Have you ever had an old fan with the metal cage still run like a champ but found that a newer plastic fan seems to die within a year or two of usage? Ever been on the freeway and saw someone’s hub cap wobbling and then suddenly fly off? Did you know the earth isn’t a perfect sphere and it’s actually more plump in the middle?
Rotational Mass and Center of Mass play off each other. If the Center of Mass is not perfect on a fan blade or a hub cap it will wiggle itself loose and potentially fail. A lot of design and machining goes into items that spin.
Taking a look back at our Crankshaft example featured in part 1; but this time it’s in an assembly and we can see the COM came in. This COM has a colour change and has the part icon below it. That mean this is the part level COM not the assembly COM. What I recommend is suppressing the COM on the part side so it doesn’t interfere with the assembly COM.
I have these special brass blocks in my assembly. I want to do the Center of Mass, but I don’t want to include these. In order to do this you must bring up the right click menu and select Properties. While the Component Properties is open, on the right side near the bottom, you will see an Envelope check box. Checking this will exclude this part from the COM. This must be done per part and even for any pattern parts.
Any part that’s enveloped will have an icon change in the Design Tree and will change colour in the graphics area. If the colour is interfering with your assembly the envelope colour can be changed in the options.
With the envelope parts out of the way this allows you to add the Center of Mass and do any studies you’d like, such as Motion Study, Design Study or Simulations.