Inventor - What's the difference between "grounded" and "fully constrained"?

[3D4Play]

When something is fully constrained, isn't it in effect the same as being grounded, because all degrees of freedom are removed?

[SBix26]

Yes and no.  Fully constrained does mean that all degrees of freedom have been removed, but Grounded is not exactly the same.  A grounded component without other constraints can be moved by using the Free Move or Free Rotate tools, or opening the iProperties > Occurence tab and changing actual position information there.

If a constrained component is moved with the Free Move tool, it will snap back to its constrained position whenever constraints are recalculated; a grounded component will stay where you moved it, still grounded.

Does that help?

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Sam B
Inventor Pro 2021.0.1 | Windows 10 Home 1903
LinkedIn

[andrewiv]

Also, a fully constrained component will move when the components it is constrained to move where a grounded component will just stay in the same place.  And if you change the offset value of one of the constraints of a fully constrained component it will move to the new location provided that the change doesn't conflict with any other constraints.

[Frederick_Law]

Ground - Prevent the part from moving.  Part has no relation to other parts.

Constrain - Part doesn't move because other parts prevent it.  If other part move, it will move with it.

Usually one part could be grounded.  Or constrain to origin/major planes.

[3D4Play]

So, if you take the "free move" out of the equation, a grounded component stays where you ground it (ok, free move it to another grounded location), and a fully constrained component stays where you constrain it. Degrees of freedom are either removed (fully constrained) or unavailable (ignored due to grounding).

Therefore, when you apply a single constraint between unconstrained component "A" and a fully constrained component, or between unconstrained component "A" and a grounded component, component "A" still has degrees of freedom, and should still be able to be moved along any of its remaining degrees of freedom, withou having to use the free move command, right?

[SBix26]

Right.  If it's not happening, feel free to post example files and perhaps someone at Autodesk will take a look.

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Sam B
Inventor Pro 2021.0.1 | Windows 10 Home 1903
LinkedIn

[3D4Play]

Thanks! Then, following this principle: creating a pattern using a grounded component is effectively the same as creating it from a fully constrained component - all of the patterned components have their degrees of freedom either removed or ignored, as with the basic principle of the base component. This assumes I don't suppress or make independent any of the patterned components.

Thus, If I free-move the grounded base component, the pattern itself moves (and stays) according to how I reorient the grounded base component. Likewise, the same result if I modify a constraint on a fully constrained base component: the pattern adjusts accordingly. I'm ignoring free-move on a fully constrained base component, because it's just going to snap back to where it was constrained, in that case, and it has no effect on the pattern itself.

[Frederick_Law]

In short yes.

If you don't need the pattern to move with other parts, you can ground it.

If you want them to move when other part move, constrain to the part.

It depends on your design need.

You may find one is better in different situation.

You can always delete the grounded, add constrain.

Or delete constrain, add grounded.

[3D4Play]

Thanks again. If I add a constraint between an unconstrained component "A", and another component that is either a) patterned to a fully constrained base component, b) is fully constrained, or c) grounded, that component "A" still has its other degrees of freedom, and should move around about them until they are removed by adding further constraints to component "A".

This all sounds exactly logical to me!

[johnsonshiue]

Hi Richard,

Please share the files here or send them to me directly (johnson.shiue@autodesk.com). There should be a reason to explain the behavior or it is a bug.

Many thanks!

[tk2B84A]

Im Hijacking this post. If you consider computer power. What is best ground or fully constrained?

I watched a webinar and got the tip to fully constrain all parts to make handling large assemblies easier.

For exampel I often have bolt and shafts that are put on place with constraints. But they can spin around its own axis.

Should I ground them or use a constraint?

[Frederick_Law]

Should not make any different.

Use "Level of Detail" or "View Rep" to hide parts (nuts and bolts) you don't need to see in large assembly.

Shrinkwrap is another tool.

[JDMather]

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@tk2B84A wrote:

For exampel I often have bolt and shafts that are put on place with constraints. But they can spin around its own axis.

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If you use the Insert Constraint (with RDF) you can fully constrain with one constraint.

[johnsonshiue]

Hi! The difference in terms of compute performance should not be much. Certainly when a component is grounded, it has zero DOF, which reduces the number of equations. But, usually the performance issues are due to something else.

I don't believe the two make much difference on performance.

Another thing about the two is the difference between the design intent. Grounded means the component is stationary at the particular location relative to the coordinate system. "Fully constrained", on the other hand, means the component is attached to something and it can move with the constraint participants.

Many thanks!