![]() ![]() For a set of discreet masses it is simply the sum of the massese multiplied by their (perpendicular) distance from the axis squared. I'd suggest that whilst a CAD program is the quickest way to get a value once you have a model that is accurate, it is beneficial to know the theory behind what you're doing - at least then if you get obviously silly numbers you realise and try to solve it! For example, are the origin of the axes in your model in the right place? Translating an axis about which you're finding the moment of inertia will change its value.Īs JTom said, effectively all you need is Mr^2. Voilá.īORING NOTE: notice AutoCAD uses the terminology of "Moment of inertia" for the Second Moment of Inertia (the one that is used to calculate bendings), while it calls "Principal Moment of Inertia" to the Mass Moment of Inertia (the one used to calculate rotations, the one you need). Simply "apply" a material, including density, to each part of the car. If you wish you can do the same with the engine or other components, by density. Here you have the answer for the three axes (yaw, etc.). ![]() Then I used the LOFT command to create the volume of the car (LOFT and then click on each polyline). If you're sophisticated, you can draw a "path" that joins the two copies, but I kept it simple. Then I copied the polyline to create two separate images of the car (COPY, using a frontal view). Then I exploded the block (command EXPLODE), converted the edge to a polyline (PEDIT and then Yes). I first took a sideview of a car that is interred somewhere in the Design Center (you can use your own drawing). Now, for a car (sorry, is solid as the sphere, I made a mess of myself trying to use the SHELL command, to produce a hollow car, but perhaps you know or can consult how to do it): I check against the formula, assuming that the density is equal to 1 (water). I draw a sphere, 2 m radius and then I click on Tools/Inquiry/ and then in Region/Mass Properties. ![]()
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