The rear suspension is getting somewhere

Last time the rear suspension was giving me headaches, it was very frustrating. Well, it turned out that some of that was due to constraints initially set between one of the control arms and the upright. What I did now was to make a skeleton for the suspension, i.e. I inserted a part into the product which defines the pivot points on the chassis. This way I managed to get a rough estimation of where the pivots should be. Which means it's now back to measuring the drawings and figuring out where the suspension should attach to the frame... I also need to examine the suspension and decide what kind of joint should be used where, it doesn't seem appropriate to use only ball-joints but maybe I'm missing something.

Pictures speak a thousand words, so here's what I have for you today:

Rear suspension in progress

Yet another critical item to get right in a racecar is the suspension. So I had better model it, hadn't I? I have concentrated on the rear first simply because I found it more interesting

It seems I will need to look for bigger wheels...

The rear knuckle

I can't remember if I ever put pictures up of the rear knuckle I modelled before getting the deal to model the IMSA spaceframe for Paul. In case I didn't post them, here they are

IMSA update

Not a lot has happened since my last post, but it hasn't been standing still either. As I wrote earlier, the chassis stiffness was up at 8139 Nm/deg in my FE analysis. Not too bad, but really not excellent either.

So, what improvements have I found? Well, there were limits to what could be done. Paul figured that adding tubes in the floor on the driver side would get in the way of his seat and pedals. I agree that it might result in a higher CGH. It's all a compromise and in the end, it is Pauls car and his word is law.

But I did add a brace to the floor on the passenger side. If Paul was to have a passenger with him, the extra weight of the passenger would be more of a problem than the slightly higer CGH anyway.
With the floor brace, the stiffness was now 9811 Nm/deg.

I then looked at further triangulation of the passenger compartment but didn't get higher than 10313 Nm/deg and I considered this to be a pretty small gain. It just didn't seem to be worth it.

Having studied the deformed mesh, I concentrated on the rear end. I added some braces connecting the engine mounts and the square section tubing at the rear. This time, the results were a bit more interesting: 12649 Nm/deg.

Now, while this was a nice improvement, I am aware that these braces could come in conflict with the driveshafts. Unfortunately, Pauls attention has turned towards a different project at the moment, so he hasn't been able to check this yet. Until he has checked this, or come up with another idea on chassis improvements, I guess there's not much more I can do right now.

Here are a couple of pictures of the frame in its current form

Enjoy

PK

Spaceframe comparison

 

Finally it seems I have the spaceframes modelled up. Above is a picture of the original IMSA frame

And here is a picture of Pauls spaceframe. I know the frames aren't exact, as an example they lack suspension pickup points. But they're both close enough for now. Further refinement will be made.

 The point was to compare the torsional rigidity of the frames and then work to find improvements for Paul. The picture above shows how I set the analysis up. A virtual part was attached to the front rectangular beam which will house the attachment points for the front shock absorber. This part was then rotated 1 degree around the longitudinal axis. At the rear rectangular beam, another virtual part was applied and this was clamped.
I do know this is not really the correct way to do it if you want values to compare to the real world, but for comparing spaceframes and see if improvements can be made I felt it would be good enough, especially since there's a limit to what I can actually do on my computer.

For Pauls spaceframe, we suspected that the engine would act as a cross brace. I decided to model this by adding an infinitely stiff virtual part connecting the engine mounts.

For the analysis, a full-on 3D analysis seemed appropriate. To speed up the computations, the mesh size was set to 20mm with a sag of 10mm using parabolic elements. Material was set to steel.
And the results?
For the IMSA spaceframe pictured at the beginning of the post, a moment of 6168Nm was recorded.
For Pauls spaceframe, not including the effect of the engine/transmission, the moment was 6824Nm.
When the transmission was taken into account, the moment increased to 8139Nm.

I am confident that we can find ways of increasing torsional rigidity for Pauls car. As a reference, speedlab have their corvette racecar up at 18000Nm/deg

Now, next on the to do list is finding improvements

Hosler's IMSA

What you see in the pictures above is a wet dream of many Fiero enthusiasts. This is an IMSA Fiero, a real one, not another bodykit on yet another "ordinary" Fiero. This particular car is owned and driven by Paul Hosler. Before we continue, have a look at the rest of the pictures. If you know anything about the IMSA Fiero, you will notice immediately that Paul's car isn't original. He modified it to take a V8 with a Porsche transaxle. Yep, that means that the drivetrain now sits longitudinally in the car. Notice also how clean his car is. And his garage. My garage has never been this tidy.

I first got in touch with Paul as I was trying to find information on the IMSA chassis. I figured it would make an interesting CAD project and Paul sent me a scan of the drawing for the rear upright just to let me have a taste of what I was getting myself into. Being me, I couldn't resist to model the upright and send Paul an IGES. Apparently, this was appreciated as Paul made me an offer I just couldn't resist: he would send me drawing scans and measurements and I would model the original chassis and his modified version. The plan is to compare the torsional stiffness (between the original and Pauls version) and see if any improvements can be had.
Now, this is where I would post pictures of the CAD model, but I'll save those for the next post.