Help needed on creation of auto body features

[CarbonWerkes]

Hi all

Im doing some automotive aerodynamics work, and am using SW to generate my solid models. I have a base chassis (a solid) created. I opted to design this plug as a form without wheel wells, so that I could add fender flares of various profiles later. My expectation was that I would use an extrude cut to create the wheel wells right through the attached solid fender flare so that I dont have a two-sided shape to deal with on the fluid dynamics side of the process (clean solids with no sharp internal angles makes life much easier).

Im having a lot of difficulty generating fender flare shapes. I have tried projecting sketches onto the body to use as a loft edge, but the convolution of the body tends to make the loft distort or even undercut the existing body solid.

So, I guess Im looking for advice on how best to approach a problem like this. Should I use planes and lofts, and knit into a solid? Should I do this as an assembly, where I create an extruded boss and use loft cuts/etc to generate a part for later attachment in the assembly? Are there other/better approaches (have tried sweeps, but the changing profile required makes that not practical)?

Any guidance is greatly appreciated.

 

[Theophilus]

I'd recommend building the body as a surface (or seriese of trimmed, knit surfaces). If the body will have symmetry, take advantage of that and model only what you need.

I don't know how familiar you are with surfacing, but there's a cool tutorial for this sort of thing (using a computer mouse) here:

http://www.productdesignforums.com/index.php?showtopic=230

This will help you get some of the basics under your belt. Otherwise, you're asking some fairly technical modeling questions, somewhat on the order of something that will need to be dealt with on your particular project (instead of in generalities), since modeling an auto body can be quite a complex undertaking.

Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe trumps reason.

 

[CarbonWerkes]

Hi Jeff

Yea, Im a bit past the intro to surfacing stage- cut my teeth on modeling a Porsche 911, and it was no fun going from 2d pics to splines to lofts, iterate 5x until it is right, etc.

Perhaps my inquiry is not generic, but conceptually, Im just wondering if there is a best practices approach. That is, would it generally be better to create a fender flare as a separate part, and then merge it with the body as an assembly (not worrying about that chunk of the flare that is imbedded in the body? Or, is it generally better to try to model a part like this as an integrated face (i.e. a loft or a sweep based on a projected curve out to the fender edge, etc), to be knit into an overall solid?

I can do this no problem as an integrated body (just using 3d splines and lofts), but I wanted to be able to easily change the fenders in the model. So as I said, I basically created a plug with no fenders or wheel wells, and am hoping to just append fenders as needed for eval.

Here is the chassis Im trying to model. As you can see, the rear fender is sculpted and does not have pure circular interface with the body (front is much easier to model).

http://forums.pelicanparts.com/uploads3/930+Right+Side1087174394.jpg

Any thoughts are most appreciated.

Best,

 

[Theophilus]

I think this is still answerable on a more particular basis than simply generally. For example, in the case of the 911 body, joining the fender flares to the rest of the body can cause problems. One thing in particular is trying to use a fillet to blend the collision between fender and fender flare. This becomes a problem where the flare rolls up high on the fender. You've got to be careful anytime a fillet may tend to reverse its direction (interior to exterior fillet)--which could happen in the case with your fender flares.

So if you were modeling a newer body style with the harder edges, I'd use a separate surface--trim and knit. With the older Porche body styles I think you'll find a great deal of difficulty working with the subtle blends between surfaces--something easy to do with physical clay, but quite difficult with constructed surfaces (non-push-pull).

In your case--especially on the rear of the car--you'll probably need to make a kludge of a surface (just the basic form) for your fender flare. Then, cut out areas where your surfaces join. Insert several curves between your surface edges to dictate curvature of the blending surfaces and use the Fill feature to connect things properly again. SW 2007 should have some additional stuff for surfacing as well, especially regarding greater control over the Fill feature.

You've certainly chosen a tough one. ..

Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe trumps reason.

 

[CarbonWerkes]

Hi Jeff

Thanks for your thoughts on this. Yea, the 911 is a very difficult chassis to model- the front headlight tunnels, and the rear quarter panels and fenders do not lend themselves to simple lofts or extrusions. One major challenge for me is that this model must export cleanly (no gaps or sharp angles) so that it can be meshed for later analysis. Im not an artist, but I have used products like Lightwave and 3DS which seem to have much stronger lofting capabilities, as well as the sort of clay-ish push/pull deforms. I know the underlying technologies are different here, but seeing that SW can generate splines based on projection, it would seem possible to use that capability to generate a matrix that could be deformed, yielding a smooth lofted surface. Maybe in 2007.

Anyway, my core challenge here is a bit more horrible, in that I need to be able to bolt on different fenders and wings- while retaining smooth interfaces between the objects (for later meshing). I did have some luck using a projected spline onto the rear quarterpanel for the interface between fender and body, and then a sketch on a plane defining the outer edge of the fender (parallel with the wheel) and lofting. But, getting to a solid from that is difficult. Sweeping through a series of profiles seems to be the best bet, so long as the sweep intersects the body completely and at a shallow angle. Not impossible- just takes lots of time.

Was just hoping that I could use one of the more obscure surfacing techniques like Deform here; again, not a CAD artist, just doing the foundation work for the later stage.

Best,

 

[Theophilus]

I was trying to think of where I saw a tutorial on creating a bottle (as in for washing detergent) using SW surfaces. I believe I tracked it down:

http://www.dimontegroup.com/Tutorials.htm

You'll need to search where this particular one is, but I think this will help the most for what you're doing with the car bodies--lots of removing/cleaning of surfaces with fills, etc. Don't download/search the stuff until after 5:00 PM, CST, since they're trying to run a business with their site, too.

Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe trumps reason.

 

[gmarken]

CarbonWerkes,
Is it possible to get a copy of your 911 model? I am a member of PCA and own a '69 911E. I would like to use the model in our chapter news letter (Metro NY).