller tower. Although a taller tower may be harder to construct to still hold enough, it may be worth it because the advantage is big enough.
  • After you've decided on the number of legs, the bracing is the part that towers are won and lost by. It depends on the type of leg design you use, but generally balsa wood legs of dimensions 3/16x1/8cm need to be braced every 5 or 6cm all
    the way up (by the way, a solid wood square is not the best way to go for legs). Also, with the bracing, equality is of high importance. If you brace at 5cm and then the next space is 8cm, you're testing the 8cm space. It would be better to brace at 6.5 cm and 6.5 cm in this example.
  • In addition, you must decide on if you want to build a rectangular base or a square base if you are created a four legged tower. A rectangular base tower needs stiffer legs and are lighter, but they have a high change of tipping over. A way to cure this(Though will add weight) is to slant the wide side of the tower until it almost forms a pyramid.
  • Other than this, the only advice I can give you is test, test, and test some more. The more you build, the better your chances of getting a good design, and the better you get at building. Analyze your failed structures. Knowing which member broke first (you can tell by the type of break, sheer, torque (twisting),or bending) will tell you what piece of wood needs to be more dense, or larger in cross section. It is a very good idea to understand how the stresses are flowing in your tower. Eventually, time spent on building individual towers will decrease, while the quality will increase. Also, never test towers over the maximum weight that the rules say. If it holds, set it aside and see where you can cut back. If you fail, then you still have a backup.

Step 2a: Materials

Get the Following Recommended Materials:

  • Easy Cutter by Midwest (Easy, fast, and clean cuts, even angled) ~$15-$20 on ebay.
    • A pack of extra blades may also be useful
  • 1/8 and 1/16 BalsaWood. (Make sure the 1/16 isn't too flimsy and cheap)
  • Zap-A-Gap glue (reasonably strong, and fast curing)

Step 2b: Design

So how should you build your tower? The best way is to really create a full scale blueprint on graph paper. First of all, you should think of a more general design and draw it out. Here was my basic design for 2006.

Tower 4285.jpg

Once you have that you should continue on and draw it out on graph paper. It makes it a lot easier if you create a "jig" of your blueprint. In other words, use pieces of scrap wood to create a template shown below:

(picture to come)

The jig makes it possible for concise construction of the tower, ensuring it will not be slanted.

Step 2c: Bracings

Once you have the design of your tower fully planned out, it is time to know what type of bracing to use.

  • One idea suggests using an X Brace, where two pieces of wood cross over each other, creating an X. The advantage of this method is that it will prevent the legs from bowing outwards and slightly inwards, but at the cost of more wood.
  • The second idea mentions using A Z Brace, where a diagonal piece of wood lies in between two horizontal members. The benefit to having this is that the side will be held together, but will start to torque in the direction of the diagonal brace.
  • Another method is to use Z Bracings without the horizonal members, similar to this(Imagine the chimney on its side): |/\/\/\/\/\/\|. The benefit to having this is that it requires less wood and almost provides as much support as the Z Brace. However, since there is no horizontal brace to keep the tower from bowing inwards, you would need to angle the bracings at a smaller angle and have a medium-high density wood.
  • There are many other types of bracings, such as the V brace and the /\ brace, too. However,their scores in the previous years are not too high, so these types of bracings are much better to use.

Step 3: Construction

  • Construction is rather easy with an easy cutter and plans with measurements. All you have to do now is to cut all the pieces out that you have measured, although this can take up hours if you have never done it before. Remember to cut out 4x the wood on the bluprint, then you connect the two halves with bracings that form the 3rd and 4th sides.
  • I believe the most important thing about Tower Building is the straightness of it. If balance is off and the weight is not distributed equally it will fail when using lighter smaller wood.
  • You should make your loading block support hole a little smaller so the loading block can't slip and fall.
  • If you haven't drawn your plans, STOP! You must go back to 2a.

Tips and Tricks

  • The Test Base opening is typically a square of 20 cm sides. This means that a tower with a base of 15 or 16 cm can be oriented so that each leg rests at the midpoint of the opening's sides, rather than building a tower with a base of 20 or 21 cm with the legs resting at the corners.
  • It is far more difficult to increase the size of a stick than to decrease the size. Hence, cut sticks so that there is some extra length, making it easier to adjust - if you mess up and cut a stick too short, there's no way to correct it.
  • Make sure you apply only as much glue as you need - in most cases, significantly less than one drop. You do not want to add too much glue because it will increase the mass of the tower and it will not significantly increae the strength - in an adequately constructed tower, the glue joints are among the strongest parts. The faces being glued to each other should be as flat as possible to minimize the amount of space-filling done with glue.
  • Short, light bracings are better than long, heavy bracings.
  • When attaching braces, make sure to glue them on top of the frame as opposed to adjacent to the frame. It makes the tower MUCH MUCH stronger because it provides a greater contact area.
  • Remember that using too much wood will weigh down your tower and hurt your score. Most winning towers win because of their weight, so even if you do hold all 15 kg your score will rely more on your weight.
  • Ideally, the load should be equally distributed across each leg of the tower. To help the tower rest on the test base more evenly, sanding the bottom of the legs can be helpful. However, be careful not to end up with a tower that is shorter than the minimum allowed height.
  • Don't forget that if your tower's base is 29 cm wide, you will get a score bonus. Of course, this isn't always recommended so build at your own score risk. If you do decide to get the bonus, remember that your tower will be weaker. You should also be sure that your base is a little bigger than the requirement so that you won't risk the potential bonus and weaken your tower for nothing.
  • Build on a consistent basis and test regularly
  • Take a slow-motion video of your tower while you test it. Towers typically begin failing at a single point, which cascades into a failure of other members. A slow-motion video makes it easier to identify the point of failure and fix/improve it.
  • NEVER GIVE UP! Towers is a frustrating event in which you have to build many towers to suceed. Don't give up and keep persevering. The reward is satisfying :)


A tower is scored primarily according to its efficiency - load held mass divided by the mass of the tower. For example, a tower that weighs 5 grams and holds 15 kilograms would earn a score of [math]\frac{15,000 \textrm{ g}}{5 \textrm{ g}}=3000[/math]

The maximum "load held" is 15 kilograms.

In most years, there are additional factors that affect the score:

  • In 2017, there was a bonus awarded if the tower spanned a 29cm circle centered on the 20cm by 20cm opening. The bonus added 2000 grams to "mass held".
  • In 2012, the tower efficiency was weighted by the height of the tower. The specific weight depended on the tournament level (regional, state, national), such that at higher tournament levels a corresponding increase in height would have a greater impact on the score, encouraging taller towers at higher levels of competition.
  • In 2011, the score was calculated using the square of the load held, in kilograms, divided by the mass of the tower in grams.

Competitiveness of teams in Towers at different tournaments varies greatly. As of the 2017 season, in the majority of states a score of 1000 is sufficient to finish near the top 4-6. In some larger states, high scores reach 2500+, or even 3000+. At the 2017 National Tournament, the medaling scores were approximately 2900-3500 in Division B, and 2700-3300 in Division C.

Useful Threads

From 2006:

From 2005:

From 2004:

External Links