topic Re: Flat assembly destroyed, constrains flipped - FIX IT challenge in Inventor Forum

Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Thu, 02 Aug 2018 22:47:32 GMT

Welcome.

I had dug up one of the old unsolved cases, and inspired by latest discussion decided to post it as a challenge for all who are willing to try their constraining techniques with this task.

It is flat assembly, that uses no flexibility and no range constrains. But there are no restrictions on how it should be constrained. All inventor valid technical solutions are accepted.

Assembly is now destroyed by the constrain solver. It was originally brought to this state by constrain solver, as user would not be able to do that. I had not been able to fix it in any other way than removing most of the components and building from scratch. But even than it was not stable.

Design intent is simple - This is to be constrained in the way so it's DOFs are equivalent to real life construction. (This was actually build and used on construction site).

Criteria for the challenge:

- it must be stable,

- it must be draggable within its proper envelope. So it was clear that constrains positioning upper beams can be applied separately from structure's internal constrain set,

- data sets of the solutions must be provided,

- video comment most welcome.

data set for download: https://autode.sk/2n8PsRc

Cris

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Xun.Zhang — Fri, 03 Aug 2018 07:42:58 GMT

Hi Cris,

Today, Played with your data and deleted all constraints and then re-create every constraints from scratch in Inventor 2019, so far, everything goes well and the constrains flipped is not happen any more and the result is much more stable and robust.

Please check out the data and switch the pos-rep to view the result.

Notes, the Max position you've provide is not valid since the arm length is not enough.

Min

Max

Drag-able video -

https://autode.sk/2n7mq4g

Note, the entire constraint chain contains >6 DOFs, so it's better to disable some of them when drag.

By the way, please try with flexible for big/small props which should work correctly as well in Inventor 2019.

Hope it helps!

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 07:54:35 GMT

@Xun.Zhang

Hi,

Thanks for the effort.

However in your video few issues are clearly visible and they would require additional work to be done.

Please see how most right prop gets of allowable range. Also during dragging upper beams go out of boundary as props seem to have no limits. (witch is clearly out of real life solution).

If you can provide solution with flexible components you are most welcome. I have many issues with flexibility, and as far as I know there is no significant change in 2019.

For the time being I am unfortunately not able to install 2019 as run out of disk space. Will work on that.

In the meantime you can figure out the limits.

If you are interested in other challenging issues you can visit this threads, where you can find many examples.

flexible nightmare

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

Cris.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Xun.Zhang — Fri, 03 Aug 2018 08:13:55 GMT

Hmm...

I don't fill the limits with the range in. I don't see any problem in the video, do you mean the conflitions? the reason for the conflitions happen exactly because of the picture you show me is not match the model.

Limits is an addition condition for sure, but it should not affect the result. Hope you can understand that limits is not the major factor which cause the constraint chain problem.

Flexible stability is more robust since the possible solution with axial direction involved and the result is become unique for entire constrain chain.

You can image that if the system constrain chain is unique, the result is more robust. Flexible is a way to compute sub-constraint chain in the top, so you have to make sure each level constraint chain is unique before leverage flexible approching.

Thanks!

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 08:24:48 GMT

@Xun.Zhang

I suggest to move general flexibility related discussion to this thread. Flexibility not working properly in inventor - BUG that has been there for ever and this one only use for this particular assembly related problems basing on examples.

I am happy to discuss flexibility so I encourage you to join the other thread.

As for solution:

Originally props have been constrained to allow only move within safe limit of the thread to work. So this was in the design intent from the beginning.

If you look in the constrains defined for each prop in my assembly (if you delete everything except single prop it will work) if you than turn all constrains for the prop you should be able to see the limits.

I am uninstalling some staff to free some space to install 2019 just to be able to play with this dataset, as I will be still using 2017 for work.

Cris.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Xun.Zhang — Fri, 03 Aug 2018 08:58:11 GMT

Hello @Cris-Ideas,

Sure, welcome to Inventor 2019!

Thanks!

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

jletcher — Fri, 03 Aug 2018 11:42:38 GMT

Your challenge is rig and can never work because of your unreasonable request.

@Cris-IdeasWrote:

Design intent is simple - This is to be constrained in the way so it's DOFs are equivalent to real life construction. (This was actually build and used on construction site).

Criteria for the challenge:

- it must be stable,

- it must be draggable within its proper envelope. So it was clear that constrains positioning upper beams can be applied separately from structure's internal constrain set,

1) In real life construction you cannot drag the beams to work, this is turn buckle adjustment in real life and that is what you would have to do in Inventor to see it work.

2) If the location of the "Motion Envelope" is correct with these numbers your design has failed already and cannot fit into the window you are asking.

If that is the correct location the "rama 1" is not design correctly from the start as you can see in the photo below.

I can make this work like it was real life by turning the buckles but it would never fit your Motion Envelope.

As you can see in @Xun.Zhang photos the "Motion" Envelope has moved, I believe this would not meet your criteria because you had a location for the "Motion Envelope".

This would be easy to do.

Just a suggestion if you want to animate anything in Inventor I have found that offset constraints makes it unstable, and mating to assembly plains not grounding the 1st part and constraining from it also makes animation unstable. Not say you can't just more stable if you don't.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 11:59:30 GMT

@jletcher

James just try, or leave this thread alone please.

Cris.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 12:25:14 GMT

@Xun.Zhang

Have installed 2019.

So you can upload data set or link for download when ready to test.

Cris.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

jletcher — Fri, 03 Aug 2018 12:34:22 GMT

Nothing to try, you rigged it.

I just don't want people wasting time on a rigged challenge.

You claim @Xun.Zhang did not stay in your "Motion Envelope" I pointed out you can never be in that "Motion Envelope" because of design flaws from the start.

But he clearly shown you he got it to work.

Also real life you cannot drag the beams and you asked for real life construction.

Have a good day.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Xun.Zhang — Fri, 03 Aug 2018 12:34:39 GMT

Hello @Cris-Ideas,

See my first post, the data was enclosed.

Thanks!

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 13:29:09 GMT

Quick video regarding props and limits.

Cris.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 13:43:34 GMT

@Xun.Zhang

I have downloaded your data set.

Here is a comment

Cris.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Xun.Zhang — Fri, 03 Aug 2018 14:16:28 GMT

Hello Cris,

Thank you so much for the comments and you are simply awesome!!!

Good to know the flip problem is gone.

Is that possible to study the case further? Please help modify the data on top of it and add range limits, make or modify any constant based on the data to correct component position and send it back to me.

I will talk with the Math guy who major working on the solver and see if there is something we can improve for sure.

By the way, please try Drive the constrain instead of drag, as far as I know, drag may lead the value beyond limit boundaries and the result is not that obvious.

Please let me know if you have any more findings.

Thank you so much!

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 15:01:18 GMT

@Xun.Zhang

I have spend several hundreds hour on this assembly.

Most of the efforts are already documented in this thread Would you like to use flexible assemblies?

Now I posted this again to see if anyone can make it really work not getting into discussions and advices "how should you do it."

Please go through thread I give above. There are data sets and videos.

Cris.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 15:03:01 GMT

@Xun.Zhang wrote:
... as far as I know, drag may lead the value beyond limit boundaries and the result is not that obvious.
Please let me know if you have any more findings.
...

Drag would not lead to solution outside limits if props are properly limited.

Cris.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Curtis_W — Fri, 03 Aug 2018 15:43:17 GMT

Drag would not lead to solution outside limits if props are properly limited.

Hi @Cris-Ideas,

I don't have the time to go through the whole assembly, but I had a quick look, and one of the things that stood out to me was the use of sketches and work points for use in the constraints. I have not found that method to be a reliable way to work, and so I wonder if another approach would help.

Here's one example of an alternative approach to the "props" that came to mind for me, but I'm sure there are others. I'm not suggesting that this is the way you need to do it, but I would suggest thinking about some other approach to see if getting away from the use of workpoints and sketches helps.

As for dragging, keep in mind that you can often defeat the solver by dragging out side of the limits before your computer's processor has a chance to catch up and do the calculations... so dragging a complex mechanism can be unreliable sometimes.

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 17:06:18 GMT

Hi @Curtis_W

Thank you.

This particular prop is done because someone we have been testing if using ranges or flexible components is making trouble. Back than I have tried every possible approach for constraining and using this props. From few ways of using flexible components, through few different ways of constraining everything on the top level.

I understand that dragging can be dangerous. But if you drag carefully it should not be a problem.

Cris.

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

johnsonshiue — Fri, 03 Aug 2018 17:50:57 GMT

Hi Cris,

This is a case you and I took a look a while back. I think the key issue here is the concept of symmetry in the actuators. The both ends of the actuators have to move inward or outward in the same amount. Although there is degree of freedom, you cannot use one constraint to drive it. It is like you have multiple drivers in the system fighting each other. I personally think this is a limitation in the solver. I am not saying it is ideal. Nor do I think it should lock up like this. But, I don't see a solution to the problem at the moment.

Many thanks!

Re: Flat assembly destroyed, constrains flipped - FIX IT challenge

Cris-Ideas — Fri, 03 Aug 2018 17:55:45 GMT

@johnsonshiue

But I am not looking for the solution.

I posted this as a challenge. Look in the first post.

Lately there was very hot discussion how assemblies should be constrained, so I thought this is a perfect example for anyone willing to prove his theories.

Cris.