topic Re: Rotate about the COG in Inventor Forum

Rotate about the COG

Thegreatrandino — Mon, 15 Mar 2021 18:14:58 GMT

I have a part and I've drawn a line through the COG and I would like to rotate the part such that the line through the COF is vertical, or plumb.

I selected view Center of Gravity, selected it, and recorded the coordinates. I create new sketch on the part and put a point with the precise input. Next I constrained the point with a lock. Then I line from the center of a hole at the top of the part, past the COG point. The line is coincident to the center of the hole at the top. Next I placed a coincident constraint on the COG point and the Line. Now how do I rotate it so that the line is vertical?

When the line is vertical, I can put a circle on the line so that the circle, the COG, and the hole at the top are all vertically aligned.

Re: Rotate about the COG

foolishgrunt — Mon, 15 Mar 2021 19:41:39 GMT

Dunno if I completely understood your question. But here's what I did.

Copy/paste the COG point from sketch 2 into sketch 1. Redraw your line. Add a few dimensions from your radius centers to the COG point to keep the outline rigid in respect to the line. Add a vertical constraint to your line.

Re: Rotate about the COG

Thegreatrandino — Mon, 15 Mar 2021 20:33:03 GMT

Thanks for the quick reply. It's upside down!!!! GRIN!!!

It "hangs" from the hole at the top. So there is a plumb line, or vertical line, from the center of the hole through the CoG point. I want to add a peg, or circle in line with this same line. (Sorry if I'm stating the obvious about the CoG, it just helps me to understand when I explain it)

Did you rotate the part? Never though to try copy/paste. Does the paste put it at some coordinates

Re: Rotate about the COG

foolishgrunt — Mon, 15 Mar 2021 20:44:48 GMT

Yes, copy/pasting a sketch feature will maintain the exact same distance from the origin in the new sketch as it had in the old sketch.

And I did not manually rotate it, it rotated itself once I added the vertical constraint to the line. But it's easy enough to rotate manually - once you have the dimensions added to keep the figure rigid (and before you add the vertical constraint), click and drag on any point to rotate it *close* to the orientation you want. Then add the vertical constraint to take it the rest of the way.

Re: Rotate about the COG

johnsonshiue — Mon, 15 Mar 2021 22:45:49 GMT

Hi! This is an interesting problem to solve. Actually, iLogic may be able to help easily here. First, create a UCS by picking a point in graphics window. Go to Parameters table to find the last 6 newly created model parameters. The first three are X, Y, and Z coordinates for the UCS origin. The other three are the axial rotation.

Here is the simple rule (replace UCS_n_parameter with the actual parameter name). Basically, it captures the COG and populate it to a UCS. The UCS Z axis is the one you are looking for.

centerPt = iProperties.CenterOfGravity
UCS_X_parameter = centerPt.X
UCS_Y_parameter = centerPt.Y
UCS_Z_parameter = centerPt.Z
iLogicVb.UpdateWhenDone = True

Many thanks!

Re: Rotate about the COG

Thegreatrandino — Tue, 16 Mar 2021 16:31:04 GMT

Thank you! Not so sure why I got The geometry being edited is constrained to other geometry. Would you like to those constraints removed? when I rotated the sketch. I guess because there are constraints but message seems unnecessary. IDK

What I learned is the COG point has to be "locked" with dimension to a sketch feature. That make senses.

Thanks again.

Re: Rotate about the COG

Thegreatrandino — Tue, 16 Mar 2021 16:51:07 GMT

This sound intriguing but I don't understand. Can you demonstrate with a screencast

If I go to Parameters, click add numeric and create CenterPt and put = iProperties.CenterOfGravity in the equation I get unable to parse equation

Re: Rotate about the COG

johnsonshiue — Tue, 16 Mar 2021 19:28:58 GMT

Hi! Here you go (see attached part). I used Part2 as an example. Just add a simple iLogic rule. Whenever the part is changed, the COG will be updated and the UCS will be updated accordingly.

Many thanks!