|MadSci Network: Engineering|
I tried emailing firstname.lastname@example.org to get a better description of what is meant by an 'egg drop'. No answer in the better part of a week. I'll just assume an 'egg drop' is a competition in building a balsa and string shell around an egg to protect the egg from a given fall. If I'm wrong, sorry, I tried. Although you should start by making best design you know how, you shouldn't count on getting it perfect the first time. The tried and true method of engineering is to build a model and try it out. Today, engineers often use computer models where they used to build physical ones. The underlying process hasn't changed as much as you would think. Way too often, a model doesn't behave exactly the way the designer thought it would. The designer then has to try to change his design to try to improve its observed shortcomings. Then it's time for another test. It's a learning and adapting process. A finished design that an engineer would be satisfied with is usually the end result of many design, test, and evaluation iterations. That said, in an egg drop, the goal is to spread the force of impact over as much area and time as possible. A brief, intense impact, or an impact on a small part of the egg is certain to crack it. You really have a considerable lattitude about how you achieve the goal. You could spread the force out on the surface of the egg with a web of strings woven to resemble several nets holding the egg firmly in place. You could also spread the force over the surface of the egg with a balsa cradle. However the egg is supported, there should be as little slop or looseness between the egg and the holder as is reasonable. Slop results in the egg being jerked around more. In spreading the impact force out over time, it is important is that the finished model have the 'right' amount of give or squishiness. If your model is too rigid, the shock will be transmitted to the egg in a brief, intense instant that will crack the egg. If the model is too squishy, the egg will not decelerate fast enough to avoid smacking your target and breaking. There is a small plateau in between that works right. Cyanoacrylic (super) glue allows quick model construction. Use ventilation. Watch out, it bonds skin really well too. I believe that acetone (nail polish remover) will dissolve cyanoacrylic glue. I'm not sure of the rules in your particular contest, but if weight control of your model is an important consideration, I recommend your last few models use 'six pound' balsa wood. I think that's per cubic foot, but don't get upset if that's not quite right. Common balsa sold in most hobby stores is often about eleven pound grade. In a big city, there likely to be a specialty hobby shop that can get the different grades of balsa. They will likely charge a premium price. The lighter weight balsa isn't as strong as the heavier balsa - but it is stronger for its weight. If you are switching from heavier balsa to lighter, don't forget to use a little more balsa to compensate for the somewhat weaker lightweight balsa. It would be a good idea to videotape your experiments closely. Lighting is important for image quality; in general, use lots of light for better images. If you can borrow an industrial videorecorder rig that takes more pictures in a second than usual (faster frame rate) it will help, but that sounds unlikely. Stepping through your videotape in slow motion will help you see how your shell crushes and what will be needed in the next experiment. Further Reading: Discover Magazine, November 1998, "Light Elements: Precision Package Pounding"
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