Constant Radius Curves. A Mainstay in Good Design

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Here’s an interesting question sent in this morning by a student:

Hi Graham,
I have started on the mesh and immediately have a question, kind of a fundamental one. On the Audi design the bumper has positional breaks as it transitions up and down.

Knowing this, does the curve I just drew still want to exhibit this kind of acceleration towards the ends (like on a hood) or not?

(Pictured below)

[G

(pictured above)

This is better for the bumper, I think.

Regards,
K]

Answer:

Hi K,

The first crv. you showed has acceleration at the top and bottom, but a lot of crvs. on a model are simpy Railway crvs. and originate from the Clay Modeller using a plastic crv. template to drag a curved. sec. along say the bumper. Similarly the windscreen is usually formed by dragging 2 or 3 different crvd. alloy splines accross the clay slab and then sometimes, the edges of the windscreen or roof would be accelerated by dragging railway crvs. with a tighter rad.

Summary:

Beauty is often best created with the use of geometry. The Designer knows this and will only fiddle with pure geom. in certain areas of the ext. So Yes! the second crv. which is a constant Railway Curve is what you should stick to, but remember in complex areas, this rule may go out the window. Generally this surface would be a simple constant rad, but if the highlights are not what the designer requires he/she may well want the edges accelerated.

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2 Responses to Constant Radius Curves. A Mainstay in Good Design

  1. Juan Maronese says:

    Hi Graham and Kevin,
    Its nice to see this tutorials, I just want to share an opinion if you guys don´t mind. Its true what Graham says about the railway curve, and it is going to work fine for that bumper for the first millings. But for an advanced step of the project it is better to give character to every curve/surface. Trying to take out the static feeling given by the constant curves. Dynamism is generated by the curve’s tension, and that tension is not present in constant curves. We can generalize and say that the only railway curve (radius between 3500 and 7000 approx.) we are probably going to maintain is on the roof surface between -375 Y and 375Y and then it accelerates before arriving to the pillars. In the other surfaces you will have what in Italian is called “invito”, that is a sort of acceleration or invitation to a radius or to another surface. Most of the times giving the G3 sort of curvature control. Last tip: constant, static, parallel, equidistant proportions, hanging feeling, are things you will like to avoid in Audi. keywords: sportiness, dynamic, progressive, tense, acceleration and quality. Hope its useful! Congratulations for the tutorial. Best

    Thanks to Juan Maronese for this very knowledgeable input. As a former clay modeller, I can add another layer of clarification, but saying that on early clay models a railway curve is dragged across the clay to form a static crv, but , yes! as Juan says, this would need to be made more complex, in order to add tension, as the model develops

    Regrads

    g

  2. Melville says:

    The model can be made more and more complex” That where Bezier and Nurbs converge”
    Imagine hanging a peice cloth between two constant railway curves you get a almost constant section loft
    In NURBS and polygon Modeling this is called Local control and Local refinement
    In real life it can be imagined by hanging a cloth between two railway curves and adding stents in midways
    so the cloth being “naturally continous” adjusts becoming primary secondary and tertiary surfaces under gravity
    Thus for bumpers we get five surfaces and max to max seven
    This Cloth behavior is carried forward to sheetmetal and we get our form tools and production highlights

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