Designs on software v/s practical stuffs

[Marvel]

Hello,
Its been a long time I was wondering; how can I actually come to a conclusion (economically*)that the stuffs I am doing on software and the ones I am doing while actually manufacturing are close enough(may be not exactly...manufacturing errors!)
For example,
how can I conclude that the position of suspension brackets while actually mounting it on the chassis is slightly the same that was decided on software. There may be some deviation but this will deviate many other parameters. For instance, there may be some deviation from initially decided static camber suppose -2degree to somewhere -2.1 or even -3degrees or 0degree?
This will further change some other characteristics like the camber again, contact patch...etc...etc...
I understand this all depends on manufacturing processes and proper care is to be taken but a slight deviation of 2-5mm can change many parameters.
economically* - without any sensors etc...
(I am myself confused...but I hope my words are clear enough to understand what I want to say... )

[Marvel]

Hello,
Its been a long time I was wondering; how can I actually come to a conclusion (economically*)that the stuffs I am doing on software and the ones I am doing while actually manufacturing are close enough(may be not exactly...manufacturing errors!)
For example,
how can I conclude that the position of suspension brackets while actually mounting it on the chassis is slightly the same that was decided on software. There may be some deviation but this will deviate many other parameters. For instance, there may be some deviation from initially decided static camber suppose -2degree to somewhere -2.1 or even -3degrees or 0degree?
This will further change some other characteristics like the camber again, contact patch...etc...etc...
I understand this all depends on manufacturing processes and proper care is to be taken but a slight deviation of 2-5mm can change many parameters.
economically* - without any sensors etc...
(I am myself confused...but I hope my words are clear enough to understand what I want to say... )

[Tilman]

Heyho,

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marvel:
economically* - without any sensors etc... </div></BLOCKQUOTE>

Take care of your manufacturing processes. But the only proper way to tell wether you positioned your parts/points/whatever correctly is to measure them. You can put lots of effort and money in precise manufacturing, but measuring may be easier and cheaper.

Here is a photograph of how the Delft team positioned their suspension brackets, and I believe I once saw a similar photo on the Stuttgart website.

http://dutracing.nl/wp-content...s-dut10/img_6803.jpg

[RollingCamel]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Tilman:
Heyho,

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marvel:
economically* - without any sensors etc... </div></BLOCKQUOTE>

Take care of your manufacturing processes. But the only proper way to tell wether you positioned your parts/points/whatever correctly is to measure them. You can put lots of effort and money in precise manufacturing, but measuring may be easier and cheaper.

Here is a photograph of how the Delft team positioned their suspension brackets, and I believe I once saw a similar photo on the Stuttgart website.

http://dutracing.nl/wp-content...s-dut10/img_6803.jpg </div></BLOCKQUOTE>


Ehem......kinda close to what we used..."it looks ok to me".

[Z]

Marvel,

You have discovered what 90% of real engineering is. Control of tolerances.

This includes dimensional tolerances, but also quality of materials ("so this is an aerospec bolt, eh?"), costs ("but you quoted...???"), and timelines ("two months ago you said a couple of days!!!").

All those 8+ digit numbers coming out of the computer look quite silly when you struggle to get the part positioned to the first digit.

To improve your chances I suggest:

1. A largish (say 1+ metre x 2+ metre) "build" table with a horizontal surface flat to within +/-1mm.

2. A "bubble level", preferably 2m long. Maybe two of these. They are accurate to less than 1mm over their length, and not too expensive.

3. Some reasonably accurate right-angle "squares", the bigger ones with about 0.5m sides, preferably clearly dimensioned on the outer edges.

4. Some good steel rulers and tape measures.

5. Work in millimetres, and ignore most of those digits from the computer...

Z

[Warpspeed]

This is why we always build some adjustability into the suspension.

Even if you think you know what is going to work best, some actual track testing may prove your pet theories a little bit wrong.
That is when the spanners come out, and you get to try a few different ideas.

Cumulative tolerances are the curse of practical engineering. But a few shims, some strategic threaded adjustments, and the odd alternative hole here and there can work wonders.

[Tilman]

Heyho,

there is a way to easily measure points in 3d space: With appropriate software, you can determine points in 3d space from some good photographs. I know there are companies who sell such software and objects to mount to your vehicle which will be recognised on the photos. And you need a good camera.

The theory behind all this is quite simple, however, you need to know a bit on the camera settings like focal length to determine the camera matrix (function to map a 3d point to the 2d picture).

I do not know whether there is free open source software available to do this.

[mk e]

One last point is to spend some time on the software doing a tolerance study so you actually understand how close is close enough.

It's much easier that you'd think during your optimization work to find a design that work properly at one and only 1 condition. You avoid that trap by running cases with the dimensions of each part altered. Excel has an add-on to do what's called a Monte Carlo analysis. Here you give all the components a reasonable tolerance, assume a distribution (pick normal) and then the software will build assemblies and test there performance against an equation and spit out the the performance profile distribution....so you know what could happen if you do what you're planning to do.

It's boring work and we didn't do it when I was building a car, we barely had time to actually build the car, but in industry this is the kind of work I expect to see if they expect to have engineering approval on the design or change because it's pretty important.

[bminus]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Tilman:
Heyho,

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marvel:
economically* - without any sensors etc... </div></BLOCKQUOTE>

Take care of your manufacturing processes. But the only proper way to tell wether you positioned your parts/points/whatever correctly is to measure them. You can put lots of effort and money in precise manufacturing, but measuring may be easier and cheaper.

Here is a photograph of how the Delft team positioned their suspension brackets, and I believe I once saw a similar photo on the Stuttgart website.

http://dutracing.nl/wp-content...s-dut10/img_6803.jpg </div></BLOCKQUOTE>
calling measuring easy and cheap... and showing a picture of a $50,000 Faro arm.

for the intents and purposes of this project, I agree with everything Z said.

[OspreysGoSWOOP]

I understand your pain.

You basically need to mimic the X,Y,Z coords from CAD over to real life as closely as possible.

Here is how our first year team tackled the issue. There are better methods but this is the best we could do given our tools & equipment.

I'm going to make 4 assumptions:
Your chassis is square and accurately built.
You have a flat, level building surface.
You have access to a mill.
Your a-arms are built accurately and you know your chassis mounting solution.

We created a coordinate system in CAD that we could transfer to real life.
1. CAD your build surface then mount the chassis securely at ride height.
2. CAD brackets to mount your outboard suspension points.
3. Mark the origin of your table's coordinate system. We used the first lower bar of the chassis front tube. Using a tape measure we marked the centerline then hung a plumb off the bar and marked the 0,0,0 point. This gave us a reference in both real life and CAD.
4. CAD jigs to reference your outboard points.
5. Manufacture jigs. NOTE: If you weld the jigs like we did you must machine them so the bottom and the front are a true 90deg to each other.
6. Using a mill, we zeroed off a corner of our jig and drilled the suspension holes. Your jigs are now complete and must be fastened to the table.
7. In CAD, measure from your origin to your JIG location. Use these numbers to locate your jig and fasten to the table.
8. Bolt A-arms to the jig.
9. Locate on chassis.

Here are some pictures