a bug ?

[ASP]

Hi there,
is this a bug or a feature ?
I've created a ASM with a simple SubASM which has 2 mounting-plates and an axis through them.
The axis itself is depending on the distance between the two plates.

Unfortunately the complete SubASM could not be set to be flexible ( I think it was possible in V12 ?)
But I've set it to be flexible before I've created the axis - so in the main ASM "make flexible" is still aktivated
but greyed out.

The strange behavior now is, that in the main ASM the SubASM is not shown correct,
if I edit in place, hitting F5, it looks ok, but back in main ASM it is not anymore ... it is not updated correctly

 

[elzaan1]

Is this what you want ?
Do not delete constraints unnecessarily.
I made that mistake in the start, it is messy when you open the part/assembly file with all the constraints, configs, planes etc in "open" position in the design explorer but rather get past this irritation and unneccisity by closing them and keep constraints and check them by clicking on them and look at their status,- make your decision of deleting / keeping them based on the message received.
This "open" stuff in the design explorer will be highly irritaing especially if you does the "edit part/assem" constantly in large assemblies to get to the parts/sub ass. really fast.

 

[ASP]

no, that ASM has the same behavior as mine,

What i originally want was a flexible SubASM with parts depending on others.
but since V13 (?) it is not possible to make an SubASM flexible which has
dependent parts. (in this example the length of the axis = distance of plates)

So I started this SubASM by setting it to be flexible before any parts are in (without any problem)
But after I added the axis, i've got this strange behavior within the main ASM - because
it is some kind of flexible / but without updating dependent parts - and thats the BUG.

 

[DavidJ]

Sub Assemblies which are flexible allow their contstraints to be ignored when working in the top level assembly - sounds like this is what you are seeing.

The explanation of what 'make flexible' does could be a lot clearer - I only realised when I was working on a moderate sized spreadsheet driven assembly, I though setting 'make flexible' would help, but it just caused chaos when any parameters were updated.

 

[ASP]

David .. again: "make flexible" does NOT override constraints in an SubASM or in any other ASM

anyone else confused about using flexible ASMs ? ... I love this feature and use it very often... should I show some example or make a tutorial ?

... i think i put this to support ...

 

[DavidJ]

I'm not going to argue with you, but I do disagree with you. (If I am mistaken, I require a better explanation of what is happening, and of the wording in the manual).

Maybe someone from Alibre could explain clearly just what 'Make Flexible' is designed to do?

 

[Lew_Merrick]

David .. again: "make flexible" does NOT override constraints in an SubASM or in any other ASM
anyone else confused about using flexible ASMs ? ... I love this feature and use it very often... should I show some example or make a tutorial ?
... i think i put this to support ...

Documentation is always good. The thing that is missing so often these days is a statement as to the philosophy of implementation. Definition of terms is always good as too many of the traditional drafting terms have been turned on their head by CAD programmers/interface designers in recent years. A complementary set of tutorials is always nice.

 

[HaroldL]

Alibre does seem to be a little short sometimes on explanations in its documentation. There are only a couple of entries I could find on "make flexible", one was in an assembly

the other in a table on Locked and Unlocked configurations.

 

[DavidJ]

The yellow highlighted text suggests (but is does not explicitly state) what I hoped 'Make Flexible' meant - i.e. allow parts in sub-assy to move within the limits of the constraints contained in that sub assy, and also obeying any additional constraints added at the top level.

I had awful problems on one complex (for me, though not terribly complex really) assembly with a few sub-assemblies, where using 'make flexible' certainly appeared to override/destroy at least some constraints of the sub assemblies. I'm prepared to accept that I have misinterpreted what happened - I'm also open to the idea that the design intent of the software (whatever that is) may not have been perfectly implemented in all circumstances. I may also have tried to use 'make flexible' in an innappropriate situation - in which case any guidance on when it should and should not be used would be welcome.

As it is I have a concrete example (which unfortuantely I can't post for confidentiality reasons) where make flexible certainly appeared to disrupt the pre-existing constraints, so had to be removed. Until I get a much clearer definition of what it does and doesn't do, I will use this feature with extreme caution.

My problem example was back in v11 or possibley early v12 - so behaviour may even be subtly different now.

I know from my own very limited exposure to software testing in control systems that confirming expected behaviour is generally fairly easy, but eliminating unexpected or unintended behaviours requires much more thorough testing and a lot more effort.

 

[dwc]

I don't know what the documentation says or implies, but I have found that it is impossible to really use motion in any subassembly, with or without make flexible. To get reliable, repeatable behaviour it is necessary to have everything at the top level.
This is experiance from V12.1, seems 2011 is pretty flaky I haven't even tried any motion yet.
Don

 

[DavidJ]

Don,

Yes - this can affect how you might build assemblies if using them in Motion. I would have hoped using Make Flexible for sub assemblies and adding extra constraints at the top level which you can apply Motion elements to ought to be possible.

To date I've always ended up arranging the assembly with all motion related stuff in the top level. Has anyone managed to get examples like ASP's 'make it flexible' tutorial working with Motion?

[EDIT - I imported Christian's example with all the linear actuators from his tutorial, saved locally and set one sub assembly to flexible. I then applied a mate constraint between end faces of one cylinder and the corresponinding end plate in the 'flexible' sub assy. Switched to Motion and was able to add an actuator to that constraint. I had to have several attempts to get the upper/lower limts correct, as Alibre kept putting in values which 'popped out of nowhere'. In the end The motion of the Flexible sub-assy did work as intended (even though as Christian pointed out) the sub assembly is anchored in the main assembly. So it can work, but can be a bit more of a struggle than it should be...]