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How to read mass? [fixed]

Discussion in 'Using Alibre Design' started by sz0k30, Oct 19, 2020.

  1. sz0k30

    sz0k30 Senior Member

    MASS-1.png MASS-2.png

    Trying to read the mass of this asm. It doesn't make sense to me? What is 2.68536....E6 in pounds?
     
  2. HaroldL

    HaroldL Alibre Super User

    That is scientific notation, move the decimal to the right as many places as the number after the "E". In this case 6 places to get 2685369.534 lbm.
     
  3. Hunter

    Hunter Senior Member

    Check your material density, probably too high. Did you change units?
    Edit 2: See my post further below, it's been logged and accepted as a bug.
     
    Last edited: Oct 20, 2020
  4. bigseb

    bigseb Alibre Super User

    Its the centre console for a Star Destroyer... *groan*
     
  5. sz0k30

    sz0k30 Senior Member

    Yeah! That's what I thought. 2.6 million pounds is a bit high. 26 pounds is closer to the real weight. The assembly is made up of steel, wood & plastic pieces. I was pretty sure I went thru all the part files and had the correct materials, default densities and all english units (lbs).

    Looks like I'll have to go thru it all again.
     
  6. simonb65

    simonb65 Alibre Super User

    Just create a BOM table and add a mass column, see which one looks massive!
     
  7. sz0k30

    sz0k30 Senior Member

    Houston, we have a problem!!!

    I just went thru and checked all the individual (16) files. The materials & mass were all correct. I manually added them up & came up with a total weight of 24.7373 lbs. Then Simon, I followed your suggestion and created a BOM table and again the total weight came out to 24.75 lbs. This assembly has 2 sub-assemblies, their weight came out correct. So where does the extra 2.6 million come from?
     
  8. HaroldL

    HaroldL Alibre Super User

    I generally don't have a Mass column for any BOM tables I might use but this issue piqued my interest. So I went thru the assembly and added material to each part. Then I added a Mass column to the BOM table for my assembly. Now back on the drawing there is NO DATA in the Mass column, However, if I add a Weight column then each parts "mass" is listed in the Weight column and the Mass column is asking for Custom Data. What gives with this? o_Oo_O

    Also, like sz0k30, in my assembly the total Mass = 1.443203966E9 lbm but my BOM table in no way totals to that. So where is the extra weight/mass coming from?

    And is there a way to show a total for the weight/mass at the bottom of the table?

    BOM Tbl.png
     
  9. idslk

    idslk Alibre Super User

    Hello colleagues,

    i made a simple assembly from scratch with AW6061 as material from new library:

    upload_2020-10-20_6-20-49.png

    with a simple BOM in summary form:

    upload_2020-10-20_6-22-21.png

    The RefCubeAssembly is "treated as a part". And now the BOM in "standard" format:

    upload_2020-10-20_6-24-22.png

    hm?

    Regards
    Stefan
     

    Attached Files:

    TimoCAD and Hunter like this.
  10. Hunter

    Hunter Senior Member

    Something is seriously wrong here...
    Below cube is 1m^3, density of 1000 kg/m^3, so its mass is 1000 kg (or 1E3kg in E-notation). The surface area is correct, design summary too.
    upload_2020-10-20_8-14-15.png

    If I edit the root assembly, and inspect Physical Properties, I get a mass of 2E9 kg. It should be 2 x 1E3 kg = 2E3 kg. So it is 1E6 times 'heavier' (more mass really) than it should be. Out by a factor of a million. Design summary, volume, surface and CoM is correct. I didn't check mass and inertia moments.
    upload_2020-10-20_8-20-44.png
    I'll submit a ticket, this cannot be.
     
    Last edited: Oct 20, 2020
  11. Hunter

    Hunter Senior Member

    Logged and accepted as a ticket
     
    idslk and simonb65 like this.
  12. Lew_Merrick

    Lew_Merrick Alibre Super User

    It probably means that your Material Properties values in your Parts are improperly set. One group I work with "defaults" to a Density of 1 kg/cm³ -- and then wonders why their "mass" is always wrong! "2.68536....E6" = 2,685,369.534 lbs. -- Lew
     
  13. sz0k30

    sz0k30 Senior Member

    No Lew, the material properties in my part files are correct. They are the default values from the Material Library per the materials I am using. The problem is Alibre. A 26 pound assembly should not weigh 2.6 million pounds. My original post was more an issue of not believing my eyes.
     
    idslk likes this.
  14. sz0k30

    sz0k30 Senior Member

    Here's another good one. This rack weighs 62 million pounds?

    MASS-OR-MESS.png
     
  15. idslk

    idslk Alibre Super User

    Cool,
    it looks like you're a real Heavy Metal Fan :D
    Rgards
    Stefan
     
    IonSteve and JamesMC like this.
  16. ROTTER

    ROTTER Member

    Part 1 = 3,2E-2 kg,
    Part 2 = 3,5E-1 kg
    Part 1+ Part 2 = 3,8E8 kg=380 000 000 kg. This is amazing.
    The parts are step files imported from TraceParts
     

    Attached Files:

  17. JamesMC

    JamesMC Member

    I am having this same issue, was wondering why the trolley I just designed was 12280157.71kg o_O, not the 250kg or thereabouts I was expecting!
     
  18. HaroldL

    HaroldL Alibre Super User

    It'll be interesting what the response from Support will be and if there will be a hot-fix for it now or rolled in to v23.

    Odd that this didn't come up during Beta testing.:confused:
     
  19. sz0k30

    sz0k30 Senior Member

    In going thru some of my other assemblies, I found one that has about 25 different parts, some of which are used multiple times. It appears to have the correct total weight. So checking 3 large assemblies (for me at least), 2 had very incorrect & ridiculous total weights, while one had the correct weight.
     
  20. danwilley

    danwilley Member

    Just to add another data point... I just did a physical property check on one of my assemblies (a steel fabricated weldment) and the weight V22 calculated is the same that was calculated in V21.

    About 147 pounds. Extremely close to the actual prototype's weight. The actual prototype is a little heaver but has several extra pounds of weld that are not accounted for in the model.

    upload_2020-10-21_17-10-6.png
     

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