Batmobile: ground fx and fender flare

In the last episode, we joined the fender and the cowl with a Boundary surface. In this episode we will attempt to make it all the way through without using a word that rhymes with “cowed”.

Why is it that this and most car tutorials that you see start at the front and build to the back? I don’t know.

In the immortal words of Primus;

Is there Heaven?

Is there Hell?

Is that Tuna Melt

That I smell? C’mon!

So what are we gonna model today?

After the Boundary surface joining the fender and the cowl, I split the freaking thing in half. Why? Because that’s what I did. The cowl was easy to build about the center plane, and less easy to build only half of it.

Here’s a great tip that Ed Eaton turned us all on to years ago: If you split something (symmetrical) in half (along the plane of symmetry) and then later mirror it, you don’t get the split down the middle. When you say it out loud, it sounds kinda stupid, but when you do it, it seems cooler. Just remember that next time you work on something symmetrical, and it is more work to model half of something than all of it. You can use a plane to do a Trim (on a surface) or a Cut With Surface (on a solid).

Ok, next we start working with bodies. Most of the car body turns out to be a single surface body, but some of the moving parts will be separate surface bodies. Like the jet rotor. The central rotor is just a revolved surface. Then the fan blades are simple lofts. When making a “looks like” model that doesn’t have to be very accurate, as long as you have something that looks complex, sometimes you can get away with a lack of accuracy. That’s the situation we have here. You can call it “fake” if you like. I call it not spending an entire weekend on detail for a project you’re not getting paid for.

Offset plane. Copy and rotate sketch slightly. Loft. Pattern Body. Apply materials. Enjoy your weekend.

Backpedalling a little, here’s a tip for that nose in the center of the rotor. To get really smooth looking shapes that aren’t all herky-jerky, use splines, and pay attention to the details.

This is a two point spline. Notice I changed the color of the curvature comb (Tools, Options, Colors, Temporary Graphics Shaded) because the default yellow on white is nearly invisible, and added the cap to the curvature comb (Tools, Options, Sketch, Show Curvature Comb Bounding Curve) because it just makes it easier to look at.

The two points of the spline start at the center line of the rotor, and end at the OD. At the CL, the handle is given a vertical relation, and at the OD, the handle is made horizontal. To get the handles on a virgin spline, just select the spline, then select the diamond on the spline handle to change the angle. The curvature comb can be shown via the RMB. When the curvature comb tapers to nothing on the right, it means that the spline is nearly a straight line. Ideally, I would have liked the curvature comb on the left end to end vertically, but it didn’t. That kind of thing can be hard to control. The slope of the curvature comb signifies the rate of change of curvature. If the rate of change of curvature is continuous but changes abruptly across the center of revolution, well, frankly, that’s something that you’ve got to have a really good imagination to see. I don’t think I could tell. If you have a really really sensitive eye that’s offended by abrupt changes in the rate of change of curvature, SolidWorks doesn’t have great tools to accommodate you. You could make the argument that they really really need something like that, but frankly, I wish they would work on other things like flipping connectors or stuff like that. With practice you can tell when the curvature changes abruptly, but the rate of change of curvature is more subtle.

Anyway.

The ground effects around the front of the fender were tough. This is mainly because of quirks in the Ruled surface tool. Don’t get me wrong, I love the Ruled surface. Where would we be without it?!? But it is quirky, and sensitive, and often gives results you wouldn’t expect or want.

The first ruled surface creates a flat surface out from the bottom edges of the fender. Selecting the type can be confusing. “Perpendicular to Vector” means perpendicular to the normal vector from a plane. Wha??? Yeah, it does. So it asks for a vector, and you select a plane. The secret knowledge required to make this work is that each plane has a “normal vector”, which is really just a perpendicular direction. Nowhere in the SW documentation that I am aware of do they make a discussion about plane or face normals or vectors in general. The people who do the programming are geometrical mathematicians, and to a mathematician, all planes have normals, and normals are vectors, so vectors and planes are interchangeable, right? Whatever. You might be better off to just click through the choices and see which one gives you what you want. Just like the new Plane interface.

Next, I used the edge of the first ruled surface to make a second ruled surface, but this one at an angle.

Ruled surfaces have curvature in only one direction. Remember the U-V directions you read about in the SolidWorks Surfacing Bible? On a ruled surface, one of those directions always has straight lines, and the other direction can be any curve. Ruled surfaces can save you a lot of time, or they can be very frustrating. Getting the angle to go the right direction and the surface to go the right direction involve using the Alternate Side button (edge in selection box must be selected) in combination with the arrows button (next to Top Plane above). Each angled ruled surface can go in one of 4 directions, so you have to get used to using these options.

Next is the wheel flare. These can be difficult on cars like the 911 or 350Z, where the flare is really a continuous part of the fender, but on this car, there was no flare aside from a small, very controlled one. So the first thing is to trim it out of the fender. Easy enough. Notice how it has also trimmed out the ground effects flare. We’ll patch that up later.

Next is a small flare that comes out parallel to the axis of the wheel. I used Perpendicular To Vector, with the Top plane as the vector. This is the same settings as the first ruled surface shown above.

Then a small return that looks like a flat face on the outside, giving the flare some depth. This one uses the Normal To Surface option.

Finally the angled return

And after a series of trims and fillets, you get the final product:

Alright. So now you know more about ruled surfaces. Maybe some day SolidWorks will fix them up real nice so you can do stuff like this without swearing.

Next time we will finish the main body and the cockpit.