Recommended quantity of balsa

[jmillard]

I'm a teacher in the Philadelphia district and I want to do a small, mock event that mirrors this competition. I've found a good supplier for the balsa wood but I'm not sure exactly how much to purchase. If i assume I just give my students 1/32 balsa sticks, how much do you all think one tower would take? Should i order for two towers each to account for testing? Any sort of advice would be awesome, I want my students to have a great end of the year physics project.

[Matholy]

I would suggests buying bulk quantities from amazon, or if you really want good quality wood, specializedbalsa. If you don't want to buy it online, go to any hobby store like Hobby Lobby to buy balsa, but this wood is usually not that good.

I would suggest altering the rules to make the building process easier: if you use last year's rules, the tower is 1 piece, instead of a 2 piece tower, with a top and bottom (this year's rules).

Also, most balsa is sold in 36 sticks, so I would suggest that you can fit 2 of the columns into the 1 stick to save wood. You should make the rules so that the tower needs to be 40cm, instead of 50cm in the rules. (2 columns * 40cm = 80cm = about 31 inches, with about 4 inches to spare).

Therefore, for each tower, you need 2 sticks for the columns (I would suggest 1/8, or maybe 3/16), and maybe 10 sticks of 1/16 for each pair (all 36 inch).

Always buy extra. I suggest you buy maybe 25% more of the 1/8 or 3/16, and maybe 30-40% more for the 1/16 sticks.

[Crtomir]

I'm a teacher in the Philadelphia district and I want to do a small, mock event that mirrors this competition. I've found a good supplier for the balsa wood but I'm not sure exactly how much to purchase. If i assume I just give my students 1/32 balsa sticks, how much do you all think one tower would take? Should i order for two towers each to account for testing? Any sort of advice would be awesome, I want my students to have a great end of the year physics project.

For the main (4) columns (legs) of the tower, I would recommend using 1/8" x 1/8" x 36" sticks. Have the kids weigh them and choose four that weigh the same (to the nearest tenth of a gram). I would start heavier (like 2.0g for 1/8" x 1/8" x 36") and then work your way lighter to maybe 1.5g per stick. You can go lighter than that even. 1.0g per stick is probably what some of the best teams are using.

For the braces, the easiest thing is to buy 1/16" thick sheets that are 36" long and either 3" or 4" wide. Then you use a balsa stripper, like this one https://www.amazon.com/Master-Airscrew- ... a+stripper, to cut strips that are 1/16" thick, 36" long, and somewhere between 1/32" and 1/16" wide. These should weigh between 0.20g and 0.30g for each 36" strip.

The easiest bracing scheme is to do all X-braces. So mark off equal intervals on the 1/8" x 1/8" columns and put X-braces all the way up. The key thing is that as the density of your columns goes down (weight of column pieces goes down), the number of bracing intervals you need goes up. For 1/8" x 1/8" x 36" sticks, if they weigh 2.0g each, you probably only need 5 bracing intervals, but if they weigh 1.0g each, you might need 9-11 bracing intervals.

The other thing that would be really helpful is a jig to build on. That way, the kids can build it up in 3D, rather than building two sides separately and then trying to put them together later. I have a picture of the jig our team used last year here: https://www.dropbox.com/sh/7cjwsh032byl ... hEx1a?dl=0. Also, there are some other interesting documents in that folder that you could use to teach your students more about towers.

Hope this helps.

[Crtomir]

So for the short answer:

For one tower:

4 sticks of equal weight that are 1/8" x 1/8" x 36"
1 sheet of 1/16" x 4" x 36"

But if you want exact densities (you will eventually want this), you will either need to special order or order a lot and down-select yourself.

[DarthBuilder]

worse come to worse, you can just buy the kit on the scioly store/ wards science.