## Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

## Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

(OP)

Has anyone noticed a issue in either Creo 2 and 3 (or later versions) that has the product of inertia showing the wrong direction (positive or negative)?

I've found recently that Creo 2 and 3 are reporting the incorrect sign or value (depending on the placement of mass) for the product of inertia and I wanted to confirm if anyone else has seen the same thing.

I created a simple block in exactly the same position, size, orientation, and density in Creo, NX, and Solidworks and ran the mass properties. Creo is the only one reporting the Product of Inertia with negative signs.

I only have access to Creo 2 and 3, so I'm wondering if the same result is seen in Creo 4 and 5?

From my understanding if all the mass is located in the positive X,Y,Z quadrant with a right hand coordinate system, the Product of Inertia should be positive. So that means Creo, at least in 2 and 3, the coordinate system is backwards when outputting the Product of Inertia. For Moment of Inertia there wouldn't be a noticeable difference based on axis +/- direction since the value is always positive. With anyone using later versions of Creo are you also seeing this result?

Thanks!

I've found recently that Creo 2 and 3 are reporting the incorrect sign or value (depending on the placement of mass) for the product of inertia and I wanted to confirm if anyone else has seen the same thing.

I created a simple block in exactly the same position, size, orientation, and density in Creo, NX, and Solidworks and ran the mass properties. Creo is the only one reporting the Product of Inertia with negative signs.

**Please see linked below, PNG image file for those results.**

I only have access to Creo 2 and 3, so I'm wondering if the same result is seen in Creo 4 and 5?

From my understanding if all the mass is located in the positive X,Y,Z quadrant with a right hand coordinate system, the Product of Inertia should be positive. So that means Creo, at least in 2 and 3, the coordinate system is backwards when outputting the Product of Inertia. For Moment of Inertia there wouldn't be a noticeable difference based on axis +/- direction since the value is always positive. With anyone using later versions of Creo are you also seeing this result?

Thanks!

## RE: Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

VOLUME = 1.0000000e+06 INCH^3

SURFACE AREA = 6.0000000e+04 INCH^2

DENSITY = 9.9000000e+01 POUND / INCH^3

MASS = 9.9000000e+07 POUND

CENTER OF GRAVITY with respect to _PRT0002 coordinate frame:

X Y Z 5.0000000e+01 -5.0000000e+01 -5.0000000e+01 INCH

INERTIA with respect to _PRT0002 coordinate frame: (POUND * INCH^2)

INERTIA TENSOR:

Ixx Ixy Ixz 6.6000000e+11 2.4750000e+11 2.4750000e+11

Iyx Iyy Iyz 2.4750000e+11 6.6000000e+11 -2.4750000e+11

Izx Izy Izz 2.4750000e+11 -2.4750000e+11 6.6000000e+11

INERTIA at CENTER OF GRAVITY with respect to _PRT0002 coordinate frame: (POUND * INCH^2)

INERTIA TENSOR:

Ixx Ixy Ixz 1.6500000e+11 0.0000000e+00 0.0000000e+00

Iyx Iyy Iyz 0.0000000e+00 1.6500000e+11 0.0000000e+00

Izx Izy Izz 0.0000000e+00 0.0000000e+00 1.6500000e+11

PRINCIPAL MOMENTS OF INERTIA: (POUND * INCH^2)

I1 I2 I3 1.6500000e+11 1.6500000e+11 1.6500000e+11

ROTATION MATRIX from _PRT0002 orientation to PRINCIPAL AXES:

1.00000 0.00000 0.00000

0.00000 1.00000 0.00000

0.00000 0.00000 1.00000

ROTATION ANGLES from _PRT0002 orientation to PRINCIPAL AXES (degrees):

angles about x y z 0.000 0.000 0.000

RADII OF GYRATION with respect to PRINCIPAL AXES:

R1 R2 R3 4.0824829e+01 4.0824829e+01 4.0824829e+01 INCH

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

## RE: Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

I ask because I see the Iyz as negative, so I'm assuming PTC fixed this issue and the geometry you have shown is different than the example I gave especially with the CG also shown negative in the Y and Z.

Could you match the example or give an image to what those results are based from?

Thanks so much!

## RE: Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

Here are the corrected values.

VOLUME = 1.0000000e+06 INCH^3

SURFACE AREA = 6.0000000e+04 INCH^2

DENSITY = 9.9000000e+01 POUND / INCH^3

MASS = 9.9000000e+07 POUND

CENTER OF GRAVITY with respect to _PRT0002 coordinate frame:

X Y Z 5.0000000e+01 5.0000000e+01 -5.0000000e+01 INCH

INERTIA with respect to _PRT0002 coordinate frame: (POUND * INCH^2)

INERTIA TENSOR:

Ixx Ixy Ixz 6.6000000e+11 -2.4750000e+11 2.4750000e+11

Iyx Iyy Iyz -2.4750000e+11 6.6000000e+11 2.4750000e+11

Izx Izy Izz 2.4750000e+11 2.4750000e+11 6.6000000e+11

INERTIA at CENTER OF GRAVITY with respect to _PRT0002 coordinate frame: (POUND * INCH^2)

INERTIA TENSOR:

Ixx Ixy Ixz 1.6500000e+11 0.0000000e+00 0.0000000e+00

Iyx Iyy Iyz 0.0000000e+00 1.6500000e+11 0.0000000e+00

Izx Izy Izz 0.0000000e+00 0.0000000e+00 1.6500000e+11

PRINCIPAL MOMENTS OF INERTIA: (POUND * INCH^2)

I1 I2 I3 1.6500000e+11 1.6500000e+11 1.6500000e+11

ROTATION MATRIX from _PRT0002 orientation to PRINCIPAL AXES:

1.00000 0.00000 0.00000

0.00000 1.00000 0.00000

0.00000 0.00000 1.00000

ROTATION ANGLES from _PRT0002 orientation to PRINCIPAL AXES (degrees):

angles about x y z 0.000 0.000 0.000

RADII OF GYRATION with respect to PRINCIPAL AXES:

R1 R2 R3 4.0824829e+01 4.0824829e+01 4.0824829e+01 INCH

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

## RE: Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

My first thought would be the first quadrant would be considered all positive.

Thanks!

## RE: Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

## RE: Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

## RE: Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

Given that it's now reporting an incorrect CG with the outputted result showing a negative Z.

CENTER OF GRAVITY with respect to _PRT0002 coordinate frame:X Y Z 5.0000000e+01 5.0000000e+01

-5.0000000e+01INCHThank you again!

## RE: Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

What a nightmare to keep up with from CAD tool to CAD tool.

## RE: Product of Inertia Direction/Sign Incorrect in Creo 2 and 3

For instance you could enter a -20 distance and flip length or direction of offset.

If options were set to

show_dim_sign no

The - sign would be dropped from the dimension and just show the value of 20. I've encountered issues where entering an offset of 0 for a dimension and then entering a value would swap the directionality of the dimension.

UGNX has Top Plane as X-horizontal,Y-vertical with Z in Positive direction.

Front plane faces in the -Ydirection.Pro/E CREO on the other hand Has the Front Plane defined with a X horizontal and Y vertical direction with a Z normal (Facing the front)out of screen.

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