How to approach modeling a complex shape

roger_smetaniuk

Currently I have been getting comfortable with onshape by modeling up the race car. I am having trouble coming up with a plan of attack for modeling the rear engine cover as it has a lot of different curves, angles and shapes usually all flowing into one another.

Anybody have any suggestions? Currently I think I will have to make up several different slices and try and loft it all together but I find loft can be hit or miss depending on the complexity of the shape.

MichaelPascoe

The Loft approach would be perfect for this. For complicated lofts, you can focus on one surface at a time to make it easier. Bounding surfaces can be knit back together with the Enclose feature to create a solid part.

The key to making a complex loft work is:

1. Match connections (You can match several connections. Once the first two connection points are selected, minimize that connection to be able to start a new connection.)
2. Show iso curves to see which connections need to be adjusted

Other things that can help but it will depend on the level of control you need:

• End conditions
• Guides and guide conditions
• Path

roger_smetaniuk

The only problem I have with the lofts is not knowing the dimension of the slices as they would be difficult to measure off the bodywork. I thought I had found a way over the weekend using projected curves but after all that work looks like Onshape doesn't have the HP to figure out a large curved section. 

steve_shubin

@roger_smetaniuk said:

The only problem I have with the lofts is not knowing the dimension of the slices as they would be difficult to measure off the bodywork.

DIFFICULT TO MEASURE

Here in the forum, you will find posts by @billy2 who has some kind of a scanner that attaches to either his computer or iPad or iPhone or similar device. And he is able to make parts for his motorcycles off of the scans that he brings into Onshape, But I think the scanner that @billy2 has is something that’s no longer in production

Well I happened upon a video by someone reviewing a scanner app that works with one of the newer iPhones

https://www.youtube.com/watch?app=desktop&v=dVCbZmIXoTI

I looked at the app in the iPhone App Store

https://apps.apple.com/us/app/em3d-ethan-makes-3d-scanner/id1546149822

Read a review about the app by Bryson H. He said the app was good enough for engineering. And that by using the apps STL output, he can bring a scan into CAD, and make slices (profiles) from that

Here in the forum, I’ve also heard people mention a program called meshmixer which is free and has been used as an intermediary program WHEN NEEDED. From there, you should be able to get it into Onshape

BUT — you likely can export an STL file directly from the scanner app, and then bring that STL into Onshape without even having to use meshmixer as an intermediary

There are options to purchase within this scanner app. It looks like at minimum, you would have to buy the STL export feature in order to get a scan into Onshape.

A sidenote — I always try and research who it is that makes an app before I install it on my iPhone or computer. When you get to the App Store, there will be a link to the developer site for the scanner program. Go there and under the three horizontal lines (the hamburger), tap ABOUT and then scroll down and take a look at the picture of the author of that program. All I can say is YIKES. Someone that young making an app like that. WOW

You could visit the kids YouTube site and even watch him showing how to do some basic python programming

I have not looked at any other scanner reviews. That is something you might want to do before making any purchase

dirk_van_der_vaart

It looks like your Part Studio has more than 360 features, that's not really a good practice.
There are a lot of video's and webinar's to see and to learn from.
Like this one
https://learn.onshape.com/courses/surfaces-and-curves-in-onshape

john_mcclary

Loft will likely be the only way to achieve your shape. 

GWS50

I have used software called Skanect and an xBox Kinnect in the past which is a cheap way to get a reasonable scan. I got an old kinnect device from ebay for about £20.
The Structure Sense for ipad is not too bad either but more expensive.

GWS50

P.s. Scanning is a 'Dark Art' and needs patience and perseverance. 

roger_smetaniuk

Ended up getting it about 90% accurate using the projected curves and surfaces. 

roger_smetaniuk

dirk_van_der_vaart said:

It looks like your Part Studio has more than 360 features, that's not really a good practice.
There are a lot of video's and webinar's to see and to learn from.
Like this one
https://learn.onshape.com/courses/surfaces-and-curves-in-onshape

Yes I am noticing it slow down a lot now. I am just not that fluent with doing different parts studios then into an assembly. Also a lot of the parts require other parts for locations etc. So would you normally copy over the parts you need into another studio just to design the next part?

S1mon

Good practice would be to have a top level part studio which defines the overall sizes/locations of key subassemblies in a very schematic way, and then derive that into part studios to create those subassembly parts. That top level might just be sketches and no solid/surface bodies. For instance, the rear wing looks like it has some attachment points to the frame/body but otherwise all the parts within the rear wing are independent of the rest of the car. I would have a few sketches at that top level part studio to define the interface, and perhaps the overall envelope of the rear wing, but all the details of the rear wing parts belong in another part studio. Similarly, there's no reason to model the wheels in this part studio. The top level would have the wheel base/track and perhaps the mounting pattern and nominal tire diameters.

edward_petrillo

To elaborate a bit further on @S1mon's excellent advice, carefully choose the origin of your top level (I call it "Master") part studio in relation to the structure of the entire car.  Derive sketches from the Master into your subordinate parts studios and maintain the position of the origin in those studios, in your top level assembly, and in any subassemblies. Keeping the origin consistent makes populating your assemblies a breeze- the parts snap into position when inserted.  The common origin also facilitates editing in context.

S1mon

@edward_petrillo

For all the major body parts I would very strongly agree with that advice. For things like the wheels or steering wheel, it probably makes sense to have those part studios' origins set so that the axis of rotation is at the intersection of two of the default planes. This means that you'll need to derive the mounting pattern from the top level and transform it, or perhaps derive the mounting pattern in the top level master from the wheel and steering wheel part studios.

billy2

@roger_smetaniuk

They still make it: https://structure.io/structure-sensor-pro


I have a really old version and need to update it. For the cost, it works well. Does it work with Onshape? Yep, I've been using it ever since Onshape has supported meshes and Onshape has it working well.

How do you get started? Follow every suggestion above. Aligning meshes up will be problematic and establishing an origin is key.

I don't use derived partstudio's and prefer to run everything through an assembly & incontext. It's a poison you get to chose.

You won't have one mesh due to density issues and will be aligning different meshes with different resolutions. If you create a layout sketch you can attach different meshes to the layout sketch keeping everything organized.

Don't forget about pictures. For the overall shape, I'd use an image. Images are a pain due to parallax, but you'll figure it out. Something this long you'll probably need a front image and a back image. I think there would be too much distortion for one image and the entire car length.

You have to learn surfacing, there's no extrude, fillet, fillet, fillet, blah, blah, blah.

Think about your primary shapes, like the car body, then the finer shapes, like a wheel well. With onshape you'll control primary (car body) & secondary  (wheel well) surfaces. Then, you'll transition between the primary & secondary with a tertiary surface. Don't watch videos about sub-divisional surfacing, Onshape doesn't work that way. Creating a primary & secondary surfaces properly so it'll accept a smooth tertiary surface is the art of engineering a body shape.

For your primary surface, your construction curves are not the edges of the surface you're looking for. Create the shape and then trim back to form your wanted edges. This is an IGES 144 which is old school from the '80s. Read about it, it's extremely simple.

https://cad.onshape.com/documents/7fb41efc3e90820ffcb95eca/w/8538cad1400bf7739a959cb5/e/8195c46701f990d168312ea4

You have to master the workflow above, many have and you can do it.

You're first attempt won't look that good, but your 5th or 6th will look alot better. The best time to create a body for your car is Saturday morning between the 1st & 2nd cup of coffee.

The nice thing about onshape is that it's parametric so there's no reason you can't build a control skeleton, attach your surface curves and create shapes that'll update with your design intent. You can change your wheel base and have the body automatically update.

Is this doable? yep, there's a lot guys here in this forum that can do this. With time you can do it too, but it takes time.