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Can I reference Mass Properties in an Expression?

adrian_vlzkzadrian_vlzkz Member Posts: 258 PRO
Could find anything on the help, basically trying to see if I can use "system" values when writing an Expresion for a Variable. (Mass, Volume, Density...)
Adrian V. | Onshape Ambassador
CAD Engineering Manager
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Answers

  • brucebartlettbrucebartlett Member, OS Professional, Mentor, User Group Leader Posts: 2,137 PRO
    I don't think so but this would be and handy
    Engineer ı Product Designer ı Onshape Consulting Partner
    Twitter: @onshapetricks  & @babart1977   
  • Jake_RosenfeldJake_Rosenfeld Moderator, Onshape Employees, Developers Posts: 1,646
    @adrian_velazquez

    It would be pretty easy to make a "measure volume" custom feature which sets a variable to the volume of a selected part.  Density (and hence, mass) are trickier because FeatureScript does not have access to the material assignment of a part.  What is the overall goal here?
    Jake Rosenfeld - Modeling Team
  • adrian_vlzkzadrian_vlzkz Member Posts: 258 PRO
    The goal is to Drive a shape (a couple of dimensions) based on a specified weight.
    Adrian V. | Onshape Ambassador
    CAD Engineering Manager
  • Jake_RosenfeldJake_Rosenfeld Moderator, Onshape Employees, Developers Posts: 1,646
    @adrian_velazquez

    Maybe I misunderstood.  Do you just want to set a variable to "3 m^3" or "10 kg", or do you want to set a variable to the measured volume/mass/density of an existing part? 
    Jake Rosenfeld - Modeling Team
  • adrian_vlzkzadrian_vlzkz Member Posts: 258 PRO
    I want to set a Variable to 1kg then have my dimensions driven by an expression that uses the Volume. Density would be needed in my expression to know my target Volume
    Adrian V. | Onshape Ambassador
    CAD Engineering Manager
  • Jake_RosenfeldJake_Rosenfeld Moderator, Onshape Employees, Developers Posts: 1,646


    This should be possible using an "any" variable
    Jake Rosenfeld - Modeling Team
  • billy2billy2 Member, OS Professional, Mentor, Developers, User Group Leader Posts: 2,014 PRO
    edited February 2019
    Can you pass the context to a variable's function?

    function() { return evVolume(context, {"entities" : qEverything(EntityType.BODY)}); }



    Hoping this will return the volume of all parts at the position it's in the tree.


  • ilya_baranilya_baran Onshape Employees, Developers, HDM Posts: 1,173
    No, we deliberately block usage of context in expressions (because it can lead to some really unintuitive results -- what if the user does an opSomething call in a parameter?) but a custom feature can easily do thiis.
    Ilya Baran \ VP, Architecture and FeatureScript \ Onshape Inc
  • shouldNotBePostingshouldNotBePosting Member Posts: 10 PRO
    Honestly, referring to featurescript from the variable function may not be necessary, I still had to lookup evVolume. If you're at the need level, just write a featurescript, I can do it in 3 lines of code and have greater functionality with featurescript vs. a 1 line function call.

    I'm going to write a featurescript to set these variables. This is all that needs to be done. Adrian's request is still valid. Why aren't these already being set? The benefit with a feature script is that you can ask which parts to include in a volume calculation which is useful. The globals that you set in a partstudio will have to be "all".


  • shouldNotBePostingshouldNotBePosting Member Posts: 10 PRO
    edited February 2019


     
  • ilya_baranilya_baran Onshape Employees, Developers, HDM Posts: 1,173
    @shouldNotBePosting
    Not sure if I understand your question, but mass properties can be expensive to compute -- we should not be doing it without the user asking.
    Ilya Baran \ VP, Architecture and FeatureScript \ Onshape Inc
  • billy2billy2 Member, OS Professional, Mentor, Developers, User Group Leader Posts: 2,014 PRO
    Sorry, I've got too many computers and too many accounts.

    @ilya_baran thanks, I think I have this under control. I'm going to have a featurescript write the volume to a variable using a featurescript.  


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