DOFs Analysis Problems / BUGS - What is a DOF in invnetor?

[Cris-Ideas]

Hi,

I decided to split this thread from this one:

Constrain solving - as complicated as that

as this DOFs issue started to be to big to be still part of the original thread.

So fundamental question is

"What exactly are DOFs for Inventor?"

And before you start your post trying to explain to me that DOF is by definition Degree Of Freedom so ability of a component to move, please go through this thread at least from post #61, as it is not that easy as it would seem.

I encourage you to go through whole thread as there are very interesting examples of constrain solving issues and bugs that you may also be experiencing, as every Inventor user uses constrains and assemblies.

I anxiously await answer from solver team on What exactly DOF is for Inventor.

If you have examples or findings of yours in this matter please add comments.

Cris.

other interesting threads on constrain solving and flexibility:

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

Constrain solving - as complicated as that

flexible nightmare

Would you like to use flexible assemblies?

My youtube

[stephenrottloff7259]

Chris, Your tone casts a negative shadow on this USER FORUM.  Autodesk is not bound to answer your pointed software architecture questions.  Your main avenue of support should be your local reseller.  If they can't answer your type of questions, then posting them to a user forum makes little sense.  If your tone was different, many people would be happy to lend a hand.  Your are being your own worst enemy if you truly need assistance.  If your objective is to try and cast Autodesk in a negative light, try you might,  it will never change most people's opinion.  I could have spent 5 minutes trying to help you with an Inventor problem, but I figured those 5 minutes were better spent this way.

I hope you reflect on this and stop fighting yourself.  I will not respond to your posts anymore.

Thank you,

Stephen R.

[Cris-Ideas]

Hi Stephen,

Thank you for comment.

I am trying as hard as I can not to use "negative tone" as you described it. However because of lack of answers, from reseller (that is also not able to get them from Autodesk and advices me to write on the forum) or customer support it is very hard.

I document all cases in the way so they are clear and easy to follow. This costs me much time and I put a lot of effort to supply valuable data that can be base for illustrating the problem.

Numerous bugs have been documented and logged by Autodesk from my posts.

But in the same time I feel I am not even a step closer to answers to fundamental questions there need to be answered. I am also no a step closer to finding a stable reliable way of getting proper correct results from assemblies. 

Thread about Flexibility is over two years now and still answers and suggestions that are being given are not consistent and do not explain why thins work in the way they do.

Basically all what I am interested is to get answers, but this is not happening. There are many posts but hardly any answers.

So yes I may sound a little negative and frustrated.

In any case I try to stay on the subject and stick to technical aspects.

Cris.

[Cris-Ideas]

So with help of Customer Support I have found this:

"degrees of freedom

The variables by which an object can move. In assemblies, a body floating free in space with no constraints to another grounded body can be moved along three axes of translation and around three axes of rotation. Such a body is said to have six degrees of freedom. Constraints remove degrees of freedom by restricting the ways sketch geometry can change or a free-floating body can move.

"

This quote is from glossary of inventor help. link

This would confirm that DOFs should follow common understanding of this element of component positioning.

Therefore all differences of results of DOFs analysis from this definition are bugs, as design intent of the inventor development is as quoted above.

Assuming as above there are numerous problems related with this piece of software.

1) It is most probable that inventor uses results of DOFs analysis to "know" how each part can move. In such case it is no possible to avoid situation when components are placed against their constrains as DOFs analysis is failing to produce correct results in many cases.

2) Results of DOFs analysis presented to the user are not according to what they should be expected to be according to understanding of above given quote.

Cris.

[Cris-Ideas]

This video clearly shows that results of DOFs analysis in assembly do not follow definition of DOFs given in inventor help.

In this case part (cylinder) has indicated 0 DOFs when it obviously can move. Also depending on what is the constrain set that is active this part can have indicated 1 or 2 DOFs practically identical situation when only difference is it can translate along Y or Z of local coordinate system.

should you be interested in data set: https://autode.sk/2Lpgi10

So what is obvious from this simple video is:

1) DOFs analysis is not following definition of DOF given in inventor documentation

2) DOFs analysis gives different results in practically identical geometrical relationships between parts, thus it is not stable

3) various sets of constrains that define practically identical geometrical relationships are recognised differently and result in different results of DOFs analysis.

Cris. 

[Cris-Ideas]

Hi,

You may have already saw this video but I place it again as it shoes not only nonsense in DOFs analysis results it self, but it does also show how DOFs of various components constrained together are indicated as independent or "moving with".

In this case although components are clearly constrained so one moves totally with the other one they both have DOFs indicated separately (so  as we would expect) while in previous video they had DOFs not indicated clearly because "this component moves with the other one".

So clearly there is no clear human readable logic in how inventor deals with DOFs. Or et least there is no one who could explain this in general.

data set for download: https://autode.sk/2OeWe79

Cris.