Control Point Spline

[Fully_Defined]

Here is a public link to the design: https://a360.co/2ZYXJex

I am having trouble with a control point spline only accepting useless values as inputs. In the case of the sketch in the link, the 25mm in X value defining the spline is the ONLY way I could fully define it. No combination of other dimensions - which are actually important, BTW - could be used as driving dimensions. The 22.394mm driven dimension is in fact the critical dimension, and I would like it to be 20mm.

My intention was to use the angle between the construction lines of the spline to control the curve, along with the height of the terminus.

How would you go about solving this?

I feel like this could be a glitch, but I'm willing to entertain that I just don't know what I'm doing wrong.

[Fully_Defined]

If I add more control points, I can control more things. I guess that makes sense.

[LeonardoBN]

Hi David.

I tried to constrain the sketch you shared (based on the 20 mm and angle). Screencast.

I achieved it using a different order of commands, which I wouldn't think at first. I suppose the main issue is the Coincident constraint between spline and 250mm-long line. Fusion doesn't allow us to change the height of the terminus after the Coincident (it's just a observation, not a rule I saw). I had to delete Coincident constraint and the line dimension, add the terminus length, and then add Coincident again.  🙄

[g-andresen]

Hi,

If the coordinates of the start and end points of a control point spline are defined, you have to decide whether you want to define the remaining control points (angles or lengths) or an additional line between start and end point. Both is not possible.

günther

[Fully_Defined]

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@g-andresen wrote:

Hi,

If the coordinates of the start and end points of a control point spline are defined, you have to decide whether you want to define the remaining control points (angles or lengths) or an additional line between start and end point. Both is not possible.

günther

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I see what you did in the third example, which is almost exactly what I wanted to accomplish, except 218.997 is clearly not a value you can change. I ran into the same problem where I could convert a dimension into a driving dimension, which converted the spline to fully constrained, but I could not edit the value.

To summarize:

Example 1: NOT ideal
Example 2: NOT ideal
Example 3: NOT ideal. Closer, but 300mm is unimportant and 218.997mm is not 219.000mm.

To clarify, my issue isn't the limitation on how many constraints are available - because I only need a few -  but the random nature of WHICH constraints I am allowed to use versus which I can't.

Here is a public link to the exact same design, but with a fit point spline and requiring too many constraints to fully define. A change in any one dimension would break the smooth curvature of the spline:

https://a360.co/3f3EiFI

Here is a public link to the original design with the inputs I WANT to use, minus the coincident constraint that I NEED:

https://a360.co/2BxIwYB

And of course the elephant in the room:

This sketch includes all of the geometry I would need to fully constrain this spline.

[TrippyLighting]

I've run into oddities with constraining and dimensioning control point splines a number of times and would believe this is a bug.

@ryan.bales can you help?

[MichaelT_123]

Hi Fellows,
Taking into account my sense of the sketch constrains algorithm, in general cases, it is permutation sensitive.
It means that the order in which constrains are applied matters.
One can imagine other ways to construct a sketch constraint’s graph, but the current method is relatively fast and straightforward.
There is also another, perhaps the most essential benefit... it outsources some tasks to human brains in effect increasing the species intelligence pool.

Without the proper intell-resources we will be overwhelmed by our enemy.. AI.

Regards
MichaelT
P.S.
I have posted while ago

thoughts about the subject while ago,... but can't find it -).

.

[Fully_Defined]

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@MichaelT_123 wrote:

Hi Fellows,
Taking into account my sense of the sketch constrains algorithm, in general cases, it is permutation sensitive.
It means that the order in which constrains are applied matters.
One can imagine other ways to construct a sketch constraint’s graph, but the current method is relatively fast and straightforward.
There is also another, perhaps the most essential benefit... it outsources some tasks to human brains in effect increasing the species intelligence pool.

Without the proper intell-resources we will be overwhelmed by our enemy.. AI.

Regards
MichaelT
P.S.
I have posted while ago

thoughts about the subject while ago,... but can't find it -).

.

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WTF???

[Fully_Defined]

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@TrippyLighting wrote:

I've run into oddities with constraining and dimensioning control point splines a number of times and would believe this is a bug.

@ryan.bales can you help?

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@TrippyLighting The elephant in the room:

Of course I can already do this in Solidworks, so I don't actually wonder if it's possible. Definitely a bug in Fusion.

How many boats were never made because of this problem? LOL

[g-andresen]

Hi,

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@Fully_Defined wrote:

I see what you did in the third example, which is almost exactly what I wanted to accomplish, except 218.997 is clearly not a value you can change. 

 check this out:

By the way, I agree with @MichaelT_123  that when dealing with splines, the feeling for form is in the foreground and dimensions fix the form afterwards but do not change it.

günther

[Fully_Defined]

By the way, I agree with @MichaelT_123  that when dealing with splines, the feeling for form is in the foreground and dimensions fix the form afterwards but do not change it.

günther

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@g-andresen That is not the answer I was looking for. Also... that's not how CAD works!

[TrippyLighting]

I might just be a dumb old elephant soon to be replaced by AI, bust based on some anecdotal evidence collected in some other CAD applications I believe there is either a bug here or some general behavior that needs fixing. Below are screenshots of three applications where this sketch can easily be created fully parametric and constrained.

SolidWorks Professional 2017: 

 

Autodesk Inventor Professional 2021:

ZW3D Professional 2020:

[JamieGilchrist · Accepted solution]

Hi @Fully_Defined 

there's a bug in our sketch solver logic for this case.   I'm sending this off to the development team to investigate.  In the meantime I've got a workaround for you (sort of).  Following the video, I can get to a fully constrained sketch in (what I think) is the dimensioning scheme you're after, however, there's a conflict between the 20 mm dimension (which now shows as a driving dimension, but is behaving like a driven dimension) and the Horizontal constraint at the bottom hull of the spline (you initially had a tangent constraint for this).  This is a clunky workaround, I agree.

For Autodesk reference, I've created this bug FUS-69725

[MichaelT_123]

Hi Mr. JemieGilchrist,

It looks like the constraints are the same, but the order in which they have been applied is different. Am I right?
First, all construction points of interest are put into place, and then a spline is assigned.
In other words, do assemble a jig and bend a sheet onto it... seems logical...
The initial approach was - bend a plate and force it into a position. Although it is theoretically possible, it requires more effort and strength. In other words, the solver must perform the calculation globally on the whole constraints set, not locally like with the first construction method.
As I posted in the previous note, it looks like the current constraints algorithm is a local one. It will work only to the first fail, and it won't attempt to find the global solution. AI is not built-in yet, so for good or bad, the outsourcing is required... from time to time :).

Regards 
MichaelT

[Fully_Defined]

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@MichaelT_123 wrote:

Hi Mr. JemieGilchrist,

It looks like the constraints are the same, but the order in which they have been applied is different. Am I right?
First, all construction points of interest are put into place, and then a spline is assigned.
In other words, do assemble a jig and bend a sheet onto it... seems logical...
The initial approach was - bend a plate and force it into a position. Although it is theoretically possible, it requires more effort and strength. In other words, the solver must perform the calculation globally on the whole constraints set, not locally like with the first construction method.
As I posted in the previous note, it looks like the current constraints algorithm is a local one. It will work only to the first fail, and it won't attempt to find the global solution. AI is not built-in yet, so for good or bad, the outsourcing is required... from time to time :).

Regards 
MichaelT

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@MichaelT_123

I recommend not changing fonts and colors in your responses. It's clear that English isn't your first language, and adding visual effects makes it even harder to understand your meaning, among other things. I still have no idea what you were trying to communicate.

But... from what I could decipher, you are absolutely on the wrong track. This conversation is about a single spline that cannot be produced using standard methods available to all applications. There is no legitimate reason why I would not want to produce this spline, or to do it in a different order.

Is that your argument? That I should not want to produce this spline?

[Fully_Defined]

@JamieGilchrist Thanks for the acknowledgment. Think of how many boat projects have ended in heartbreak instead of setting sail!

[JamieGilchrist]

boats?  I though you're building bikes?  😉  One other thing you can do to get you through is don't worry about fully constraining your spline, over build it and set a sketch point on the spline at your 20 mm dimension.  You've got your angle, the anchor point tangent at one end, the spline coincident to your construction line and a reference point at your desired 20 mm.

[Fully_Defined]

@JamieGilchrist Lately, starships. But this one's for the water.