Mass Properties question

[SolidCreative]

Hi, Im trying to calculate the Mass inertia of a tool pivoting on a trunion. Can any explain the difference between these values.

Principal axes of inertia and principal moments of inertia:
Taken at the center of mass.

Moments of inertia:
Taken at the center of mass and aligned with the output coordinate system.

Principal axes of inertia and principal moments of inertia:
Taken at the center of mass.

Units are values: pounds * sq inches


Thanks for any help you may have

Matthew

 

[SolidCreative]

The tool on a trunion will be pivoting around the center of mass. Does that mean i would use principal axis? The second set of values, taken at the center of mass and aligned with out put coordinate system definition kinda confused me

 

[GregLocock]

Firstly, those figures are the second moment of mass

The principal axes of a body are such that the cross coupled terms (Ixy etc) are zero. Typically for a simple symmetrical solid the principal axes are aligned with the 'natural' axes of the body. Even for complex things like a car they are pretty well aligned with the obvious directions.

You need to set up a coordinate system parallel to the axis of rotation, and use that moment of inertia.



Cheers

Greg Locock

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