Trouble with rail curves, trying to achieve loft in solidworks equivalent

[Anonymous]

Hi everyone, 

I'm trying to recreate what is being done in this video (https://youtu.be/u8gdXDwwL9M?t=920) in Alias. Essentially a cockpit shape is created through the loft command in solidworks by selecting some curves as the profiles (generation curve in Alias) and one curve as the guide (rail curve in Alias). The closest I've gotten is this:

 

Very obvious problems in the shape can be seen in the start and end of the rail sweep. Another problem is that the screenshot is a "scaled down" version of what we're actually trying to do. In the actual design of our car we intend on have the profile be an imported .csv file that give coordinates of a wingfoil shape and this results in 61 span curves. So even in the simple one we have issues but in the full scale it simply refuses to make the rail sweep because it would result in exceeding the maximum surface spans. Any ideas on how to rebuild a 61 span curve without destroy the shape? With rebuild curve going down to 20 results in a super "blocky" curve. Sorry for the long post by tl;dr:

1) How can we make a proper cockpit rail sweep without the errors in the screenshot?

2) When we figure out how to rail properly how can we properly use a set of coordinates to make a low-span curve in Alias? Using a import CSV plugin results in 50+ span curves that we can't figure out how to rebuild.

I've been bashing my head at this for hours so I'd really appreciate any help! Thanks!

[Anonymous]

So using Rebuild Curve I got an imported airfoil shape down to 13 spans but it looks super ugly 😕

On the rail side of things, I figure out how to make it a bit better by making sure all my intersections were on the same plane but it still looks messed up at the edges:

[duaxiong]

You can use Explicit Control in the Birail tool to lighten your spans, but imported curves will probably not be so great for building, so I would just use them as guides and build new Alias-native curves for constructing your Birail.

...or if you have more flexibility in your desired shape, just use a Plane and start pulling on some CVs; a shape like that should take less than a minute.

[Anonymous]

So the thing is the first screenshot is done without using an imported curve. I believe all the curves used in that birail were less than two or three span and only a few CVs. Is there fundamentally something wrong with the way I'm selecting my generation/guide curves? My result is incredibly close to what I want, just distorted in the front and back for some reason....

Forgive my ignorance but I'm also having trouble understanding why Alias is having so much trouble in doing what Solidworks can do super easily. Isn't Alias far superior for surfacing?

[Anonymous]

Alias works differently than SolidWorks does. You cannot completely copy a workflow to another software and expect the same or better results. Rather you have to adapt a workflow to use the potential of another software. I know, you transferred the loft command to the monorail command, but that obviously isn´t enough.

Things that could help building that surface are:

• Splitting the guide curves into different curves where each one of these curves follows it´s own kind of flow (constant, accelerating or decelerating)
• Connecting different curves to fit your purpose of continuity
• Rather building just one half of the surface (90°) and mirror the other half (to make it your 180° segment) than completely creating all 180° of the surface in one.

I hope that helps a little bit with creating. I can actually just assume, what could be helpful

[Anonymous]

Hi there,

did you link to the right video in your first post? I cant see anything like a cockpit in there. Its about an solar car, pretty easy to achieve. But it does not look like the thing you seem to be after...

Basicly there is no problem to use any importet curve in Alias. It depends on how close you want to stay on your input curves. "Bad" input geometry will result in bad model-quality, except you allow the surfaces not to stay 100% in the input curves. Then you will be able to create smooth models even out of crappy curves.

It might sound hard, but it seems you used the rail tool in a totally wrong way.

Sadly i dont have the time atm to write a detailed "manual".

Maybe you could place a screenshot of the shape you want to model (couse i couldnt find it in the video).

Tip, dont let surface corners run into 1 singe point. This almost allways gives bad geometry. It only works for revolves. Try to use Gen1 and Gen2 as rails, forget Gen3 and use Rail1 as profile. Separate the start and endpoints of the new rails and put the ends of the profile curve at the startpoints of your new rails. You can add as much new profile curves as you want along the rails. But rather keep the input geometry in low complexity. Results get better that way.

I know a little SWX and Rhino, too. And i think SWX also will produce funny things when using the loft in the way u tried to use it in Alias. But i will have to test it.

But i am totally sure that Alias is "far superior for surfacing". 🙂

Hope this helps for the Moment...

Regards

[Anonymous]

Yea sorry I wasn't too clear on what I was actually trying to make. If you go to 15:25 in the video (https://youtu.be/u8gdXDwwL9M?t=925) you'll see the exact command for the cockpit loft being given and the surface being highlighted is in a yellowish color. For a solar car body the only main components are really your top body, your wheel and driver fairings, and the cockpit. The cockpit is the protrusion from the top plane in that video, better seen in this screenshot of Georgia Tech's new car (I circled the cockpit area): 

So I tried what you said with the Generations and the Rails and it said "Generation curve has zero length between rail intersections. Cannot construct surface." I think it might be a little difficult to see which curve is which in my attempt where it almost came out right so here's a screenshot that more clearly explans what is what: 

[duaxiong]

Surface patches are four-sided.  The shape you are trying to build does not have four obvious sides, so we will need to devise a way to build that shape using four sided patches.  The easiest way is to Trim the four-sided patch to give you something that is not four-sided.  Fortunately, you have the body of the car with which we can Intersect the canopy surface.

Below is just one method; the fastest and easiest, I think.  Everything is done by directly moving CVs, no Birail or any other surface construction tool.

First we start with the body;  It is abbreviated here, but is a simple default 3x3 Plane shaped by moving some CVs.

Next we build another 3x3 Plane for the canopy surface.

Move CVs to shape it.  You may need to add some Patch Precision to it so that you can better see its shape.

More shaping by moving CVs; this time in the side view.

Shaping in plan view.  If you need a more complex shape, you can increase Degree or even add Spans for more CVs to move around.

A few final tweaks, and it is basically finished.  

As you can see, the canopy surface extends beyond the body surface.  You can trim them where the intersect or you can also add a fillet here if you need.

[Anonymous]

Thanks so much for taking the time to write that out! While I have used a sphere primitive to create a general cockpit shape previously the only issue is now that we're trying to optimize some aerodynamic things, the cockpit profile on the top body is defined quite strictly by imported .csv files with curve coordinates which is why I've been trying to get the rail to work. Any ideas on how to make a cockpit from an imported curve?

[duaxiong]

Personally, I would not.  The chances of those imported curves being usable as is, is very low.  

If you absolutely MUST maintain those profiles, then you will likely need to rebuild them first.  The shape you are trying to build is rather complex in that it goes from a relatively large radius down to a pinch at the tips; I doubt that the rail tools will be able to interpolate this properly and you will end up having to split the canopy up into multiple patches.

What I would do is the method above, using those imported curves as guides to shape the canopy, increasing the CV count as necessary...concentrating more on making the surface nicely shaped and clean, even if it means deviating a bit from the guides.

[Anonymous]

I see what you're saying, I tried playing with said primitive plane and its extremely difficult/unwieldy to try to shape it to a curve but I guess we can do that as a backup. It's actually not difficult but more-so we typically iterate with super minute changes in the curve profiles so it'd just be a bit more convienient with an imported curve. 

I tried doing the rails in sections and had a slightly better result but it appears the sharp corners on both ends of the cockpits are what are causing such issues for the rail command. Anyone know if it's possible to achieve tight corner surfacing in Alias? I know I sound like a broken clock here but I feel like if it's done so easily in Solidworks it should be atleast doable in Alias no? 

[duaxiong]

I'm going to guess that the person running Solidworks in that video probably has more experience in Solidworks than you have in Alias.

It is doable in Alias...and it is easy.  I think you just don't have enough experience yet to be able to do it.

If you can upload the curves, maybe I or someone here can try it for you.

[Anonymous]

Yup I definitely think this is the case! I'd very much appreciate if you could try making the cockpit surface with the attached file. The only curve that really matters is the airfoil shape in the XY Plane, the other two were somewhat arbitrary but it'd be awesome if you could form the surface with the curves currently in the model. 

Figuring out the cockpit would be really dope because it's one of the last major struggles we're having with making our car in Alias (not true we're also stuck on some fillets but that's for another thread 😛 ) Thanks for the help so far everyone!

File: https://www.dropbox.com/s/cmiq8ssz8t0m1ar/AirfoilAttemptsCockpit.wire?dl=0 

(apparently .wire isn't a valid extension for uploading files to this forum?)

[Anonymous]

..which is very sick (the wire ext phenomenon)...

Thank you for the crvs,....

[Anonymous]

You provided some really particular curves i would say, keeping close to this geometry would end up in a non symmetric cockpit with a windshield whiper pocket in front and a tube like ending. Also the curves itself are not smooth...(the "mohawks" in the second shot should be nice and smooth, not that bumpy)

Is that what you want? This would be possible, but i am afraid this is not to be handled quickly.

See screenshots...

Id rather believe your import tolerance settings for the curves was too low. Could you send the .csv? How did you import this data?

Kind regards...

[Anonymous]

Hi! Thanks for looking at the curve files, the imported curve on the XY plane's csv file is here: https://www.dropbox.com/s/6iujnrbzseseqw0/789.csv?dl=0

And I imported it with the use of this plugin: https://apps.autodesk.com/ALIAS/en/Detail/Index?id=2206152797041147982&appLang=en&os=Win32_64

With regards to the curves, sorry I trimmed things and detached things and forgot to put them back together perfectly. The curve that matters the most is the imported airfoil curve and the curve in the ZX plane we made kind of arbitrarily but in the actual design that curve will be made to properly fit our chassis, I guess for now you could make it however you want. Same with the curve in YZ plane, I just made in a random spot to be the generation curve. 

[Anonymous]

...lol

Anyone know how I can make a cockpit shape with an imported curve? 

[Anonymous]

Well the importet crv looks pretty exact. But due to the csv data it is a polyline with straight sections, you need to rebuild it to get it smooth. Or rather create an own crv close to the csv data.

You have to realize that this csv provides points, not crvs. The crvs are created by the plugin. Its simply "painting by numbers". So you dont actually import crvs, which would be much easier.

You have to create your crvs out of a pointed line.

What about the revolve way i sent you via pm? Pull some CVs ...

As soon as i can find some minutes i will do an attempt on this cockpit. Whats your deadline? Can you send the top surface of the car?

ciao for now...

[Anonymous]

No rush! We have atleast the next two weeks to atleast have an idea of how to build most of the car in Alias for the time being. I totally understand you're very busy and I appreciate you taking the time to do this very much! Let me know when you get an attempt to try the cockpit. As far as importing the curves goes the instructions are on the plugins website so let me know how the attempt goes or if it turns out well.

[systembolaget]

Hej vdesai2014,

as the others have said, these kinds of shapes are why Alias is used in automotive, aerospace, public transport and high-speed rail.

The thing with having to work to externally sourced data (point clouds, meshes or non-NURBS curves) is that one needs to either re-build that data (you'd have to do that for ICEM, Alias, Rhino - you name it) or fit new curves in the right places that approximate the polygonal curves (in your case) to the desired tolerance. If you try to copy a workflow from Creo or Solidworks to Alias or other surface modellers, you will fail, because the difference is substantial. It's far easier to discuss this face to face or via TeamViewer screen-sharing when you're a novice user. Maybe ask some good NURBSers to go through the existing demarcations your shapes must be constrained to.

Good luck with your project!