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.

[Cris-Ideas]

Hello again,

This time I have prepared videos and data sets proving that, as I have  stated before:

constrain solver gets solutions that DO NOT meet boundary conditions.

Here are two examples. One for assembly with flexible component and other for flat assembly. According data sets available for download:

http://a360.co/2ht9pNO

http://a360.co/2gF6wgR

Cris

[blandb]

Cris, 

I don't believe I have noticed your issue.

I use flex assy's and they seem to work fine. I have recreated your bolt example and recorded an mp4.

I have tried attaching it, if it doesn't appear, I can email it to you.

[Cris-Ideas]

@blandb

Hi, and thank you for joining.

So what you present is one of many cases that seem to work. What I am showing are cases that do not work. I do that for Autodesk to take a look in to them and maybe finally fix this buggy behaviour.

Case in your video is not failing because you first apply first joint and than make component flexible. This way constrain solver first solves the assembly as flat and do not fail and than only updates position of components in flex sub.

In such circumstances usually constrain solver does not crash (although there are cases it does).

I am sure that if you try to reproduce exactly what I show in my video you will get identical problems as those I show.

this moment you may ask a question: "Why than I should need to make component flexible first and than constrain it if when I do this the opposite way it works fine?"

Well, this example I show is only to show what is not working in an extremely simple assembly that is easy to debug. I have prepared it for this purpose only. Real life assemblies are way more complexed  and very hard to debug. But in real life you often have situation when you need (would like) to use flexible component being one piece of bigger structure. In such case there are many different constrains between many elements that may influence position and shape of flexible component. It is obvious that you cannot than expect to make this component not flexible when you need to apply constrains to other elements, because you need its flexibility to be able to apply proper constrains of those other elements.

So as I have  explained this example with bolt is for simple presentation only and I deliberately apply constrains in such a way so to expose problems than are happening in real life assemblies.

In this thread I also present some examples of other assemblies from my actual design.

Cris.

[Cris-Ideas]

 Hello,

Here I post another example proving that:

constrain solver gets solutions that DO NOT meet boundary conditions.

Please do not try to tell me again it is getting good solution that is "not following my design intent". It is just not getting solution it says it is getting.

It is not my design intent that is failing but constrain solver. Only thing that is not failing is a bug in it.

I hope to get some answer at some point.

As always data set available for download: http://a360.co/2iooCzV

And ideas seeking support: "Fix Flexibility"

Cris.

[Anonymous]

Cris,

Hope all is well, I recreated you assy, and I have everything working correctly, is this what you were hoping to accomplish? Please see attachments below.

[Anonymous]

sorry, I accidentally replied with a different account...please use @blandb instead.......the other is an account that is not used...

[Cris-Ideas]

@blandb

Hi again,

Thanks for another video and effort.

What you show and propose is the most straight forward way of using flexible components.

Sadly it is not working in inventor so well. In my personal opinion it is not working at all.

Problem is that when you try to use flexible components in more complexed assemblies it is only a matter of time (not very long usually) until you are in a situation your assembly is not usable any more because it is destroyed to a point it can not be recovered in other way than by recreating it from scratch.

I have prepared video showing how easy it is to cause constrain solver to bring assembly in to position against constrains defined either inside flexible component or on the level of top level assembly.

This assembly is fairly simple so it is not so spectacular, but exposes bad behaviour.

for more spectacular destroys of assemblies I would advice you to visit this two older threads, there are videos and data sets:

http://forums.autodesk.com/t5/inventor-forum/flexible-nightmare/m-p/5514888/highlight/true#M537216

http://forums.autodesk.com/t5/inventor-forum/would-you-like-to-use-flexible-assemblies/td-p/5940875/...

Cris.

[Cris-Ideas]

There was not much action on this thread for some time.

Now I have something very interesting to share.

Pleas watch this video. (make sure you have sound on)

Cris.

[skylinejeff]

Cris-

You've really pointed out what is most likely a very big clue for Autodesk to start figuring out why flexible assemblies are so wonky.

I hope they take your excellent video of the trolley and find the culprit soon.  We have issues with flexible assemblies as well, and I've pretty much abandoned them in any model with any level of complexity.

[Cris-Ideas]

@skylinejeff

Hi, I could only advice you to submit Support Case via subscription with video and model for flexible assemblies that fail.

Then there is a chance models will go to development and maybe there will be some changes.

Cris.

[johnsonshiue]

Hi Cris and Jeff,

I am sorry to hear that Flexible assembly is not working correctly for you. Regarding the behavior shown in the latest video, have you contacted Product Support and have a defect reported? If not, please go ahead do it. If it was reported earlier, please let me know the defect IDs. I am more than happy to take a look and work with project teams to resolve the issues.

Many thanks!

[Cris-Ideas]

HI Johnson,

It was a while since you last posted in this thread.

in fact I have supplied number of Support Cases lately. Currently last number on my list is # 155 but I already have new in documenting process.

Cases relevant to flexibility and other positional bugs are:

[CaseNo:12531218.] # 102 bug - AI2017 flexible component solve badly

[CaseNo:12531232.] # 103 bug - constrains solved badly for flat assemlby

[CaseNo:12531239.] # 104 bug - flat assemlby solved badly - constrain solver bug

[CaseNo:12342298.] Bug 114 - flat assembley - constrain not possible to apply

[CaseNo:12344625.] bug 118 - inconsistent POS REP for FLEX component

[CaseNo:12503115.] bug 119.4 - Flexibility not working, constrain solver getting bad solutions, design doctor failes to indicate wrong position

[CaseNo:12531250.] # 125 bug - constrain not possible to apply for flat assembly with patterns

[CaseNo:12531275.] # 129 bug - POS REP update bug

[CaseNo:12531361.] # 132 bug - constrain solver and pattern bugs

[CaseNo:12546519.] # 151 bug - POS REP update bug

[CaseNo:12614127.] # 153 bug - DOFs Anlysis failing = Constrains meaningless

[CaseNo:12615337.] # 155 bug - POS REP bug - grounded component flipping

Most of them has been already sent to development for investigation, but I haven't got anything from them yet. Still hoping something will be fixed.

If anyone is interested in what this support cases are about here you can download videos and models.

# 102 - http://a360.co/2j94lPq

# 103 - http://a360.co/2jfCjFT

# 104 - http://a360.co/2j92g5T

# 114 - http://a360.co/2ktxWqO

# 118 - http://a360.co/2ePv16b

# 119.4 - this one is now over 500GB and far to many files so I will skipp

# 125 - http://a360.co/2jfIt9e

# 129 - http://a360.co/2jfFvBn

# 132 - http://a360.co/2iVjhkU

# 151 - http://a360.co/2jiiRW1

# 153 - http://a360.co/2kG12Rl  &  http://a360.co/2kLJen2

# 155 - http://a360.co/2jOd0aT

Cris.

[WHolzwarth]

Cris, I only had a look at # 155.

I can confirm this issue with other samples.

Walter

[Cris-Ideas]

HI Walter,

Could you then create Support Case with those?

"Solution" I was proposed is rather poor. I was only advised to: Un-ground - > constrain -> update all POS REPS -> Ground again

Cris.

[WHolzwarth]

---

Cris-Ideas schrieb:

Could you then create Support Case with those?

---

Done already "behind the lines", Cris

[Cris-Ideas]

This is ridiculous how "so called flexibility" works in Inventor.

This video shows how assembly is torn apart moment it is set flexible, although there are no constrains that would try to force that. Also whole model was rebuild from scratch according to guidelines gave in Autodesk University.

Please see for your self. (As always remember to have your sound on)

And for those who want to try here you have a link for download. http://a360.co/2lxXIqU

And in case anyone is interested I have supplied support case with that: Case 12663107 - # 163 BUG! - Assembly torn apart by constrain solver the moment it is set flexible

Will this nightmare ever end?

Cris.

[johnsonshiue]

Hi Cris,

I am looking at [CaseNo12531218]#102 bug. This is a bug indeed. It looks like the Flex Posrep overriding the ground causes confusion in local solve and global solve. If the component is ungrounded (without using override), the problem does not happen. Something is not working correctly.

I will work with project team to understand this behavior better and see how we can improve it.

Many thanks!

[johnsonshiue]

Hi! For [CaseNo:12531232.] # 103 bug, it also looks like a bug. Work Point1 in Ogranicznik.iam is an assembly workpoint. It is like a component participating in constraint solve. The issue here is that the workpoint seems to satisfy the local constraints but the top level constraint Mate:24 is not honored. Interestingly, if the workpoint is created at the part level in sklajka 150x150.ipt, the problem will go away. The behavior is wrong. I will work with project team to understand the behavior better and see how to improve it.

Many thanks!

[WHolzwarth]

Let's hope for 2019, Johnson.

Looking forward with eager anticipation..

Walter

[WHolzwarth]

Here's another one (Mp4 in Zip)

Walter

Later: Perhaps caused by myself. After re-arranging the cylinder sub-assy error has gone.