Flexibility not working properly in inventor - BUG that has been there for ever

[Cris-Ideas]

Hi,

I am trying to use flexibility feature but every time I give it a chance it fails me. There is a bug somewhere in inventor that makes it not capable of properly solving assemblies with flexible components.

This time I have run on to this issue with a very simple assembly, had been able to reproduce this buggy behaviour  tens of times, and had made video for you.

After unsuccessfully trying to post this I thought I will make another video for you so you could clearly see what is the difference when assembly is flat.

Here it is.

Here I have uploaded data set for you to play with :  http://a360.co/2fmTsvD

And in case you also think this is not working properly you can support idea to fix this: Fix flexible assemblies !

Cris.

[johnsonshiue]

Hi! Yes, quite a few of PosRep+Flexible issues have been addressed on our internal build targeting the new release. There is a Beta build available to test. Please feel free to sign up Inventor Beta program https://feedback.autodesk.com/welcome/). You can try the latest Beta build on an install-free environment. I just try this particular case and it works fine there.

Many thanks!

[WHolzwarth]

I think, this setup (Flexibility Test) does not move by itself, because the Flexible Subassembly is grounded.

I've added another part as grounded part, and removed the fix from the sub-assy.

Now it's moving well.

New main assembly attached, no changes in other components.

[Cris-Ideas]

Hi,

I need to report to you as I have tied flexibility in AI 2021.

It is after midnight and I am still struggling to produce proper drawings out of my model. Unfortunately this is not an exercise but my real life work. Unfortunately firstly because I need to get it done and secondly because I am not able to shear this due to NAD, so no video this time ;-(.

As for what is not working.

Luckily no critical destruction of the model so far. I see some improvement over previous relies, but still it is not working 100% correct.

This time I am getting unjustified errors from constrain solver when I am using POS REPS, FLEX and LOD. I kind of suspected it will be to much, but this was the easiest way to present my model in all the stages I need.

So initially in POS REPS, when defined, all is fine, but after leaving and activating POS REP again error appears as assembly can not be solved (all of the sudden FLEX component does no longer solve properly, although it should). As a consequence assembly is not being solved any more and it is not possible to get proper representation of the model.

Another thing I noticed is that FLEX just kills inventor when I try to drive some constrain. It takes several hundred times longer to perform the same drive when one of the components is FLEX, comparing to when this component is standard.

And I do not have very complexed model this time. Only thing that is FELX is a rotation of the shackle in a hole. So no complicated kinematic chains.

Overally I have an impression that 2021 may be more stable with FLEX than previous relies but if it works it only do so for simple assembly structure not involving LOD.

Cris.

[Cris-Ideas]

Update after more struggle.

It does not work.

Felx component does produce ridiculous errors and it is not possible to get proper representation of the assembly i POS REPS.

I need to redo entire model and, as usual, DO NOT USE FELX.

Few days wasted.

Perhaps some problems have been addressed but still once that are still there spoil everything.

[Cris-Ideas]

I kind of find out what exactly causes the problem.

If assembly in in the LOD that has FLEX component suppressed all POS REPS having constrains requiring flexibility of this component are immediately broken. Just as if FLEX component when suppressed was no longer FLEX, and constrain solver is not able to solve its constrains. 

If I only need visual representation I could go with DVR instead of LOD, but I also need proper mass and COG for various stages, so either need LOD or many assemblies, each with different elements set (this however is annoying when I change something, as I need to update many files manually instead of having this done automatically).

I have also noticed other bug, also quite old, that still continuous.

So issue is that although given POS REP of the assembly can not be solved, it is not indicated as broken in the browser until I activate it. This leads to very difficult troubleshooting of the model, as communication in  the browser indicated all is fine, when in fact it is not.

Cris.

[nannerdw]

I've completely replaced PosReps with iAssemblies that have excluded constraints and parameter overrides.  It's a more tedious workflow, but it's almost guaranteed to update all of the constraints correctly every time without randomly forgetting to move one or two parts into the new position.  The iAssembly workflow does not rely on flexibility either, since the part positions are stored inside each member file.  The only time I use PosReps anymore is when I'm adding an assembly from a library that can be in multiple positions, but I only need to show it in one that's not going to change.

Sometimes I'll make an iAssembly that has members like "0 deg, 90 deg, 180 deg, 270 deg, Flexible." I make the Flexible option the same way that I'd typically create a Master PosRep, which in this case means excluding the angle constraint instead of suppressing it.  That flexible option would have to be used with caution, though, since it would be susceptible to these constraint glitches.

Just remember to always check that an iAssembly is set to "Edit Factory Scope" before you close it, so you won't start editing it later and accidentally add a bunch of columns to the iAssembly table.  Also, if you make a small change like an iProperty change and the iAssembly member files refuse to regenerate, just open the iAssembly spreadsheet in Excel, save and close it, and that will force the iAssembly factory to recognize that all of the members actually do need to be regenerated.

[johnsonshiue]

Hi Cris,

Many thanks for confirming the improvement in 2021! Indeed, quite a few failed cases you reported have been resolved on 2021. But, I do believe there are still issues. For example, the pattern issue you raised on the other thread is not yet resolved. We don't have a good solution for that.

Regarding LOD, like I mentioned before, it was designed for memory management purpose. For modeling purpose, it is better to keep LOD:Master active so all components are computed using proper geometry (instead of cached geometry from unloaded components).

If you want, please share the files you are working on with me directly johnson.shiue@autodesk.com. Or, you can report an issue with our support staff.

Many thanks!

[Cris-Ideas]

Hi,

Regarding patterning flex components.

As long as you need all components in the pattern to follow the same position/ position change it is actually quite easy.

All you need to do is to place component in another sub assembly and patten it.

Than make this sub assembly flex and you have pattern of flexible components.

As for modelling.

I very often have situation where I have assembly that is being assembled (in real life) and during this assembly process some parts are added before and some are added later. In the mean time structure is subject to changing support condition or movement (rotation) so loads change.

It is important for me to know weight and COG position, as well as to be able to do FEM analysis in stages so I need to suppress some components.

Alternatively I would have to have many assemblies (at least one per stage). So I would end up with many assemblies of the same structure that I would need to update manually every time I change something in the design. (not every change in the design would require to do so, but any change requiring changing constrain set of the assembly would).

So having one assembly for one structure is best for me. But unfortunately this does not work.

[Cris-Ideas]

# 292 bug - Crane

This is how POS REPS and FLEX work in real life.

as you will hear I was even more surprised than expected.

Link for the model:

https://www.dropbox.com/s/799k1fx29hk33be/%23%20292%20bug%20-%20model.zip?dl=0

@johnsonshiue 

Johnson,

You have stated many times that flexibility and POS REPS are getting fixed and that they are usable.

So I challenge you and inventor team to produce evidence using this model. You are free to change it and constrain it anyway you want, only design intent and overall geometry is important.

This model is not complicated in principle so if FLEXIBILITY is in fact working please prove it by making it work.

Please post your videos and model so we can all see and test.

Cris.

[Anonymous]

You have a sick flush constraint between Group_11_1   and  Group_11_23 that was affecting it for me.

[johnsonshiue]

Hi Cris,

Many thanks for sharing the files! Challenge accepted! I cannot guarantee there is no bug. I will take a look and get back to you with my findings.

Thanks agian!

[Cris-Ideas]

@Anonymous 

This groups are components of the crane.

Crane is constrained properly and in very simple way. This flush constrain is fully legitimate and does not cause a problem.

It is recognised as "conflicting" although it does not produce any geometrical conflict. This is just a wrong aswer from inventor solver.

If yo examine the crane assembly you will find out that it is made so in fact crane has ability to move and take any position within range required to solve top level alignment.

So constrains I apply in top  level assembly (lifting scheme) do not require position of the crane that is not allowed by its internal structure. But despite that inventor is not able to properly position the flexibility crane assembly.

Actually after struggling whole day ( @johnsonshiue  extensive waist of time that costs a lot, have in mind that is my real life project I have budget for and limited time to execute.) I have discovered that most likely solver has problems with rotation around vertical axis of the crane if it needs to rotate more than 90 deg to the next position.

So in general constrains defined in any of the components are so so they do not produce geometrical conflicts and it is possible to get proper alignment of parts without any conflicts.

If any conflict appears this is ONLY BECAUSE SOLVER ISSUE.

@johnsonshiue 

I ma really keen to see how Inventor team will assemble this.

As for my solution I needed to bring parts of the crane to the top level. With the same set of constrains there are no issues. (No surprise for me) (That also proves there is no real issue with flush constraint between Group_11_1 and Group_11_23).

What I have also noticed is that this bug with promoting POS REPS  was not fixed 100% and there are still situations when geometry of the component is read from MASTER POS REP instead of selected pos rep.

This is 100% repeatable behaviour. ( this happens when top level POS REP is copied to create new one)

Cris.

[Cris-Ideas]

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I was just accidentality browsing this thread in early pages.

I have found this post from 12-08-2016:

How many updates do you think have been made for this article ?

I checked out of curiosity = NON

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@bob_holland wrote:

@Cris-Ideas

Thank you for bringing this to my attention and we are sorry for your inconvenience.
I have sent this to our development staff for them to resolve in an upcoming release or service pack.

I have created a web page and the investigation have been documented in the article published here:

http://knowledge.autodesk.com/article/Flexibility-not-working-properly-in-Inventor

We will keep the article updated with the findings from the investigation, as they become available. You may look up the article by searching Autodesk Knowledge Network using the Incident Id: 166160 for the status of the investigation any time.

The above webpage should be live tomorrow (Friday) morning PST.

Thank you for your patience while we work to get this resolved.

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[cadman777]

Cris,

I got to this thread from another thread on flexibility/DOF/Constraints.

Sorry, I had to laugh at your 'expressions' in the crane video.

Now (after hearing your 'expressions') I why nobody would come to my office.

Maybe they thought I would 'go off' on them!

Incidentally, I use Inventor 2010, and quit using flexibility back in 2011 b/c it is so bad.

I only use it on occasion when I absolutely need positional representations for showing motion and direction (like with air cylinders). But it ALWAYS works BAD! Besides, to get it to work 'good enough' requires too many 'work-arounds' in the absence of true fixes.

Also, I quit using most of the functions in Inventor 2010 b/c of too many work-arounds with each function.

These work-arounds kill productivity and cause undue use of mental energy.

I want my software to be a TOOL, not a CAREER!

Anyways, now you can see why I have not 'upgraded' since 2010, b/c NOT fixing BUGS is the RULE for Autodesk executives and investors...

[cadman777]

Cris,

I got to this thread from another thread on flexibility/DOF/Constraints.

Sorry, I had to laugh at your 'expressions' in the crane video.

Now (after hearing your 'expressions') I why nobody would come to my office.

Maybe they thought I would 'go off' on them!

Incidentally, I use Inventor 2010, and quit using flexibility back in 2011 b/c it is so bad.

I only use it on occasion when I absolutely need positional representations for showing motion and direction (like with air cylinders). But it ALWAYS works BAD! Besides, to get it to work 'good enough' requires too many 'work-arounds' in the absence of true fixes.

Also, I quit using most of the functions in Inventor 2010 b/c of too many work-arounds with each function.

These work-arounds kill productivity and cause undue use of mental energy.

I want my software to be a TOOL, not a CAREER!

Anyways, now you can see why I have not 'upgraded' since 2010, b/c NOT fixing BUGS is the RULE for Autodesk executives and investors...

[cadman777]

Cris,

I got to this thread from another thread on flexibility/DOF/Constraints.

Sorry, I had to laugh at your 'expressions' in the crane video.

Now (after hearing your 'expressions') I why nobody would come to my office.

Maybe they thought I would 'go off' on them!

Incidentally, I use Inventor 2010, and quit using flexibility back in 2011 b/c it is so bad.

I only use it on occasion when I absolutely need positional representations for showing motion and direction (like with air cylinders). But it ALWAYS works BAD! Besides, to get it to work 'good enough' requires too many 'work-arounds' in the absence of true fixes.

Also, I quit using most of the functions in Inventor 2010 b/c of too many work-arounds with each function.

These work-arounds kill productivity and cause undue use of mental energy.

I want my software to be a TOOL, not a CAREER!

Anyways, now you can see why I have not 'upgraded' since 2010, b/c NOT fixing BUGS is the RULE for Inventor...

[Cris-Ideas]

@cadman777 

I also pretty much quit using flexibility.

I only now and then try to use it, thinking it would be the easiest way to get things  done.

But as obviously as it is it turns out bad idea costing me time. Only what little cheers me up is making videos of it and posting here in this thread to expose how things really are.

As for my self last year was the last year I have purchased Inventor. I am staying with 2021 and will not pay any more.

I have been raising issues important for me since 2012 and still basics are failing.

I do not use practically any of, so advertised, design functions (bolted connections, LOD, frame generator, ....) because, exactly like in your case, they require to much care and produce to much errors.

I have however ONE 100% stable workaround for flexibility, and NO it is not "Do not use it".

Actually as I have proven flexibility does not bring any issues on one particular case: When there are no constrains in flex assembly.

But this is rather not practical way of use, although in some very particular cases it can be used.

Cris.

[Anonymous]

I for one will miss the entertainment value when you finally give up the fight Cris.......so please don't give up the fight, even if the rest of us have! LOL

[WHolzwarth]

Cris, I took a look at the crane's assembly.

What do you want to see with all these extension Posreps? I'm only seeing errors caused by no more existant geometries?

[Cris-Ideas]

@WHolzwarth 

So my goal is to sell this idea to client in a way so I get a contract for the design (this stage it is only a concept)

So I need to prepare nice, easy to understand presentation (comic book) that will help me to present the solution and convince the client this is fast, easy and cost effective.

In order to do that presentation needs to be "self explanatory" to anyone, especially someone who may not necessarily be interested to hear it.

This particular assembly I am using to prepare drawings related with this tower installation to show steps required for the installation. I need those to firstly, put in the concept design and secondly, to produce views I will use in the presentation.

So instead of having 7 individual assemblies for each phase I prefer to have one, as it is much easier to keep up with changes (I make a lot of them during design process).

This is why I need all this POS REPS.

Unfortunately I am not able to shear final result for you to see.

I can however show you document concerning other project (it is in Polish, but I am sure you will get the idea), it is something little different, as more focused on technical aspects rather than presentation, so a little different scope of sketches.

But principle was the same = have single model to produce all the drawings.

Second document is more of a presentation.

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@WHolzwarth wrote:

Cris, I took a look at the crane's assembly.

What do you want to see with all these extension Posreps? I'm only seeing errors caused by no more existant geometries?

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But there is no geometry that is missing. What changes is only constrain values or some get suppressed.

"second edit"

I finally got the question.

So extensios I did to be able to use this crane assembly in different contexts (dependgin on what I want to lift).

Last time for exampel I was using it in an assembly manual fo launching nose when I was preparing lfting schemes for 20t+ steel segments, so the boom needed to be short,

This time I needed long boom, for high lit.

But I am not able to set this boom dynamially extendable (no need) so I use POS REPS to have fixed boom lengths.

Cris.