Freecad says "Fully constrained sketch", but it's not

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Tomas
Posts: 86
Joined: Tue Feb 09, 2016 4:40 pm

Freecad says "Fully constrained sketch", but it's not

Post by Tomas »

Hi all,

I am having some trouble but probably you will immediately see what I am doing wrong here.
Freecad says that the sketch is fully constrained but when I look on it I can tell that is it not.
The issue is then that sometimes when I open the file, the sketch is changed to the other solution.

Please see the attached file.

Description:
The small circle is located on the line of the larger circle in the first quadrant.
But the constraints applied are also fulfilled when the smaller circle is in the fourth quadrant.

Any ideas?

Have a nice day,
BR
Tomas

I am using:
OS: Windows 7
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.6706 (Git)
Build type: Release
Branch: releases/FreeCAD-0-16
Hash: f86a4e411ff7848dea98d7242f43b7774bee8fa0
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17
fullyConstrainedSketch.jpg
fullyConstrainedSketch.jpg (465.06 KiB) Viewed 2019 times
Attachments
fullyContrainedSketch.FCStd
(2.99 KiB) Downloaded 51 times
Last edited by Tomas on Fri Apr 28, 2017 6:07 am, edited 1 time in total.
chrisb
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Re: Freecad says "Fully constrained sketch", but it's notH

Post by chrisb »

Fully constraint doesn't mean that the solution is unique. It means there is no more an infinite number of degrees of freedom solutions.

Edit: Thanks DeepSOIC, it should be solutions not DOF.
Last edited by chrisb on Fri Apr 28, 2017 7:52 pm, edited 1 time in total.
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Tomas
Posts: 86
Joined: Tue Feb 09, 2016 4:40 pm

Re: Freecad says "Fully constrained sketch", but it's notH

Post by Tomas »

chrisb wrote:Fully constraint doesn't mean that the solution is unique. It means there is no more an infinite number of degrees of freedom.
Ok, that's a pity. I knew it was something I misunderstood :D
Thanks,
BR
/Tomas
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microelly2
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Re: Freecad says "Fully constrained sketch", but it's not

Post by microelly2 »

Tomas wrote: The issue is then that sometimes when I open the file, the sketch is changed to the other solution.

Any ideas?
If you have at least one distance constraint then there is a quadradic equation in the system with 2 solutions,
to avoid this you can replace some constraints
(example use an angle and deactivatet the distance (blue), then invert the angle and roll the constrains back angle blue and distance red )

I had the same problems some day ago and I will upload the example when I'm home again.
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DeepSOIC
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Re: Freecad says "Fully constrained sketch", but it's notH

Post by DeepSOIC »

chrisb wrote:Fully constraint doesn't mean that the solution is unique. It means there is no more an infinite number of degrees of freedom.
Correction. 1 degree of freedom means the solution space is 1-dimensional. "Space" implies an infinite number of solutions. Finite number of solution isn't a degree of freedom. And sketcher will tell you the sketch is fully constrained if there are no degrees of freedom, and it can't detect there are extra discrete solutions.
Tomas
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Joined: Tue Feb 09, 2016 4:40 pm

Re: Freecad says "Fully constrained sketch", but it's not

Post by Tomas »

microelly2 wrote:
Tomas wrote: The issue is then that sometimes when I open the file, the sketch is changed to the other solution.

Any ideas?
If you have at least one distance constraint then there is a quadradic equation in the system with 2 solutions,
to avoid this you can replace some constraints
(example use an angle and deactivatet the distance (blue), then invert the angle and roll the constrains back angle blue and distance red )

I had the same problems some day ago and I will upload the example when I'm home again.
Ah, yes ofcourse that is how to do it!
But if for instance the value comes from a spreadsheet I will need to do the math myself, but I can, so that is no issue.
Great!
Thanks and have a nice weekend!
BR
Tomas
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microelly2
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Re: Freecad says "Fully constrained sketch", but it's not

Post by microelly2 »

here my example file and the demo script

open the sketch
the copy and paste the srcipt to the python console
it demonstrates how to flip between the two solution s
viereck_unbestimmt.fcstd
(3.85 KiB) Downloaded 51 times
viereck_unbestimmt.py
(1.08 KiB) Downloaded 76 times
Tomas
Posts: 86
Joined: Tue Feb 09, 2016 4:40 pm

Re: Freecad says "Fully constrained sketch", but it's not

Post by Tomas »

microelly2 wrote:here my example file and the demo script

open the sketch
the copy and paste the srcipt to the python console
it demonstrates how to flip between the two solution s

viereck_unbestimmt.fcstd
viereck_unbestimmt.py
Thank you very much for your effort!
Maybe one should learn writing pythonscripts!
I wish you a great day,
BR
Tomas
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microelly2
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Re: Freecad says "Fully constrained sketch", but it's not

Post by microelly2 »

Tomas wrote: Maybe one should learn writing pythonscripts!
There are often situation where the gui does not support special actions but FreeCAD has a large programming api.
writing scripts allows you to automate common tasks.
And python is a very fast way to write scripts.
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