Define a point mass 2

[KelleyB]

I'm a Pro/E user who was just thrown into the fire here with SW2003. Hopefully someone can lend me a hand as I struggle to learn this new tool.

I need to define a point mass within a model(part). This point mass would be used to represent the CG of a rudimentary model.

I have read through many of these posts and it seems as though I may need to learn some Visual Basic coding before attempting this. Is this true or is there another way?

FAQ #559-356 looks like it may answer my question, but I don't know much about this API.

http://www.eng-tips.com/faqs.cfm?spid=559&sfid=356

Any suggestions or comments?

Thanks

 

[SBaugh]

That FAQ is a macro. You might try reading up on macro's then copy and past that code in there. Then you can run that macro. I haven't tried using it so I can't be for sure if it works, but I know that its a macro.

Regards,

Scott Baugh, CSWP
3DVision Technologies

http://www.3dvisiontech.com

http://www.scottjbaugh.com

faq731-376
When in doubt, always check the help

 

[KelleyB]

Thanks for the input.

Looks like that macro retrieves the current mass properties and places a point at the current CG of the model. Moving the point does not affect the mass properties (so it seems).

I would like to know if it is possible to give the model empty mass properties, then configure a simulated point mass within the model wherever I choose.

 

[LoveAeris]

KelleyB,

This is a step by step instruction.

1. Tools>Macro>Record and Tools>Macro>Stop
2. You get a dialog box and you name it and save it. The place could be anywhere for now. Just remember where.
3. Tool>Macro>Edit
4. You get VB program comes up . Don't panic and all you have to do is delete all lines and copy&paste all lines from FAQ.
5. Save the script. You can close VB window.
6. Go back to SW and Tool>Macro>Run and select the one you edited.


I tried the macro and it leaves a sketch and a new one is created after adding Extrude and run again.

You assign the macro to an icon in your tool bar, if you want.

 

[ShaggyPE]

I don't believe we are answering KellyB's question. I tend to believe that we are unable to solve this within a single part. I attempted to use two bodies in a part and assign the minimum density 3.2 something x10^-12 and create a small sphere as a seperate body and change the density of that. I was unable to set the second body to a different density.

This same thought pattern could be followed using an assembly. Create your actual part and assign it a nominal density. Then create your microsphere and assign it an astronimical density. Within the assy mate this "massive" sphere with distance mates to locate it exactly where you want it.

This solution is lame. There should be a real way to assign a point mass, but I don't believe there is currently.

-Dustin Biber

 

[ShaggyPE]

Unless there is a way using VB or API to trick the mass properties calc. I however am unfamiliar with these aspects of SW.

 

[TheTick]

To simulate a point mass, perhaps you could place a lump of solid geometry such as a sphere or cube of appropriate volume and density centered on the CG. If you use a rectangular prism, you can also approximate moments of inertia in different directions to a certain extent.

If desired, you can hide (not suppress) the solid body after it is created.

SW doesn't really have a way to just "plunk in" a mass on a point.

If the ladies don't find you handsome, they should at least find you handy.

 

[KelleyB]

Thank you. That's what I was looking for.

Originally I was using Dustin's simple approach, but thought there might be a more efficient method.

I appreciate the explanations from everyone. Maybe this could be a feature to add for future versions.

Anyone, please feel free to offer more on this subject if you know something we don't.

 

[JNR]

1. A solid part is a single part, whether it has multi bodies or not. Thus obviously only one density value is allowed (since we don't have variable density).

2. What is your real purpose for a "mass point"? Do you really want somthing with no moment of inertia? The mass props should give all the analytical stuff you need automatically.

3. We sometimes use a calculated "average" density to get the total weight right for things like PCB assembly models where there is a fairly even distribution of components, etc.

4. If all you want is a point to indicate the cg you can just make a 3D sketch using the cg coordinate given by the mass props. Of course it is manual and has to be update by hand.

It has been a while since I used wireframe/surface systems that used mass points with properties to store the data because it was not an automatic (solid model) calculation. So I have fogotten any significant advantages the mass point might have.



3/4 of all the Spam produced goes to Hawaii - shame that's not true of SPAM also.......

 

[KelleyB]

Thanks for the help, but maybe the answer may already apparent (see posts from TheTick and Shaggy18VW).

I'm really not looking to "retrieve" the CG, weight, or any other mass properties of a part. Yes, I am concerned with setting the weight of the part (of course, average density would work), but it goes deeper than that.

Example:

Let's say that I'm modeling an entire communications system that will be mounted on the end of a pole 10 feet above ground. This communications package may contain cameras, sensors, datalinks, or anything else you can think of. Obviously, there are some CG issuses that I need to worry about, but I'm not going to spend time modeling the entire assembly for one vendor's camera or sensor. This would involve modeling separate aluminum casing, glass lenses, and plastic pieces, not to mention all the electrical compontents inside.

Instead, I'd like to create a simple "part" representation of the component that specifies total mass and CG location (Assume this information is stated by the vendor). This would allow me to configure components on the pole to ensure proper CG alignment of the entire package, avoiding any faiulures that may occur from improper loading.

 

[JNR]

Ah yes, makes perfect sense now. I agree, you could make a (very)thin shelled outline of the equipment for interface/clearance purposes, etc. and have a small heavy square block inside (multi-body part?) to fix the cg and calc. its density to give the mass you need. Note I suggest a square block, not a sphere. If you use a unit size block, it would be very easy to calculate the density required in one simple step (in your head even).

3/4 of all the Spam produced goes to Hawaii - shame that's not true of SPAM also.......