Grounding Constrained Components

Grounding Constrained Components

Anonymous
Not applicable
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13 Replies
Message 1 of 14

Grounding Constrained Components

Anonymous
Not applicable

Can someone please explain to this old man the reasoning behind grounding fully constrained components in an assembly?

Properly or fully constraining grounds the component itself by removing all 6 degrees of freedom, so why the double up?

This causes nothing but extra work and headaches when an edit happens. But I'm seeing this a lot of late and it's driving me batty

Ground the base component, then constrain (properly) to such. When edits happen, you'll get the results you expect or should.

Stop grounding!!!

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13 Replies
Replies (13)
Message 2 of 14

mrB_Young
Advocate
Advocate

I couldn't agree more!

I hate opening up assemblies put together by others only to find all these sick constraints and half of the parts are grounded.

Inventor user since 2009
Vault user since 2010
Message 3 of 14

Frederick_Law
Mentor
Mentor

LOL

A full Master Skeleton will have most parts grounded.

Or "constrain to origin".

 

For non-MS.

Sometime it get messy during design.

A part got grounded because the part it constrained to got removed.

 

Of course sometime the designer need to be grounded.

Message 4 of 14

Gabriel_Watson
Mentor
Mentor

It is indeed funny how this can be misused... but being the devil's advocate for a sec I can think of uses where grounding then constraining makes sense.

For example, if you "Ground and Root" design components that are referencing the same UCS/center axis, you could then use constraints as validation rules (test-drive-development, one should say) against functionality-breaking resizing. All parts are referencing the relative center of a building or product, but if their relative size/location of a wall to a window or another is broken after editing a subcomponent in isolation, Inventor comes barking with the rule.

Message 5 of 14

Anonymous
Not applicable

I have no issue grounding while you may still be in design phase if you are needing to verify something, etc. But once done, unground and constrain or joint accordingly. I'm seeing released datasets with everything grounded and constrained. It seems the grounding is part of the release process. No idea why, everyone I've asked said they didn't know, it's just what they've always done.

 

I'm seeing large assemblies with 100s if not 1000s of components all grounded AND all fully constrained.

Open the file posts a laundry list of blown constraints as well. I've even seen an assembly where it was obvious the designer "eye-balled" the location of a bolt as it would in ISO orientation and grounded it instead of using a constraint. Simply rotating the model and the bolts are floating out in space....but hey, it looks great in Iso.

 

Adaptivity, same deal. It's a great tool during the design process, but once done and the part isn't supposed to change size with the part it was based off (think gaskets), break the adaptivity! Now, don't get me wrong, if the design intent of the adaptative part is to, well....adapt, fine, I'm talking about parts that you don't want to adapt but the designer used adaptivity to cut a few corners during the design process....THAT is where it needs to be turned off.

Message 6 of 14

Frederick_Law
Mentor
Mentor

Adaptive, swearing word in Inventor.

Too many adaptive just for projected sketch.

Then they got check in to Vault.

Then adapted to other assemblies.

Change one part and check out the whole Vault .....

Message 7 of 14

mrB_Young
Advocate
Advocate

OMG! Adaptive sketches .... don't get me started 😠

Inventor user since 2009
Vault user since 2010
Message 8 of 14

johnsonshiue
Community Manager
Community Manager

Hi Jim,

 

This is a little bit like a philosophical debate. Either way should work. From the constraint solver's perspective, grounded component means it has zero DOF so the DOF of the grounded components are removed don't participate in the solve. For ungrounded components, DOFs are available and they need to be solved accordingly. However, there should not be a performance impact, since the solve is usually fairly quick.

The point of grounding components is to ensure they stay put regardless what constraints are changed or what components are moved.

Many thanks!

 



Johnson Shiue (johnson.shiue@autodesk.com)
Software Test Engineer
Message 9 of 14

BDCollett
Advisor
Advisor

@Anonymous wrote:

I have no issue grounding while you may still be in design phase if you are needing to verify something, etc. But once done, unground and constrain or joint accordingly. I'm seeing released datasets with everything grounded and constrained. It seems the grounding is part of the release process. No idea why, everyone I've asked said they didn't know, it's just what they've always done.

 

I'm seeing large assemblies with 100s if not 1000s of components all grounded AND all fully constrained.

Open the file posts a laundry list of blown constraints as well. I've even seen an assembly where it was obvious the designer "eye-balled" the location of a bolt as it would in ISO orientation and grounded it instead of using a constraint. Simply rotating the model and the bolts are floating out in space....but hey, it looks great in Iso.

 

Adaptivity, same deal. It's a great tool during the design process, but once done and the part isn't supposed to change size with the part it was based off (think gaskets), break the adaptivity! Now, don't get me wrong, if the design intent of the adaptative part is to, well....adapt, fine, I'm talking about parts that you don't want to adapt but the designer used adaptivity to cut a few corners during the design process....THAT is where it needs to be turned off.


Sounds like the common issue of no standards that are set for the designers and no one making sure designs meet the standards.

Not exactly an isolated issue but a frustrating one for those who have to deal with the models.

Message 10 of 14

Gabriel_Watson
Mentor
Mentor

Another possible fringe case for grounding constrained components is if you had flexible assemblies and just wanted to save time instead of opening constraints one by one to lock their flexibility at a specific value. Then grounding multiple components at once would be a quicker way to temporarily have things made fixed for just a while.
Maybe yet another case would be having free/loose components with a contact solver on, for example, a soup bowl of moving parts, and you just wanted to stir and reconfigure them freely without constraint until you arrive at a point you decide to freeze by using ground, to then take presentation shots or other things..

Message 11 of 14

Frederick_Law
Mentor
Mentor

Ground it to get Pos Rep you want.

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Message 12 of 14

Anonymous
Not applicable

@johnsonshiue wrote:

 

The point of grounding components is to ensure they stay put regardless what constraints are changed or what components are moved.

Many thanks!

 


@johnsonshiue Agreed! I'm big on design intent, if the intent is that a component should not adjust, then constrain it as such, or ground it. The option of placing and grounding the first component in an assembly is one I always have checked. This is just an example where grounding is good practice. But yes, if the design intent is for a component not to move during edits, set it as such.

 

But I'm referring to users doing a blanket grounding. Grounding EVERY component as well as having them constrained. There simply isn't a reason for this practice. When edits do happen, the user is forced to unground everything, adjust/constrain, then reground everything again.....why?

 

I had one user claim they did it so items wouldn't "shift" by accident. If are constrained properly, they won't.

Honestly, I think it's due to a lot of users don't understand nor like the constraint process, especially when it comes to editing and they get a ton of errors during the process. I personally know a few users that when opening a file and they saw all the constraint errors, they were overwhelmed. Once I explained and showed them that correcting one blown constraint error can actually clear a slew of others, they were a bit relieved. But I still think users panic or get frustrated and since they can easily ignore these until it gets to be too much, they simply kick the can down the road, hoping the next guy will fix it.

 

This is where the Angry Elf gets angry, fix your "bleeping" files!

Message 13 of 14

Frederick_Law
Mentor
Mentor

Do need a company "standard" for constrains.

Logical constrains maybe not be most efficient or flexible to changes.

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Message 14 of 14

torbjorn_heglum1
Collaborator
Collaborator

I am another old man who cannot see any reason to both ground and constrain.

 

But as as a user of the master modelling techniques - especially for weldments, I do ground a lot of components in assemblies, since most components share a common coordinate system. It is quick, correct and the time needed for constraint solving is next to nothing. 

 

After we started with master modelling and grounded parts instead of bottom up and constrained parts we have reduced the errors in assemblies significantly and the opening / rebuilding of larger assemblies are much quicker. A complete product here would typically be 10k-30k instances, and I believe that reduced constraint solving might be a significant contribution. 

 

But ground AND constrain - no don't understand.

 

Torbjørn