[Plugin] Center of Gravity

TIG

Are you sure all of the CofGs are in the same 'entities' context.
If some are inside a group then they can't be combined with the others?

If you run it with the Ruby Console open are there any error messages?

Can you post [or PM to me] the file containing the apparently problematical CofGs...

Phono

Hi TIG,
I sent you a PM some time ago. Did you have a chance to have a look at it?
Thanks
JM

TIG

Work on a copy.
Delete all unneeded things - like text and dims.
Purge the model.

I see you have many nested parts, which will stop the object being solid ! Even if they themselves are all solids [but some are not!],,,

Explode the sub components / nested groups...
If the result is not a solid, then work on it until it is.
There are tools to help identify the issues causing non-solidity...

Now find the CofG of the now solid parts.

Combine then as desired...

TIG

There's a new future-proofed update.
http://sketchucation.com/forums/viewtopic.php?p=229401#p229401

TIG

Here's an update with a fix for the FR lingvo file to make it v2014 compatible...
http://sketchucation.com/pluginstore?pln=CofG

Nemesis

Hello, TIG.

At first I want to say thanks for such great plugin. I hope some day SketchUP will be powerful engineering tool as SolidWorks .

I have a small suggestion, when you working with a few components it's not a problem to define CoG of each and then compose them. But when there are lots of components it's quite difficult to make compose for all of them and do not miss some parts. Here an example of heavy model with cloud of CoG points:

Maybe there is a way to make it automatic for bunch of parts, like this:
Step 1. Select range of components/groups;
Step 2. Define CoG of each and then automatic add composite CoG.

Hope I described idea well enough .

TIG

You can do that already.
It's part of the toolset.
Obviously to tidy up later you'll need to put the individual CofG on their own OFF layer.
See th usage in the PluginStore 'Overview' for making 'Composites'...
sketchucation.com/pluginstore?pln=CofG

Nemesis

@tig said:

You can do that already.
It's part of the toolset.
Obviously to tidy up later you'll need to put the individual CofG on their own OFF layer.
See th usage in the PluginStore 'Overview' for making 'Composites'...
sketchucation.com/pluginstore?pln=CofG

Sorry for my English, I described idea not well enough. As for now, when you determine CoG of complex unit which consists of many parts, you need to define CoG of each part and then compose them. It's working ok, if there are not many parts.

My suggestion is to make possible such workflow:
Select all parts of a complex unit and define composite CoG (of complex unit) at once.

In my example there was over 30+ parts. And it was quite hard to define composite CoG.

TIG

But how would you determine the individual part's material and density/weight ?
You need the composite of several CofGs to do that - since a very heavy part will change the CofG in the combined assembly.
If all of the parts use the same material, then you just need to make a single 'group' of all of them, and then create one CofG of that one object. That way you can 'group' parts with the same material, get their containers' CofGs, and then combine those into a 'Combined CofG' - properly reflecting the weight-distribution...

Nemesis

@tig said:

But how would you determine the individual part's material and density/weight ?
You need the composite of several CofGs to do that - since a very heavy part will change the CofG in the combined assembly.

Yeah, now I understand.

@unknownuser said:

If all of the parts use the same material, then you just need to make a single 'group' of all of them, and then create one CofG of that one object. That way you can 'group' parts with the same material, get their containers' CofGs, and then combine those into a 'Combined CofG' - properly reflecting the weight-distribution...

Just tried it, and it worked like a charm. Thank you.

One more question about accuracy. Bigger value means more accuracy or vice versa?

TIG

The default accuracy of 1.0 - which is sufficient for most analyzed forms.
It means the form is sampled in 1/100 == 100+2 steps.
A higher number means fewer steps, and an even smaller number means even more steps.
The number of steps affects the time taken to process the form - a bigger number == less time.
If your form is a solid or quite a simple them the number is of little relevance as the reported CofG weight is unlikely to vary.
If the form is more complex, then a higher number gives fewer steps [say 50 = 50/100 == 2+2 steps], so the reported weight may well be less than the one from the smaller value [say 1/100 == 100+2 steps].
But the chances are that 1.0 will be fine almost every time...

Nemesis

I made a test with my base frame. All parts are solids, with density 7800 kg/m3. Accuracy for both tests is = 1.

For the first one, I've determined CoG for each part separatly and then compose them. Results are looking true.

For the second I've merged all parts in a group and determined CoG, the result is to much high.

Where is my mistake?

Here is the test model:
TestPart

TIG

When you say 'merged', do you mean that you have exploded the various parts into a single container and then ensured that the container is now a 'solid' ?

Nemesis

@tig said:

When you say 'merged', do you mean that you have exploded the various parts into a single container and then ensured that the container is now a 'solid' ?

Under "merged" I meant - group all separate solids in one group, that was my mistake. Now, I made one solid from all parts and CoGs are now almost identical in both cases (separate solids and one big solid). Thank you for your patience.

sketchartist023

Can you tell me what the accuracy % option does? I set to 100 and its quicker but sees less weight and at 1% takes forever but sees more weight. What should that be set at nominally for the most accurate readings? Thank you!!! Very great plugin, TIG

TIG

The 'accuracy' setting affects the result... as you have found.
For simple forms the 'accuracy' of the results will not improve beyond a certain point, no matter what the settings are...
But otherwise the more 'iterations' the tool does the nearer the result is to being 'true'.
If you choose a 'more accurate' value, then the 'weight' might become more accurate, and the CofG might adjust very slightly.
If you have the time... then more iterations gives the most accurate results...
BUT sometimes the differences are so small it's not worth the delay...
It's up to you - your model - your time...

sketchartist023

@tig said:

The 'accuracy' setting affects the result... as you have found.
For simple forms the 'accuracy' of the results will not improve beyond a certain point, no matter what the settings are...
But otherwise the more 'iterations' the tool does the nearer the result is to being 'true'.
If you choose a 'more accurate' value, then the 'weight' might become more accurate, and the CofG might adjust very slightly.
If you have the time... then more iterations gives the most accurate results...
BUT sometimes the differences are so small it's not worth the delay...
It's up to you - your model - your time...

Thanks I found that using an accuracy of 5% works quite well with realtime weight on my end using the correct density I found on the internet for the material I use. Works a charm! Helps with configuring shipping information BEFORE having to go to Fedex etc and create real products beforehand so it reduces capital costs for me Thanks so much again. I have been within 5lbs accuracy with actual shipping items that I modeled. Just an update

pazzamnik

Hey Tig,

Thanks for the CofG plugin. It has been working quite well, but have one small easy, which I think is easy to overcome. I have drawn an aluminum extrusion and set the aluminum density. The size of the extrusion is 1m in length, so I can know my run length cost/per linear meter.

Whether I extend the extrusion 1m to 20m in length, CofG always comes back and gives me the same weight? Yet if I copy the meter long extrusion, put a couple bends on it, and run CofG, it gives me a new and hopefully correct weight.

Wondering if there might b an issue with my group that is causing an issue?

Thanks.

Dave R

What method are you using to extend the extrusion? If you are just scaling the group or component, you aren't updating its definition. If you open the group/component for editing and then modify its length, the definition gets changed and the plugin should give you the results you are looking for.

jojo9

Great plugin! its possible to add some toolbar buttons? i tried but had no luck.

#--------- menu -----------------------------
unless file_loaded?(File.basename(__FILE__))
   txt0="C of G..."
   txt1="Find C of G"
   txt2="Composite C of G"
   dir=File.dirname(__FILE__)+"/TIGtools"
   toolname="CofGravity"
   locale=Sketchup.get_locale.upcase
   path=dir+"/"+toolname+locale+".lingvo"
   if File.exist?(path)
     txt0=deBabelizer(txt0,path)
     txt1=deBabelizer(txt1,path)
     txt2=deBabelizer(txt2,path)
   end#if
   submenu=UI.menu("Plugins").add_submenu(txt0)
   submenu.add_item(txt1){CofGravity.new(1)}
   submenu.add_item(txt2){CofGravity.new(2)}
   
=begin   
  #plus
 	tb= UI.toolbar "Konstruktion"
 	
	cmd = UI;;Command.new(txt1) {CofGravity.calculate}
	cmd.small_icon = "../Images/Center_component_lg.png"
	cmd.tooltip = "Teilmassen Zentrum"
	tb.add_item(cmd)
	
	cmd1 = UI;;Command.new(txt2) {CofGravity.composite}
	cmd1.small_icon = "../Images/Center_component_lg_sum.png"
	cmd1.tooltip = "Hauptmassen Zentrum"
	tb.add_item(cmd1)   
=end  
end#if
file_loaded(File.basename(__FILE__))
#---------------------------------

sidenote. unable to format my text as code. I get a weird looking format table (please see attachment)