Weight for Main Compression and Tension Chords?

[FrogLegs]

What weight balsa or bass are you using for your main compression chords? I suspect we (being accustomed to building light towers and bridges) are starting too low with around 1g balsa for the main compression and tension pieces. I am thinking of having my students bump up to 2g balsa per stick as most students aren't able to reach Tier 1 at this point.

[Cow481]

What weight balsa or bass are you using for your main compression chords? I suspect we (being accustomed to building light towers and bridges) are starting too low with around 1g balsa for the main compression and tension pieces. I am thinking of having my students bump up to 2g balsa per stick as most students aren't able to reach Tier 1 at this point.

I have been using around 5 grams per 48 inch for compression and around 1.5 grams per 48 inch for tension and have been getting over 1000 score

[dholdgreve]

While weight and stiffness are somewhat proportional, there is no direct correlation. You may be better off identifying the stiffness required of the compression beams as opposed to the weight. Using the stiffness (SFPD for those that have followed Balsaman in the past), you can utilize Euler's buckling theory to determine the bracing required in both the vertical and horizontal axis. Keep in mind that although you are loading with 15 kg, the boom will suffer from mechanical disadvantage (40 cm extension, 20 cm height) so the loads imposed with twice the vertical load, so design for 15 kg ON EACH COMPRESSION BEAM. For those new to structures this year, I'd suggest that you do a search for Euler in the tower thread from last year. The same principles apply to boom this year!