Physical properties

[beastro]

Hi,

Surely, I am missing something...

I want to calculate the total mass and centre of gravity of some assembly and found that I only get the Alibre only returns the mass of the topmost subassembly in the object tree. Is there a special trick to make it include all items of the assembly?

Using the latest official release (not Beta).

Thanks
Berthold

 

[Lew_Merrick]

I want to calculate the total mass and centre of gravity of some assembly and found that I only get the Alibre only returns the mass of the topmost subassembly in the object tree. Is there a special trick to make it include all items of the assembly?

Hi Berthold -- Yu need to assign Material Properties to each Part making up your Assembly (as well as all SubAssenblies). This can be found under File Properties->Units->Material. If you check in the Resources section of the Forum you will find a rather massive list of Material Properties that I have generated. -- Lew

 

[beastro]

Hi Berthold -- Yu need to assign Material Properties to each Part making up your Assembly (as well as all SubAssenblies). This can be found under File Properties->Units->Material. If you check in the Resources section of the Forum you will find a rather massive list of Material Properties that I have generated. -- Lew

Hi Lew,
Thank you for your quick reply!
I have assigned materials to all single parts that make up the subassemblies. Since the parts are of different materials, I cannot assign a singular material to the subassemblies themselves though.
I'll go through all the parts again piece by piece to see whether there is anything amiss there. Some subassemblies have been created with a previous version of Alibre. Not sure whether that has some impact...

Thanks again!
Berthold

 

[dlaery]

edit in part in a new window and assign the material, then check the assembly for the weight.

 

[beastro]

Reassigned all the materials to all the parts again. Does not return any possible value for mass. As a matter of fact, it does not make any sense to assign a specific material to a subassembly. The subassembly/assembly should just add up the masses and momenti, IMO.

 

[Lew_Merrick]

Since the parts are of different materials, I cannot assign a singular material to the subassemblies themselves though.

Hi Berthold -- Material Property definitions apply only to Parts. Parts make up Assemblies, SubAssemblies, SubSubAssemblies, etc. -- Lew

 

[dlaery]

I use this a lot and it works for me. My assemblies have steel, lead and plastic and it usually come back close. my final weight I am checking is usually for example 1.77 grams or 1/16th oz and when I make the actual part it is within 1% of my projected weight.

 

[beastro]

OK, I'll go through all the parts again, but the results are nowhere even in the ballpark....

 

[dlaery]

maybe you have already done this but here are 3 places that would affect your result.

 

[beastro]

Hi Lew and David,

I found the culprit... a M4 nut that had no assignment. I don't remember having that problem in previous versions. BTW, wouldn't it be practical to be able to assign a mass to a part independent of its material properties? I often have to create placeholder parts that don't represent the exact original, but do the trick for the design of functional parts. It would be practical to assign their real world mass manually. One example is the focuser in the design in question. It has all the properties needed to fit into the design but misses a few details that would be too cumbersome to model and are not necessary for the purpose in question.

 

[DavidJ]

This is one aspect where a script might be helpful - a relatively simple script could read and 'print' the material for each component of the entire assembly.

It would soon become apparent if a part didn't have an assigned material...

 

[idslk]

This is one aspect where a script might be helpful - a relatively simple script could read and 'print' the material for each component of the entire assembly.

taken the ball and have added such a function to the script from This Thread where the basic functions are presented...
I have added a "No Material" with zero density and a check box to choose only printing of the unchanged values.
If use check "Print only", you will get printed output in the console window of AlibreScript.
The part properties will stay unchanged!
You have to use the checkbox for "Change All Parts" in addition to the "Print only" to print all / or only selected parts for choosing what will be printed.



If the script detects a part, which has a zero density, it will print empty lines before and after to help finding this parts easier.



As ever: Script use on own risk!!!

Regards
Stefan

 

[NateLiquidGravity]

I've been working on this in secret.

 

[Ralf]

Hi Berthold,

You can use your BOM. (3D Assembly -> BOM)

Create the BOM -> Insert Column -> Material -> Add >>
(Takes only a few clicks and done in seconds.)


Now you can see the BOM with the additional Column: Material
Empty fields without values -> Materials = You (I) have forgotten to assign the material to your 3D Part(s)



As you can see, no rocketry is needed, just an existing Alibre feature.

 

[Lew_Merrick]

I found the culprit... a M4 nut that had no assignment.

Hi Berthold -- Which is why I maintain fully formed Libraries of all types of Fasteners I use. I had a client who's "default" was to set Parts to 1 lbm/in³ -- and then could not understand why their weight and mass properties were so far away from reality. What mind??? -- Lew

 

[idslk]

Empty fields without values -> Materials = You (I) have forgotten to assign the material to your 3D Part(s)

Maybe it's better to use weight because if you haven't checked that:



you get this:


which leads to that:



or you run the script where you can directly correct the missing material...

Regards
Stefan

 

[Ralf]

Hi Berthold,

The extended BOM version would be to add:
>> Material (To check if the "right" material and was assigned to each 3D Part.)
>> Density (To be sure there is actually a material assigned. Not only the default value 1.)
>> Weight
>> Total Weight



I hope it helps you with your future projects.

 

[NateLiquidGravity]

But with Stefan's script and my upcoming script you change data not just view it.

 

[DavidJ]

Ralf is of course correct that you can do the check without resorting to Script.

If using the BoM approach - you may need to use the 'Summary' option for the BoM, if any sub-assemblies are set 'treat as part in BoM'. Using Summary option will make sure you get a complete list of all components.

 

[beastro]

Hi all,
Sorry for the late reply! Somehow the forum forgot to inform me of all the posts since I last replied...

Fantastic suggestions, Ideas and help! Thank you very much everybody!

I am going to dive into creating scripts shortly for another matter which I just posted on the script forum.

Kind regards