Z32 Rear Upright 3D Scan

[Stingy49]

Hey All,

I took some time this weekend and tried my best to scan in an aluminum Z32 rear upright/knuckle. I used Recap by Autodesk and my dslr to generate the model. I scaled the model by measuring the parallel surfaces on one of the bushing locations.

Basically the plan is to scan in a s14 subframe before I swap one in to my s13. With the knuckle/upright and subframe pickup points scanned (taking care of the difficult to measure points in 3d space) I can model up the suspension arms and have an "accuracte" model of the rear suspension. Then I can try various arms lengths to my heart's content and see the effects on bump toe and such. I haven't actually made a traditional model yet but I will post it on here once I do (probably sometime during my winter break).

I'm not a mechanical engineer by any means so if people have suggestions or requests I'd love to hear them! Also, if this thread needs to be moved feel free to do so.

Here is the link to the files on google drive. If anyone would like it in a different format please let me know.

https://drive.google.com/drive/folde...xY?usp=sharing

Edit 1: Including a picture to show the resolution of the model. Just over 500k faces at full resolution.



Edit 2: I re-scaled the model based off of the ID of one of the holes. My real world measurements are now matching up much more closely with the model measurements. The 14.05mm vs 14.357mm I was talking about below now is 14.05mm real world and just about 14.065mm in the model.

-Derek

[Def]

That's cool stuff.

Did you spot check some other areas to make sure it's dimensionally accurate? Generating models from pictures is really cool tech, basically bypassed professional industry and went straight to consumers almost immediately upon availability.

[Stingy49]

I honestly hadn't yet. I just went and checked the thickness up near the caliper mounting holes and measured 14.05mm with my calipers and I'm getting 14.357mm on the model. Keep in mind it's kind of tricky to measure points directly opposing each other cause I have to eyeball two points that look about right in the software. It's kind of tough to pick points to use as the reference (when setting the initial scale) because the mesh models don't really have perfectly flat surfaces like the real deal. My plan was to make a traditional model in fusion360 and have the mesh model as a reference to get angles and hole centers right.

I completely agree! Autodesk has amazing student support so I can use the pro software and their cloud computing services for free. Saves a bunch of time on high res models like this.

[gills]

Very cool, Stingy.

I have access to the entire professional Autodesk Product Design and Manufacturing Collection and I had no idea about Recap. Autodesk has so much stuff and they buy software companies every year that it's hard to keep up with their offerings.

The caliper mounting holes center-center distance is 114mm if you want to check that as well. I'm measuring 116mm from your model.

Why use Fusion 360 instead of Inventor? Fusion 360 is good with advanced surface modeling and the fact that it's cloud based, but from what I can tell that's its only advantage if you have access to Autodesk's entire suite. Managing sketches, datums, geometry projection, function driven dimensions (not possible in Fusion), multi-solid part modeling for associated assembly creation (what you'll want to do when you model in sub-frame and suspension arms), etc... are all much better in Inventor.

With that said, I've been wanting to do this for quite some time. I'll have to read up on the functionality Recap and how you actually reference stuff. Importing the STL into Inventor and the origin planes aren't aligned to any surface. Is it possible to have more control over reference planes when in Recap?

[Stingy49]

Answering out of order:

I had honestly picked fusion360 cause guys like NYCCNC on YouTube were using it and had good tutorials. The improved assembly options would certainly be nice as I have struggled with those in the past with fusion. I'll give it a try today if I can fit both on my laptop (time for a bigger SSD).

Was that 116mm dimension measured on my re-uploaded stl? The one actually called z32 instead of 300zx? I rescaled the stl last night and re-uploaded it. Just compare the file creation times and I'm sure you'll be able to tell which is newer.

I'll take a look at the origin planes today. I get what you are saying cause aligning the stl in fusion took me a few minutes of 0.5* angle changes and looking at the part from a bunch of side views.

Yeah this 3d scanning stuff is super neat but scaling the models is always tricky. I wonder if I included a cube of a known size in the frame and scaled off of that...? Like I was saying to Def, the other struggle is picking two directly opposing points on parallel surfaces to apply the scaling to. The cube would give me nice corners to use as the scaling points. I would love some suggestions here.

-Derek

[Stingy49]

I printed out a test piece to check how well it matches up to the real deal. Looks pretty good so far.

[gills]

Yea, if you're going to do anything with assemblies, use Inventor. If you're looking to make organic shapes and surfaces, use Fusion360.

So yea, I d/l'd both but didn't check file name "Z32..." That one is closer to 114mm (~114.4) so it's def more accurate.

As for the planes, etc., if there's someway you can set, for instance, the hub mounting surface as a reference plane it will make life easier when you import it into Inventor/Fusion.

So seeing how's there's a gazillion surfaces per face, they average out to flat wherever actual flat surfaces are supposed to be. If you "create a plane using 3 points" where a flat surface is and create another one on a surface that you know is offset, but parallel (ie. caliper mounting ear surface and hub mounting surface), you can get something real close (about 0.1 degrees of each other). Measuring that offset on the actual upright should be easy enough though, but it's reassuring to know when you create planes on all the bushing/pivot surfaces, the angles will be close to the real thing.

You can then model extrusions for the bushings/pivots from those created planes the thickness of each bushing. Then create an accurate dummy model to constrain to and run kinematic analysis for things like bump steer, camber gain, etc. Just remember that you'll have to make the pivot constraints spherical/ball so the assembly will actually move.

Looking forward to your subframe scan!

[Stingy49]

Alright so I downloaded Inventor and I'll learn it while I model up this part. Having used Solidworks and Fusion previously this looks pretty straightforward.

I dropped the mesh down to 50% of the original after my computer was lagging real bad on the original stl. Recap does pretty nice adaptive mesh scaling so it'll trim heavily on the mostly flat surfaces and maintain detail on the edges. The new stl also has the wheel bearing mounting surface aligned to one of the origin faces.

I went ahead and made two faces using the 3 point plane command and the results look great! Only 0.04* unparrallel.



I think I'll just try and midplane each bushing location and do "floating" sketches/extrusions like you suggested. For the time being I'll just fix all of the floating extrusions relative to each other (or maybe it does that by default) since that is all I'll need for the kinematic model.

I'll probably get around to scanning the subframe pickup points in two weeks while I'm waiting around for my one final. Lighting is gonna be interesting in the garage and I can't have moving light sources. Maybe it's time to go run by Harbor Freight and get some stuff.

So far I'm pleasantly surprised with how well all of the measurements are turning out. I did not expect this level of accuracy with my quick setup and photo session. The possibilities are pretty sweet. Between this and the cost of 3D printers nowadays prototyping is getting super easy for us home gamers.

If anyone knows the lengths of the various control arms that would save me some time. I think the ruca is around 12.5" and the tension rod around 8"?

Time to try my hand at modeling this beauty...

-Derek

[gills]

Excellent! The 50% mesh helps a lot. Where were you a few months ago when I was designing a rear BBK! lol. All I modeled were the caliper mounting ears.
(Shameless plug: it's just about ready for sale if anyone is interested in a rear Wilwood BBK that doesn't need to chop off the caliper mounting ears. 12.2" x 0.81" rotors).

You don't even need to link the pivots together since it's the same part file if you want it to be very simple. When you create your assembly file, the floating pivots will be treated as a single part and move in unison.

As for the links, there's definitely information in here. Search user "Jason M" as he did a lot of suspension analysis on his own car that he is/was very competitive with.

The only issue I see with this is that Autodesk/Inventor doesn't have a native kinematic/dynamic analysis environment that I can tell. I don't understand how they couldn't. Pro-E has mechanism analysis which I had used extensively in school and I'm sure Solidworks has something as well. Otherwise you'll have to take a manual approach and move the assembly in increments and note the angular changes in the camber and toe planes and plot it in excel. If you have access to Solidworks and it definitely has a kinematic/dynamic environment, you can just do all this in Solidworks.

How many photos did you end up taking for this?

EDIT: Inventor has "Dynamic Simulation" under Environments tab in assembly.

[Stingy49]

Lol someday my 240 will be built enough to need a bbk. I should start a build thread...

Awesome. That was the sense I got when I started modeling it but it's good to hear it confirmed. My first attempt at it is up in that shared folder now btw.

I'll have to find those threads again. I remember reading them a while ago. I hope he sees this thread eventually, it would be cool to hear his opinion on this stuff. I'll definitely compare my data to his once it's all done.

So what sort of output does the dynamic simulation environment give? Equations of motions or autogenerated tables of data? Either would be super helpful.

I only took 58 photos total at 18 megapixels. I basically put my camera on a tripod and stepped around the part in roughly 10* increments. I repeated it once more at a lower height an then handheld took like 4-5 images of the bottom of the part to get the ball joint mounting surface. There are some parts of the model that are noticably a little lower resolution so if I actually took my time and did passes at 3-4 heights instead of just two it would come out even better. I think my student account is limited to 100 photos though.

For the s13 subframe pickups I'm obviously not going to circle the subframe (once I get an s14 subframe I will scan it outside the car). For the s13 subframe my plan is to just take photos from a range of angles from the wheel well. I've done buildings and stuff that way (not walking around them) and the faces I actually get in my photos turn out great.

If you have any parts you want me to run on their cloud just let me know.

I'm thinking it would also be cool to scan in my center console cavity (where the stereo goes) so I can make a 240 double din touchscreen mount. I have a raspberry pi in there so I can tune my megasquirt/show gauges but the screen is always kind of lopsided and sitting funny.

-Derek

[gills]

It should be able to provide forces, accelerations, velocities, and position at any user defined point on the mechanism if it's truly "dynamic."

Typically you'll define an input force/torque to drive the mechanism how you want over a certain period of time. Then you should be able to pick a point or a few (or perhaps plane) and monitor their positions relative to a reference origin/plane with respect to the time.

Looking briefly at Inventors Dynamic Simulation it seems like it's limited compared to what I used in ProE 5 years ago, but I think should be able to get the job done for what we're looking for.

I already d/l'd your model with the pivot extrusions this morning. You're on the right track.

I also have already installed Recap Pro on my machine. Looking forward to testing something out. Should do the front upright now as well!

I like the idea on getting the S13 pickup points. I'm thinking you'll have to make sure the car is level when you do this so you'll be sure to get the proper orientation of the Z32 upright when you assemble everything in CAD.

[Stingy49]

Gotcha. I found the dynamic simulation course on their design academy so I'll work through that until I think I've got enough knowledge to make the simulation.

Glad to hear it looks alright so far. I'll probably have to change the thickness of the joints around but that's easy.

Yeah that was going to be the natural progression of this project lol. I started with the rear end because I had the upright in my hand and my rear end is tail happy right now. Probably due to way to much camber but I'll fix that soon.

Maybe I'm missing something but with all the arms in place won't the upright self align relative to the subframe? I guess keeping track of the subframe/entire assembly relative to the ground would be important so we know how the movement of the wheel bearing plane corresponds to toe and camber (since those are referenced to the ground). When I scan in the subframe it will definitely pick up the ground as well. Then we could set our angle relative to the ground based on our unique ride heights.

I'm itching to model the rest of the links lol. Maybe I'll pull my rear end apart sooner rather than later. Senior project is telling me no though

[gills]

The subframe pickup points will fix the upright to an orientation, but like you said, you won't know how it sits relative to a level ground plane where the tire sits and the planes/points you're monitoring will be skewed.

[2_Liter_Turbo]

I uploaded an S14 rear subframe and linked it on here at some point. Very cool about the knuckle, thanks for sharing!

[Stingy49]

2_Liter_Turbo, you uploaded a model of one? That would be a cool starting point. Finals have me swamped so I won't get to taking apart my rear end until sometime next week.

I'm happy to share! I've learned so much reading the various threads on here that I am excited to finally be able to contribute meaningfully.