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Physical properties

Discussion in 'Using Alibre Design' started by beastro, Sep 11, 2020.

  1. beastro

    beastro Senior Member

    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
     
  2. Lew_Merrick

    Lew_Merrick Alibre Super User

    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
     
  3. beastro

    beastro Senior Member

    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
     
  4. dlaery

    dlaery Senior Member

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

    beastro Senior Member

    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.
     
  6. Lew_Merrick

    Lew_Merrick Alibre Super User

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

    dlaery Senior Member

    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.
     
  8. beastro

    beastro Senior Member

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

    dlaery Senior Member

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

    Attached Files:

  10. beastro

    beastro Senior Member

    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.
    upload_2020-9-11_19-34-3.png
     
  11. DavidJ

    DavidJ Alibre Super User Staff Member

    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...
     
    IonSteve likes this.
  12. idslk

    idslk Alibre Super User

    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.

    upload_2020-9-11_21-59-7.png

    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.

    upload_2020-9-11_22-3-44.png

    As ever: Script use on own risk!!!

    Regards
    Stefan
     

    Attached Files:

    IonSteve and NateLiqGrav like this.
  13. NateLiqGrav

    NateLiqGrav Alibre Super User

    I've been working on this in secret.
    upload_2020-9-11_15-33-37.png
     
    IonSteve likes this.
  14. Ralf

    Ralf Alibre Super User

    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.)
    Add-Material.jpg

    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)

    Add-Material-1.jpg

    As you can see, no rocketry is needed, just an existing Alibre feature. :)
     
    Last edited: Sep 11, 2020
    IonSteve likes this.
  15. Lew_Merrick

    Lew_Merrick Alibre Super User

    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/inĀ³ -- and then could not understand why their weight and mass properties were so far away from reality. What mind??? -- Lew
     
  16. idslk

    idslk Alibre Super User

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

    upload_2020-9-11_23-31-59.png

    you get this:
    upload_2020-9-11_23-33-39.png

    which leads to that:

    upload_2020-9-11_23-29-17.png

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

    Regards
    Stefan
     
  17. Ralf

    Ralf Alibre Super User

    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

    Add-Material-2.jpg

    I hope it helps you with your future projects. :)
     
    Last edited: Sep 11, 2020
  18. NateLiqGrav

    NateLiqGrav Alibre Super User

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

    DavidJ Alibre Super User Staff Member

    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.
     
  20. beastro

    beastro Senior Member

    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
     

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