How to extract center of mass dimensions?

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

 

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.

 

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.

 

How about the move/copy body by xyz coordinates?

Respect

 

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.

 

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

 

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

 

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.

 

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

 

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.

 

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!

 

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

 

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

 

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
www.h2omarkdesign.com

 

Ahoy

Well kick me in the pants and call me Eleanor!

'Tis some API black magic ye be needin

Arrrrrrr

 

Ahoy beny!

Well kick me in the pants and call me Eleanor -

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

Arrrrrrr

 

Tanks for putting a smile back on me face.
Arrrrrr

 

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

arrrrr

$0X$