One single constraint and I can't rotate my part - why?

[tabrakecc]

Howdy.  Inventor 2014, but I had the same problem when I used 2011.  It happens all the time!  Compenents freeze up when there are still DOF available.  Usually happens in larger assemblies, but I have 16 GB of RAM and only using 28% of it.

I have a simple mate that I'm trying to do to a subassembly.  Right now, I selected two cylindrical features thru the constraint dialog, and mated them.  I haven't even added a mate yet to constrain it in any other way, and it won't budge.

Sure, I can create mates, then it will move, but I want to grab the dang thing and swing it from one end of travel to the other and look at clearances!!!

What am I doing wrong?  OR are they just always this flaky?

thanks

[tabrakecc]

While I'm waiting, I continue to use workarounds like I always do.

I apply an angle constraint, to force the rotation of the component where I want it.  I want to start at 0 degrees, but Inventor things that parallel is negative 180 degrees.....  Ok, then, have it your way.  I change it to -165 degrees, which is the area where I need to check clearance.

So then, I supress the cylindrical mate, and add a "ball socket" joint instead, which is really what this is.  I want to add some "up angle" to the ball joint.

So I start with a frame member in the same plane as my component, and since it would not predict the angle for me, I accept 0 degrees, thinking I'll tweak it in just a second.

When the mates solve, now, the -165, has put the component on the OTHER side of the reference surface.  It still says -165, but it's 15 degrees on the other side of the reference, and 30 degrees from where -165 was a second ago.

What is wrong here?  This happens to me all the time, this dang thing doesn't have parallel or perpendicular mates, and the angle mates seem impossible to predict, and when you finally have it figured out, the stupid thing reverses itself!!!!!!!!!!!!!!!!!

I am beyond frustrated, can somebody explain to me what the heck is going on here?

[JDMather]

Attach assembly here.

Note that there are several types of Angle constraints.

Which one are you using?

[blair]

When ever I have a part that "locks" with only a single constraint, I look for a bad constraint somewhere in my IAM. If the icon is not grey'd out you have a bad constraint. This tool will then highlight all the bad constraints

[tabrakecc]

Blair:

Well, you got me there. There are in fact, numerous mate issues. This is a top level assy that I'm repurposing for a redesign.

There are hundreds of mates, of course, so it's not a perfect scenario.

I'm capable of fixing mates, though I have to say that I find in many cases, Inventor is not as capable as other systems at allowing you to redefine mate references. It seems to let you pick a new one if it's disappeared, but it doesn't let you "deselect" as far as I can tell.

I didn't want to delete all of these as I wasn't sure if they were part of the hundreds of hardware pieces I have currently suppressed.

How do the mates of suppressed components display? If the troubled mates are from these suppressed components, can I just suppress the mates so I can continue to work and sort them out later?

Thanks

[swalton]

To change the references of a constraint (IV 2014):

1. RMB on the constraint, select edit.

2. Click on the selection button in the upper right hand corner to clear the existing reference and then select a new one in the model.

3. Click "Ok" to accept your changes

I don't think there are any changes in IV 2015.

Edited to add:

I would not expect any assembly with broken constraints to solve reliably, even if those constraints are to suppressed components.  I believe IV tries to solve constraints to suppressed components.

I would supress the broken mates and ground the respective components while you fix the assemblies.  If you must rush a design out, you can keep the constraints suppressed, but how do you know that the components with the broken constraints are in the correct location?  Will that matter for your new design?

[tabrakecc]

I'm aware of all that, except the selection part.... I'm used to seeing the selections graphically, and being able to click them again to deselect, or pick the selection from the dialog box, verify it's the one you want to delete, then use the delete key.

I'll have to experiment with this to see how it works. Just seems you'd want to be able to verify which reference you're deleting before you delete it.

[swalton]

I almost always use the same selection order when I place constraints.  The 1st selection is the component I want to move and the 2nd is the stationary reference.  That way I have a habit that helps me remember what goes to what.  Your color scheme should have one color for the 1st selection and another for the 2nd.  Those colors should match between the geometry selection and the arrow underline in the constraint window.  Use those for feedback too. 

Finally, try checking the "Display component names after relationship names" box in the Assembly tab of the Application Options.  That will show the names of the two components used in a constraint in the model browser.  The first name is the first selection, the second name is the second selection.

[kmeldfreyssinet]

Hi,

I am also having some issues with constrains when editing old assemblies for new projects.

I noticed (what is quite obvious) that if you have any constrain corrupted (Inventor gives you warning of bad or inconsistent constrain) then in such case nothing will work until you fix it, or disable. So in such case I either suppress all bad constrains, create new one and than fix them one by one to fit my new scenario or delete all bad and create new once to reduce unwanted DOF.

In fact in some build in colour schemes both members selected in for a given constraint have same colour. (winter night). This is strange but obviously Autodesk had some idea for it.

Angle constrains are also a trable for reasons mentioned above. I personally try to use "explicit reference vector" as often as possible. However strange thing is that I am not allowed to select origin axis of assembly for reference vector even when I select one of origin planes for one of constrained members.

Cris.

[blair]

I find that suppressing a Contraint works as it's no longer in conflict. As I posted as soon as I see my part locking after only 1 constraint I know I have a bad/sick constraint to fix.

[tabrakecc]

Thanks guys. Some CADs will deal with a few broken mates, some don't. Could be that I suppressed the parts and moved stuff around, assuming that the mates were also suppressed. Maybe that's when this started. I've been working around it, but in this case, I cannot do the work in a smaller assembly, it's got to be done here at the top.

Cris, I'm going to try using the "ref vector" angle mates. The other ones seem wholly ineffective because they seem free to change their reference. THIS is a bug! I'd say "why bother having any other angle mates" but of course, when you just need a simple mate and there's already a pivoting constraint it seems should be unnecessary to specify ref vector.

I've wasted a lot of time trying to figure it out, only to figure out it's the broke constraints that are probably stopping me. I will fix them and report back.

thx

[JDMather]

If you are not using logical sub-assemblies - you probably should be.

Makes constraining, and perhaps more importantly, diagnosis of "sick" constraints far easier.

And the real world is generally built from sub-assemblies.

[kmeldfreyssinet]

Hi,

What I noticed using "explicit reference vector" angle constraint is that the vector has direction and in consequence angle direction is also specified so negative is negative and positive is positive.

Cris.

[johnsonshiue]

Hi! Inventor is capable of solving assembly constraints when some constraints are sick. It depends on the type of failures and how the assembly is contrained. The result can be unpredictable sometimes. Locking behavior usually means the component you are trying to constrain has limited degree of freedom due to other constraints or failures. It is very hard to tell where the problem is without seeing the model. I suspect there might be tangent constraints, which can lock DOF of certain components in the loop to avoid too much freedom. If possible, please attach it here or send it to me directly (johnson.shiue@autodesk.com).

As other members suggested, you can suppress (or fix) the sick constraints and it should help free up the component. Suppressing components does not help since LOD Suppress is a memory management tool which does not interfere any design change (geometry, position, and others).

Many thanks!

[Anonymous]

IT IS NOT SOLIDWORKS, THAT'S FOR SURE