# How to extract center of mass dimensions?

• posted

If I have a part and then check the mass properties I get a 3D coordinate for the center of mass, how do I extract this info and move the part so that the center of mass is at the origin? Basically How do I extract the x,y,z info from the mass properties and input this into an equation or a design table to drive the move dimensions?

I was looking at the CSWP exam examples and see that on one of the test parts it asks "the part origin should be at the parts center of mass" so how would you approach this? I would assume since it is a revolved part you only need to know the axis of rotation (given it is symmetrical) and then establish the center of mass height of the sketch to do this but...

Ben

• posted

The only way I have seen this accomplished, is to create and add a macro feature that reads the value then places it into a constant. Then you can use this constant in an equation.

• posted

I think you're digging too deep.

If it's a revolved section, start with the centerline through the origin. Constrain your sketch such that the entire sketch can be moved up or down by a single dimension while the rest of the sketch keeps its size and shape. Make your revolve, check your C-G, then adjust the controlling dimension accordingly.

• posted

How about the move/copy body by xyz coordinates?

Respect

• posted

One additional thought here, if you are dealing with a symetrical part, then why not just sketch the profile so the CG and the origin are already lined up?

Just a thought.

• posted

Great idea but....I dont know the C of G location so then how do I get the C of G from the sketch? Next is I add some extrusions to the top of the revolved part so the C of G changes.

Ben

• posted

This would work but... if the size of the object changes ie the height of the rotational element (which is part of the test) then the location of the C of G would be incorrect if not changed manually. I would like it to update automatically as the part is changed and put the parametics to use.

I am sure I am reading in to this too much and from the testing grading form I have seen it is a non issue but I am personally curious on if and how this could be done.

Ben

• posted

It can be done with a macro feature. For an example of a macro feature see,

, select "macro feature". Search google for cog macro.

• posted

How many times are you going to do this through the course of a half-day test? Doesn't really seem macro-worthy to me.

Another option is to crack open Machinery's Handbook and look at cross-section shape properties. It may help to be familiar with location of CG for common shapes.

You could write a macro peature to perform this task. Personally, I am not a fan of macro features in their current state. The macro must exist outside of the part file. If tha macro could be embedded in the part file, that would be cool.

• posted

You have a good point on the macro but if you have a design table or a formula driven dimension then it is a part of the part and updates as an imbeded function

Any how I know how to calculate the CG this is a non issue. However to get the cg from the cross section may not be an option as even though it is symetrical it may have varying cross sections, again you could calcutate this out but that is why I bought a computer, to have it calcutate these things for me.

Ben

• posted

I am not sure this is the way to go. As I have said in other posts you do not need a macro you can have a formula drive the dimension, you can also call up other features informtation to drive this dimenstion so what is the call for the x, y, z from the origin for the cg from the mass properties so I can drive a dimension this way? or use a design table?

I am not sure where everyone thinks I need a macro came from? I do not want a macro I want a design table driven dimension or a formula driven dimension.

All I want is the "\$color" type call or 'd1@extrude1" type call that brings up the x,y,z dimensions for the cg that you see when you hit the mass properties button. I will do the rest.

• posted

Ahoy Beny!

What ye does is place a 3d sketch point down with said CG coordinates. Activate ye move/copy bodies tool. Place the bloomin triad on t' aformentioned 3d point. and enter the necissary xyz delta coordinates like a ture seadog would.

Back to work Landlubbers!

• posted

arrrrggg. ye forgets that yer idea is riddled with 'oles. She be eh good one but she is not parametric, i.e. driven by a function on a rebuild... I do not want, ner care fer inputing data over and over as a part develops and changes in shape as the concept develops and changes each time.

But ye be sure twas a exellent ideam just not the one i am lookin fer.

Ben

• posted

Please excuse my ignorance, but isn't that similar to putting the cart before the horse?

• posted

Ah nevermind. this seems to be beating a dead horse. I wanted to be able to have the c of g and the origin at the same point on a part. now as a part devlops it will change. I am unlike most, I guess, and I make changes to parts as I develop a assembly and rarely if ever get the part right the first try

So that being said the c of g changes and I also do not want to each time this part changes (which can be multiple times) have to hit the rebuild, hit the mass properties button, have to write out the x,y,z coordinates, have to go back into the sketch and move the sketch to the cooridinates, or alternately have to go to the move body and change the move distances and then hit rebuild once again.

Or redraw the sketch or change the model and have it, now hold on this is a hard one for people to grasp, pause and think about the next statement, automatically move the c of g and the origin to the same point, key word here is automatically. instead of the whole rigamorole of updateing, changing, getting info, writing it down, changing sketches, and rebuiilding again, bla bla bla

therefore this c of g is in the cart that is behind the horse. I also will now get the usual argument from someone stating "I would never have to do that or need that info therefore, you must not need it either. why would someone ask such a silly question?" instead of picking up the gauntlet that has been tossed and trying to challenge it we will resort to silly blurbs that put one on the map to be heard, but as usual add very little to the solution.... Gahhhhh!!!!!!!!!!!!!

I work on aircraft perdominately and c of g is of the upmost imprtance on parts assemblies etc etc. it helps to have things in balance, which is why I want a parts c of g and finally do calculations based on these c of g's to get approvals by the local transportation athorieties.

I am tired of trying to explain and I am getting snarky and turning into a person I do not like ,an ass so I will give up on this. I encourage the rest of you to do the same. I appologize for snapping, no ignorance on your part just a apparently stupid question on my part.

Ben

• posted

Ben, I can easily understand why you would like to have this function in a macro. I personally wouldn't need it often, but I have had some use for such as that once upon a time. Others may poo-poo the need, but I just don't think they "get it". I wish I had an answer for you. If you find one, please let us know about it.

Mark 'Sporky' Stapleton Watermark Design, LLC

• posted

Ahoy

Well kick me in the pants and call me Eleanor!

'Tis some API black magic ye be needin

Arrrrrrr

• posted

Ahoy beny!

Well kick me in the pants and call me Eleanor -

"Tis some API black magic ye be needin...

Arrrrrrr

• posted

Tanks for putting a smile back on me face. Arrrrrr

• posted

Aye beny. Life is but a smile on the face and terror in the heart...

arrrrr

\$0X\$

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