Which Cantilever Design Is More Efficient for a School Project?

[shutout31]

Hi, I'm doing a project for my HS physics class. I need to build a cantilever out of craft sticks (I'm using thin bass wood sticks) that needs to be at least 12 inches long. I'm being graded on the efficiency of it by weight (amount of weight it holds on the end divided by the weight of the cantilever). One end will be fixed while the other end will have the weight at 12 inches out. The teacher will add weight until it breaks. I have two plans that I narrowed it down to but I need your opinion for which design would be more efficient, look here for the rough sketches:

http://images.cardomain.com/member_images/3/web/507000-507999/507399_15_full.jpg

The design will be have two sides like that and single pieces of wood to connect the two.

The other question I have is what angles should I make the triangles? 90-45-45 or 60-60-60?

Thanks in advance.

- Scott

 

[shutout31]

anyone please?

 

[Mr. Robin Parsons]

Your designs are interesting, but you could (probably) use fewer sticksm, I would think...

 

[russ_watters]

Originally posted by Mr. Robin Parsons
Your designs are interesting, but you could (probably) use fewer sticksm, I would think...

Since weight is important, yeah, using less would probably be better. I'm thinking a right triangle with two members glued together cantilevered and one member at say a 45 degree angle up from the end.

If you can pick the cross section, the cantilevered member needs to be about twice as high as it is wide, the two glued together are my way of creating a rectancular cross section beam.

If there are standard length craft sticks or a limit to their length, then my idea becomes a little iffy since stability is best with a single-piece (horizontally) main beam.

 

[shutout31]

I think I get most of what your saying but I'm not familiar with some of the terms you use such as "member" and "rectangular cross section". Is there any way you could do a sketch on microsoft draw or something? I'd really appreciate it. I'm just not good at terms and comprehension. That's why I hate literiture. And in case you were wondering, my ideas are based off this: http://www.brantacan.co.uk/ForthRail.jpg and how a crane is built. Also, the sticks are almost 3 feet long so I think I'm good for any length I need. The sticks are also very light, about the same weight as balsa (slightly more) so I don't think it hurts too much to have a little extra if it does in fact hold more. Thanks a lot for the help everyone.

- Scott

 

[Mr. Robin Parsons]

Since you had mentioned that your mark would be based upon weight of the structure 'divided' by weight that it holds, I had thought you would be looking for the least possible weight of structure, hence "use less sticks" is good advice (right?) Try something like drawing just the bottom half and then a large "A" (or _^ that shape) that has a top that goes twice as high as the height of the body it is spanning, ergo twice a distant upon it's front face as well...means that the top half of the A will stick up above the top flat surface of the (bottom) structure...