How to constrain a line so that it is normal to a conical curve

[Anonymous]

I am working on a mini toy crossbow when I encounter this issue. I tried different ways to constrain a line so that it is normal (perpendicular to the tangent line) to the parabola and/or it's offset curve such as creating a tangent line on both curves, set a coincident to both ends of the line and setting the length to the offset distance and directly using perpendicular constrain, but all of them returns with an error.

I also need  to set a distance between the line and the center of the circle.

The line in question is the unconstrained one

Since I taught myself how to do everything from CAD to production I think I must have erred in some way. Yet I am running out of time in this summer vacation so I put this in design section instead of the report bugs one so I can find ways to do it instead of pointlessly arguing about the problem.

[chrisplyler]

Like either one of these? I didn't know whether you want it perpendicular to the regular line, or perpendicular to the dashed construction line, so I made both.

You are confusing me, by the way. None of those curves is a parabola. They are all constant radius, and a curve of constant radius is called an arc. Also, any line that is normal (perpendicular to a tangent line) to an arc must pass through the center point of that arc, having zero distance between itself and that center point.

[Anonymous]

Sorry I didn't make it specific but the two "lines" on the side are not straight lines but a part of a parabola, I want to make it a normal line so that I don't need to change the angle of that line (which is for making a hole for the bowline) if I want to change the bow shape again.

[chrisplyler]

OH!

Good luck with that. F360 lacks the ability to constrain things tangent to any irregular curves. Don't get me started. And if you can't constrain anything tangent to it, then you can't constrain anything else perpendicular to the thing which isn't tangent and expect it to be normal to the curve.

Send your complaints to Chad.

[Anonymous]

Is there any work around that I can use. And how did that offset constrain arrow manage to stay normal to it?

[wmhazzard]

Place a point in the center of your line, then draw a line from the line center to the circle center. Then you can make your line perpendicular to the center line. 

[MichaelT_123 · Accepted solution]

Hi Mr Dictsui2003,

As pointed by Mr Chrisplyler dealing with exotic? curves can bring some challenges  from time to time.

On this occasion and the case you shortly described they were smooth and obedient. 

Please have look at the files attached. They (I hope) are self explanatory and you will be able to adopt the methodology to your design.

Addendums:

MP4 video_mono:

https://a360.co/2yUxLdQ

MP4 video_stereo:

https://a360.co/2YEL5Cu              (viewing requires red/cyan anaglyph glasses)

Regards

MichaelT

[Anonymous]

Did you mean that if I need to create tangent lines to those curves I must create an end point for it? It will be quite bothersome if I need a lot of them.

[chrisplyler]

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@wmhazzard wrote:

Place a point in the center of your line, then draw a line from the line center to the circle center. Then you can make your line perpendicular to the center line. 

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That looks close, but it won't actually make the line normal to the parabola. Go ahead and drag the line down towards the bottom of the parabola. You'll see.

[MichaelT_123 · Accepted solution]

Yes and No Mr Dictsui2003,

As with any software, it is essential to not only have the first glance of it but also explore hidden crevices of its nature. Programs are written by humans who by their profound fallibility have a negative impact on the final product. This must be taken into account,… no human is perfect |😊.

Conic curve software implementation is the perfect example of it ( but,… no example is perfect |😊 ) :

• The foundation of the sketch/model is based on points
• Curves are their overlays, and they are constrained by points
• In terms, curves have their internal coordinates called evaluator’s parameters
• While these concepts are digested ( with the help of references)
• Move to conic curve
• A conic curve can be circle, ellipse, parabola or hyperbola dependent upon rho value, not necessary parabole Mr Chrisplyler,.. but no CADman is perfect |😊
• Its 2D equation (without a position in coordinate space) is based on 6 scalar parameters
• In F360 engine, it is coded/represented (with its place, as I understand) by three points and likely a scalar(s) not visible to the public in the post-creation stage and certainly not to be set up as userParam (the predicament, which makes life more exciting but,… no software is perfect |😊
• So if you ‘need a lot of them’, the F360 engine will willingly process these limited number of points and a scalar(s).
• The curve you see on a screen does not exist! But… no screen is perfect |😊
• As conic curves (like parabole, hyperbole) are quite exotic, think about a circle.
• Would you object having them as many as necessary?
• ‘if I need to create tangent lines to those curves I must create an end point for it?’
• Yes, tangent/normal line must have the anchor point on a curve.
• However, there are only two points on it,
• but… no curve is perfect |😊
• Much more, if you will force a sideline segment to be tangent to a conic curve via F360 UI you will discover that the line will become the tangent at endpoint only, but…no UI is perfect |😊
• One can create tangent/normal in F360 system by other ways at a selected point on the curve. It depends upon the answer to the question:
• But... Is my geometry skill perfect? |😊
• If yes,… so what are you doing here?
• If not,… ‘be quite bothersome’. It does not mean ‘lazy’, does it?
• Yes, I am a geometry wizard. Where can I get the equation of the curve so I can start numbers-crunching?
• Well, nowhere. The subject is not documented!
• But,… no reference is perfect |😊
• So even if you perfectly slalom through these imperfections, mind you that
• the ‘conical curve’ machinery does not mesh well with the rest of pieces of F360 engine
• because,… no CAD engine is perfect |😊
• So substantial these imperfections are that they equate to failure. It is perhaps not only my opinion but also has been collaborated by many posts on this forum over the years.
• But,… no opinion is perfect |😊
• My final advice is: unless there is extremally specific reason to avoid conic curves. Use splines instead.
• They are less imperfect |😊

Addendums:

MP4 video_mono:

https://a360.co/308zus3

MP4 video_stereo:

https://a360.co/2N8O5QQ              (viewing requires red/cyan anaglyph glasses)

Regards

MichaelT

[Anonymous]

Thanks for replying to my question, in which you gave me some information for me to find a "close enough" solution myself. But would you kindly post the f3d for that file, I only keep it unsolved because I think someone will find it useful later on and I have already used the circle method to finish my job.

My Solution:

I made a construction line on any 2 points on the curve, then I set a very short length for the line. The line should be quasi-tangential so the line perpendicular to it at the midpoint should be quasi-normal as well