# Towers

 Towers Engineering & Build Event Forum Threads 2017 2012 2011 There are no tests available for this event Images Image Gallery There are no question marathons for this event 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
• 1. Balsa is lighter
• 2. Balsa is easier to bend (more applicable in bridges but it is still important)
• 3. Bass has less variation in each stick of wood.
• 4. Bass is stronger

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: Building Get the Following Recommended Materials===

• Easy Cutter by Midwest (Easy, fast, and clean cuts, even angled) ~$15-$20 on ebay.
Personally, I believe a pack of blades from Rite Aid or Savons is useful too.
• 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 2a: 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.

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 2b: 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.
• If you haven't drawn your plans, STOP! You must go back to 2a.

## Tips and Tricks

• Make the base 16 cm across (don't make it 20cm- if you turn the base, the 16cm should just touch the outside of the square opening)
• Cut a little bit more than you need so that you don't cut too small and waste the wood.
• Make sure you apply only as much glue as you need. You do not want to add too much glue because it will increase the mass of the tower and it will not significantly help it.
• Remember this year's efficiency is different than in years past. You will want as close to 70 cm tall while still maintaining a reasonable mass for the best scores. Although you can have it anywhere from 40-70 cm. There is no penalty for not holding the whole 15 kg.
• Short, light bracings are better than long, heavy bracings.
• When attaching trusses, 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 surface area of contact.
• Remember that using too much bass 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.
• 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. That way you can identify the weak points of your tower
• 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 :)
• sand your tower after its done to make sure all the legs are level

## Scoring

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 $\frac{15,000 \textrm{ g}}{5 \textrm{ g}}=3000$

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.