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Introduction |
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General Design/Layout - Center of Mass The center of mass is a point associated with an object. This point usually is within the object, but for some shapes is not. If the object were suspended by that point, it would balance, no matter which direction the object were turned. That's a mouthful. For your cars, what it means is that from front to back, it's where the car would balance if a pipe were laid left to right beneath it and pulled up. From left to right, the pipe would go through the balance point, but be laid front to back. From top to bottom, you need to imagine the car rolled over 90 degrees and the balance going front to back through that point. The center of gravity (or mass) is important to aircraft. If the forces are not balanced across the pitch, roll and yaw axis, the plane cannot maintain a straight, flat path. If the balance is way off, the plane goes out of control. Your car has the advantage of having three or four wheels on the ground for stability, but once again, if the balance is too far off - YOU are out of control. The center of mass will be a handy thing to know. Once it has been determined, it can be used in other calculations or investigations. This concept will come up when discussing: · Frame loading as it relates to strength and flex There are different ways to determine this, ranging from non-quantitative physical experimentation, to completely theoretical mathematical modeling. The beginner's exercise will be through non-quantitative physical experimenting, the intermediate will be a little more quantitative and more accurate, and the advanced method will be the most accurate (assuming accurate inputs) and be entirely mathematical. Some of the advanced exercises in this manual are best not attempted by first year students. However, there will be some first year students that may want to work through all parts of this section. A thorough understanding of this concept by at least one team member will be an asset to the overall team effort. If the vehicle were a simple shape, and the same density from one end
to the other - this would be simple. Cars of the same cross section from
one surface to its' opposite would have their centers of mass at the halfway
point. We don't have cars like that though. They are (beautifully) odd
shaped for very good reasons. They are hollow. They have different shaped
"lumps" inside of them of different densities. They just don't
seem to make this figurin' easy at first glance. But it's not as hard
as it might sound. We will break it down into pieces, then model it -
either with "real stuff" (physical modeling), or through calculations
(mathematical modeling) or something a little bit in-between. |
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