Issue - Pad error (Bug?)

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Shalmeneser
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Re: Issue - Pad error (Bug?)

Post by Shalmeneser »

Can you explain the blue line/path between the wall ? Do you need parabola ?
And the blue diagram at the bottom ?
drmacro
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Re: Issue - Pad error (Bug?)

Post by drmacro »

As for your sketch.

With nearly 1000 constraints it does go against all recommendations of "the simpler the sketch the better".

Each constraint in a sketch adds to the solver matrix. So, the solver has to solve each and every constraint every time the model recomputes (read: with every change you make).

It is interesting how you've used construction geometry.
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lordsansui
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Re: Issue - Pad error (Bug?)

Post by lordsansui »

Shalmeneser wrote: Sat Oct 01, 2022 7:21 pm Can you explain the blue line/path between the wall ? Do you need parabola ?
The blue lines are related to two things:

What they called advanced centerline witch is a method to improve accuracy between the software that calculate loundspeaker response vs the 3D model and it's because you need to fold the horn.

The second reason, is because the horn has an expansion, so each increment of length will increment the area (parabolic expansion), so you need a lot of constrains and auxiliary geometries to keep the correct expansion while folding.
Shalmeneser wrote: Sat Oct 01, 2022 7:21 pm And the blue diagram at the bottom ?
The blue diagram at the bottom is just an unfolded version of the loundspeaker, it help to check error due to the amount of involved contains, but it uses simple ones.

The folding parts are the ones the consumes a lot of constrains. See the attached schema, during the fold, the start and the end have different sizes. You can try to solve it with less constrains, simulate with the parameter you found, build a loundspeakers, measure it and check the accuracy. This method was not developed by me and it was already proved to be good, I just replicate it.
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lordsansui
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Re: Issue - Pad error (Bug?)

Post by lordsansui »

check also this attached image to see some influence in the length
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chrisb
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Re: Issue - Pad error (Bug?)

Post by chrisb »

lordsansui wrote: Sat Oct 01, 2022 7:12 pm I'm not an audiophile, but I'm engineer, and there is reasons for things to exist and to be done in a specific way, you liking it or not, and criticizing my sketch not knowing in the first place the reasons behind it isn't wise from your side. The help request was related to PAD issue. Is't not a problem if you don't like my sketch, it's just that you can hold this option for yourself if it doesn't contribute to fix the issue.
You hopefully went back to Bance's first post and saw that he was the first to answer your post.

Concerning the comment on your sketching, I would say it is on the good side of the unsharp border between off topic and general recommendations on a model. To rephrase your own words: there is reasons to do sketches in a specific way. Usually newbies are rather thankful if they get hints on general defects in their models, but that's not all. Bance is a well known forum regular, his word has weight, as we say here. Other newbies may see this topic and at least they should know, that there are good reasons to sketch differently.
If such things slip through uncommented, it may seem to be ok, because it had been reviewed by someone who knows how to do it right.
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lordsansui
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Re: Issue - Pad error (Bug?)

Post by lordsansui »

Bance wrote: Sat Oct 01, 2022 3:09 pm Probably the worst sketches I've ever seen by the way.
@chrisb tell me what the above comment helped me or any other user?

I'm greatfull for all the help I received including his one, and I wrote that.

I will not take the bance's comment longer, I'm not a forum's manager, hi is adult and can reflect about.
lordsansui
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Re: Issue - Pad error (Bug?)

Post by lordsansui »

chrisb wrote: Sat Oct 01, 2022 10:02 pm If such things slip through uncommented, it may seem to be ok, because it had been reviewed by someone who knows how to do it right.
Shalmeneser make questions about the skecth and I post the answers.

If you just reproduce a specific loundspeaker layout, you can use just a few sketches or even not using any, like Google sketchup, it will be easy, but if you are designing a loundspeakers and need a paremetric 3D that will adjust everything for you regarding the dimensions you change. I think that this is the reason to use parametric sketches. In this sense, sometime things start to became complicate.
Batucada
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Re: Issue - Pad error (Bug?)

Post by Batucada »

Bance wrote: Sat Oct 01, 2022 6:21 pm Oh an audiophile..... don't forget to line the inside with fairy dust, and gold plate the connectors. :lol: :lol: :lol: :lol:
Hi,

I followed the thread at the weekend and was inclined to chime in, thanking @Bance for his humour. But then I refrained from doing so. However, the basic topic of this thread does not leave me alone, especially since I have taken the opportunity in the new project that is currently underway to make appropriate tests. Basically, I have internalised the rule in PartDesign to use only one pad per body. But sometimes my fingers tingle. I tried it and it worked. Later, with a completely different object, with which I wanted to represent an element of a roller chain, it also worked to add a second pad to represent a flap. So far so good. Overconfident, I wanted to add the third pad to represent the second flap on the opposite side. FreeCAD also let me do it and didn't grumble, but the result was scary.

There seem to be fuzzy rules for delineation in PartDesign. Sometimes the intention to create 2 solids in one pad is nipped in the bud. On the other hand, it may be possible to "glue" another pad to a construction within a body at a later stage. However, I will certainly stick to the rule of using only one pad per body, because trial and error is too costly for me. Finally, because of the message in FreeCAD, which is ambiguous, I am left with the question, will this "forbidden" way perhaps exist at some point, because perhaps a development is being pursued in this direction?
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onekk
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Re: Issue - Pad error (Bug?)

Post by onekk »

lordsansui wrote: Sat Oct 01, 2022 8:54 pm check also this attached image to see some influence in the length
Probably seen from a sound engineer the problem is sharp angles that cause reflections, and "counter pressure", in fact some "high end" speaker system don't use a "cube" as shape but a polygon with angled sides calculated to reduce reflections, but many years have passed since I've seen these "research", probably some advancement has been done, and other design could be found.

There are many design, if you have to make with "wood" you could model the angle "not 90 degree" and recalculate things, in the old days I have seen some Woofer "charged" using sound PVC pipes with 90 degree curves cut with some accurate lengths.

EDIT: But your final design shown has not 90 degree angles, so probably the example is not done for the image you have shown.

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Bance
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Re: Issue - Pad error (Bug?)

Post by Bance »

Batucada wrote: Wed Oct 05, 2022 8:26 amI have internalised the rule in PartDesign to use only one pad per body.
One may have as many Pads as the heart desires, there is no restriction as to this.

The is same is true for pockets, revolves or any of the other constructive geometry tools.

There is however the proviso that there may only be one continuous solid in the Body.

This means that additive geometries must be in contact, and subtractive geometries may not cut through, such that a separate solid is formed.

In terms of contact, there is a well known problem in OCCT that occurs in certain situations, we refer to this as the Co-planar issue.

This usually manifests itself where solids are tangentially connected, Overlap is the most secure way.
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