Calculating Weight

Napper

I am sitting here designing the interiour of a boat and our engineering department is constantly on my back asking "how much all of this will weigh?" So I decided to spend a couple of hours on Google trying to find a plugin with which I can

a) Assign a density to a volume group
b) calculate the weight of an selection of volume groups with density assigned.

So far I haven't found anything - which surprised me.

I read, that Sketchy Physics lets me assign a density to a group, but is there a way to calculate the combined weight of a selection of groups?

TIG

Look for my 'Center of Gravity' [CofG] plugin - its main post is here http://forums.sketchucation.com/viewtopic.php?p=229401#p229401.
You can pick any 'solid' group or component instance and assign a density to it and it returns its volume/weight, CofG marker and the 6 SPs [balanced-suspension-points]. In the thread that comes with it there's also stuff about exporting your CofGs' data to an Excel CSV file etc.... also separate reporter tool is available here http://forums.sketchucation.com/viewtopic.php?p=278046#p278046

Napper

Hi TiG!

I was reading about your tool as well and just tried it out. It's pretty cool! Maybe even a little too cool for me, as it does more things than I want it to do.

It would be awesome to just be able to apply a density to each volume-group without performing any operations. If this attribute would be copied along when copying a group, I could start out with my designs by creating simple material-groups (Stone, Plywood, Hardwood, Marble, whatever) each with a density applied - then use your script to export all volumes + densities to Excel and thereafter calculate the total weight. Something like that.

This way I could design as I please and give my collueges a fairly accurate weight of my construction in Progress whenever they need it.

The silly thing is that I can assign custom attributes to dynamic components out of the box but not for simple groups. Is there a way to accomplish this?

Kind regards,

Napper

mitcorb

There is a plugin that will allow you to name a group. However, I do not know if this makes it some sort of component. I think the whole point of a component is that it gains an identity as a .skp file but is kept in a components folder. The whole point of a group, as you know, is a "temporary" selection set that may also be a logical, rather than random, assemblage of something that would be eligible for component-izing.

Napper

@mitcorb: Thanks for your reply. This is not really about when to use groups/components - I am pretty confident that I understand that concept (Using Sketchup since V5). It's about assigning a group a piece of information (density) that I can use to calculate the weight, e.g. in Excel).

Example: You are drawing a wardrobe. Structure would be pretty basic:

-wardrobe
--plywood side
--plywood side
--plywood top
--plywood bottom
--glas door
--cardboard back

Each of which would be a group (and the wardrobe being either a group or a componant, depending on if you want to reuse it.

Now Plywood has a different density as glas or cardboard. I would not want to make this dependent on the material assigned to it but rather like to assign an attribute "density" that I can manually set for each group. When exporting to CVS I would get the values group-name, density, & volume for each part and hence I could calculate the weight rather quickly.

I think TiGs plugin sort of works that way but it was built for a different purpose so it goes one step further then I need to go.

mitcorb

And I appreciate your intent. I picked up on your mention of group in your last sentence of simple groups. I misunderstood. I am good at that

mptak

I too am interested in this thread and wonder if in fact much of what is necessary is in the pro version. Wasn't the solid modeling a bit more enhanced. For those who are not boat designers, remember back to "are you smarter than a 5th grader" (or forward to parents out there) that density is mass per volume and unit weight is weight per volume (or density multiplied by "little g"). It would seem to me that "volume" must be stored somewhere for each group...perhaps not. Some sort of density number is stored in SP (in the UI screen) though I think all of those models made stable by adding hidden counterweights indicate that it might not be as friendly as it should be. I have noticed that SP doesn't deal with conservation of rotational momentum as it should (think Greg Louganis).

mitcorb

What about Coefficient of Friction, and Aerodynamic Drag? I suppose these would put too much overhead on the program.

Mr.K.1

@mptak said:

It would seem to me that "volume" must be stored somewhere for each group...perhaps not. Some sort of density number is stored in SP (in the UI screen) though I think all of those models made stable by adding hidden counterweights indicate that it might not be as friendly as it should be. I have noticed that SP doesn't deal with conservation of rotational momentum as it should (think Greg Louganis).

Well SU8 calculates solids volume on the fly it seems, not sure it stores the value anywhere.
As for SP it simply takes the bounding box size as volume, so a cone / box / sphere with the same bounding box will have the same volume.
Ofcourse since SP3.1 this can be countered with the optional density setting, and before that you had to add some hidden objects to extend the bounding box.
Momentum is slowly diminished by the default drag/dampening setting, but in SP3.1(and above) you can reset that with setLinearDamping and setAngularDamping

@mitcorb said:

What about Coefficient of Friction, and Aerodynamic Drag? I suppose these would put too much overhead on the program.

For an accurate drag coefficient reading you need quite a complex particle simulator, not to mention a supercomputer to run it, I guess if it's really important you could contact some aeronautical institutes and see if they can help out.

Pretpik

Hi @Napper
did you ever find anything to calculate these 'mixed material' groups?
I am in a similar situation now and my search came up with this thread.