&%%##^* Splines!!!

Discussion in 'Hangar Flying' started by Aerowerx, Jul 31, 2019.

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  1. Jul 31, 2019 #1

    Aerowerx

    Aerowerx

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    I hate hard splines in CAD!!

    I have been trying to learn devFus. But it uses hard splines. That means the line has to pass directly through the control points.

    When I put the control points where I want them, the formers look like they were designed in a pretzel factory! I'm sure the Skunk Works didn't have this problem with the SR-71.

    Why can't someone create a CAD program with a "French Curve" feature? Where the desired curve goes through the average of the control points, matching at the first and last points.
     
  2. Jul 31, 2019 #2

    Deuelly

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    Alibre and many others do this. I don't know what price range your looking at though.

    Brandon
     
  3. Aug 1, 2019 #3

    pwood66889

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    There are many types of splines in CAD. There may also be the "French Curve" in yours by a different name. RTFM... :)

    Percy
     
  4. Aug 1, 2019 #4

    Aerowerx

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    The programs devFus and devWing are specifically written for designing RC model aircraft. They cost IIRC about $70 Euro (each) for the non-CAM versions. The wing design wizard seems to work pretty well, though.

    Every time I have tried a CAD program I give up in frustration. I can make a pencil do what i want, but not those electrons!
     
  5. Aug 1, 2019 #5

    Aerowerx

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    Take a look at devFus and devWing. Their wizards are somewhat limited, but there may be a "manual" mode. I will have to look. I've only been playing with it for about a week now.
     
  6. Aug 1, 2019 #6

    Hot Wings

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    My old 2D program displayed splines just fine in it's native format. When I converted them to *.DXF they displayed like a bunch of facets. The *.DXF files did cut perfect CNC parts.

    My Solidworks will also at times display rather raged splines - but it is a result of a display setting, that I could change, to make things faster.
     
  7. Aug 1, 2019 #7

    pwood66889

    pwood66889

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    "I've only been playing with it for about a week now."
    I finished my wife's AutoCAD course and found it a lot to learn. Roger the pencil!
     
  8. Aug 1, 2019 #8

    Aerowerx

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    The problem is, I think, that is is a lot easier to program a "stiff" mathematical spline that is forced to go through the control points. Doing some kind of averaging curve fit is a lot harder. In other words, the programmers get lazy and take the easy way out.

    Let me think. I think it would be some kind of least squares curve fit, which takes a form of average of the control points and fits a curve with the least amount of error. No wild excursions like with a stiff spline.

    (Or have I swapped the definitions of "stiff" and "soft" here?)
     
  9. Aug 1, 2019 #9

    FritzW

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    Don't judge real CAD software by DevFus. ;) Fully (and easily) controlled splines have been around since the bronze age.
     
  10. Aug 1, 2019 #10

    Aerowerx

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    Yes, Fritz, but splines didn't become a real pain in the, uh, tail wheel, until the silicon age!
     
  11. Aug 1, 2019 #11

    FritzW

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    In "real" CAD splines are simple and easy but very powerful. I think the issue is DevFus, it looks like some pretty primitive stuff.
     
  12. Aug 1, 2019 #12

    Hephaestus

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    EAA offers ya a copy of solid works

    There's a free startup/hobbiest version of fusion360 available.

    Both do curves very nicely ;)
     
  13. Aug 1, 2019 #13

    wsimpso1

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    I do not know this software, but I have a couple ideas.

    If you know how many points for the spline, can you draw a random spline using that many points, then put coordinates on the points after? Perhaps you can skip coordinates when you set points and the spline, then add coordinates later. Perhaps you change the type of spline, many programs have more than one type of spline.

    Good luck

    Billski
     
  14. Aug 1, 2019 #14

    ScaleBirdsScott

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    I will concur on the idea that some freeware, or cheapware, type software may not have a lot of features like fancy splines, but anything that's been used in professional space for general CAD has had tons and tons and literal tons of spline options since essentially the beginning. If I'm not mistaken that was the entire impetus of developing CAD; to let designers and machines do fancy curves faster, and with more consistency over time, than laying it out the old ways. Thus CAD was born, to allow a machine to store all those points and poop out complex geometry on cue.

    The fact that more recent niche specialty programs approach their toolsets from an entirely different perspective is where you end up with programs that don't have the depth of options to do it right.
     
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  15. Aug 1, 2019 #15

    mcrae0104

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    AutoCAD does splines nicely, both "stiff" and "average" as you describe. I am using them to loft my fuselage.

    I haven't played with Dassault's free version of AutoCAD, called DraftSight, in a while, but I bet it does it too. You know, if you're into stone tablets and such like I am.
     
  16. Aug 1, 2019 #16

    Foundationer

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    Draftsight is quite limited re. Splines from what I've seen but getting a decent result is not too difficult and the program overall is really good IMO. AutoCAD knocks it into a cocked hat though and you can get it for free by clicking the 'i'm a student' button (and who here isn't a student really?).
     
  17. Aug 1, 2019 #17

    bmcj

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    I did a Google search for &%%##^* splines. I found lots of search results for splines, but nothing for the &%%##^* type of spline.
     
  18. Aug 1, 2019 #18

    FritzW

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    &%%##^* splines are proprietary and used only with devFus.
     
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  19. Aug 2, 2019 #19

    Aerowerx

    Aerowerx

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    No they are not proprietary. I have encountered them elsewhere. Like the fuselage design part of XFLR5.

    The problem is that you make a small change in a control point and the curve makes some wild excursions, sometimes even curling back on itself forming a loop. Kinda hard to build a fuselage like that!
     

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