Creating ergonomic/organic surfaces

Rob_Ku

Hi community,

With my current project, I have hit an obstacle. I'd like to better be able to create organically shaped surfaces with OnShape's surface tools. However, often it happens to me that I am just unable to arrive at the shape that I intend. Within the scope of this question, I'd like to examplify this with a seat that I am trying to re-model from a product that is already existing. I also hope to learn about how to use the surface tools better or smarter, so please feel free to elaborate in length if you like.

So let's get to it:

The seat that I am trying to model should look somewhat like this:

I have started modelling this seat by using splines and projected curves.

First a spline for the section view:

Plus an additional closed cuve (grey shaded enclosed area). If I use the "Projected Curve" tool, the result will be the orange curve, which I can then use the "Fill" tool on to create a surface.

This is point at which it becomes difficult - I'd like to add the support wings at the sides of the seat.

If you look back up at first 2 images (the ones of the already existing seat), you can see some wings at the sides of the seat that support the back from the sides, so that sliding off the seat is prevented (circled in red on the 2nd image). I have tried multiple approaches, but it is really hard to incorporate such shapes in the model.

I have tried adding more curves and the projected curve tool again, but unifying the resulting surfaces with the already existing curve of the seat is really difficult. For example, it seems to me it would be useful to be able to place verticies along a curve so that I can use the bridging curve tool better. However, there is no such function. Also, I cannot add verticies by making a plane that intersects with the orange seat curve and use the "intersect" or "use" tool. Apparently they don't work with curves/splines.

Another approach I tried was shaping the section view spline (image number 3 from the top) such that the wings are already included. Then I tried using the "guides" function to create the shape, but the results were less than satisfactory.

I'm taking into account that I am simply not yet well versed enough with the surface relevant tools. I have read up on how to use the tools in the help section, and I have watched the webinar about surface creation by Cody, but it seems this doesn't help me with my problem. If there are technicalities about the surfacing tools that I haven't figured out yet, please educate me a bit about the details or point me in the right direction. If it's not so much a question about the tools and functions, but rather about the approach, please let me know how you would recommed doing it.

Looking forward for your help, thanks in advance!

MBartlett21

Please see this discussion about surfaces and trimming/extending them
https://forum.onshape.com/discussion/comment/40624/#Comment_40624

Maybe ask @billy2 for help

billy2

Easy, firstly this is a surfacing problem, second identify your main patches, third figure out your transitions between patches.

Just throwing this out there.

1. you have a good definition on one of the surfaces.
2. work on the others without regards to what you have, your 1st surface definition.
3. eventually worry about the transition between the primaries.

Also, you should to halve your model. Do the left or right since it's symmetrical. Mirror it when done. This halves your problem and insures the left matches the right.

Listen, a long time ago, they realized that you can't have one surface wrap all volumes. They've been trying to define a car fender with one surface since the beginning of CAD and it just doesn't work. That's why you see edges on most b-reps. We've decided that it's best to break up representation into faces and knit them together. I call them primary & transition surfaces.

Focus on the main areas, then blend transitions between these.

joe_dunne

There are several products that are attempting to tackle this problem of creating freeform organic shapes. I might suggest taking a look a Phi.  They are in a closed beta testing of their product.  Certainly their goal is to allow you to create these shapes. beta@phenometry.com

billy2

Maybe this might help. Below is the anatomy of a 3 corner blend from Pro/E that helps identify the composition of a b-rep. I hope this is what this thread is about. The composition strategy for forming complex b-reps.



Above I would classify the cylindrical and spherical faces as primary. With the primaries defined, you add the transition between the primaries.

So what's the best way to build your seat? I don't know, I do know your 2nd attempt will probably be better than your 1st attempt. It's a puzzle, you get to define the pieces and with differing approaches you'll get better edge definitions, robustness and curvature blending. 

It's not that hard to do, and your starting sketches look right to me. You won't get it right the 1st time, but eventually from trials you can do it.

billy2

Like @joe_dunne says, there's currently 2 camps in the world of surfaces: classical & sub-divisional.

Classical, which I do, means the old way, we build with curves and loft surfaces.
Sub divisional, is the new way, means you tug and pull on a b-rep manifold primitive.

Phi is a new sub divisional modeler and truly amazing. Absolutely, go take a look at it.

I went up against t-splines (sub divisional modeler) when designing a mountain bike bottom bracket. He blew my doors off creating something in an afternoon vs. me 2 days. I have to build with curves where he just tugged and pulled.

I did fix his stuff where things were hitting by carving out clearances and knitting in new surfaces. These 2 technologies do compliment one another.

joe_dunne

Interestingly Phi is actually not a SubD modeler.  It's understandable that it is considered one.  Since they are taking similar workflow approach in some ways. They have built a underlying technology that is unique. And because it is not SubD, it allows designers to use curves directly, instead of working with a control cage. 

I love the results of SubD modeling. But the problem with SubD is that it requires a user to use indirect manipulation methods. You manipulate a cage and then the geometry tries to fit into the cage. It's never exact. but it is alway smooth.  So it's definitely very different than NURBS tools. NURBS is one of a meticulous, super controlled method of creating a shape, one patch at a time. The other allows dynamic manipulation of the overall all shape. But it's very hard to control "exactly". 

Potentially Phi achieves a workflow that allows NURBS based thinking (curves), to be used in a more freeform overall shape (SubD).

Joe

billy2

Thanks for the update @joe_dunne. If you're learning organic shapes, Phi is a definite thing to explore. it's different and very easy to learn.