Charlie's no budget mid engine build: *Codename:BlakBishop*

[Nd4SpdSe]

Have you seen the "Splinter" wood car? Another project that may give you some ideas, other than the wood stuff, but it's a custom mid-engine supercar too.

[wytbishop]

I have seen the Splinter. I didn't study it, but I saw a show about it on tv last year about the team that built it. Cool concept but I couldn't help but think how heavy it would be.

Updates are due. I have been working on perfecting the rear subframe. Making sure there are no interferences etc. The design is nearly perfect in terms of fitting my vision and the functionality I want.


The suspension is based on the C6 Corvette which uses the same steering knuckles in the front and rear. The strut that secures the toe link in the rear has to be able to withstand the severe shock loading of say a pot hole.


The upper control arms are fastened to the frame with these tie bars which make it easy to adjust the alignment by loosening the bolts and adding shims.




I have now started FEA on some parts of the model.

The first simulation I ran I was like WTF??? Then I read the Inventor Guide and I realized that the simulation exaggerates the results so that you can visualize the direction of the deflection of the parts. In this view I'm applying a 1000lb force to the boss where the shock is secured to determine the stress generated in the shock mount and the deflection of the part. The blue parts are the maximum deflection in the -ve "Y" axis of 0.00658"...so that's pretty good I think.


This view shows the stress generated in the same part under the same loading. The maximum stress is in the shock mount boss and it's very small at under 3000psi.


So that's where I'm at.

[Nd4SpdSe]

I have seen the Splinter. I didn't study it, but I saw a show about it on tv last year about the team that built it. Cool concept but I couldn't help but think how heavy it would be.

Not about the materials, but maybe in terms of the mechanics and drivetrain, it's a mid-engined car too. They flipped to use the intake ports as the exhaust, and visa-versa. It's a neat idea

Target weight is 2500lbs

[wytbishop]

That is an interesting idea. Honda did an experimental Inline 4 cylinder bike back in the 90's with the intake in front and the exhaust ports coming out the back for the same reason.

I am planning on doing a custom intake manifold for the LS3 so that I can reposition the throttle body at the back of the engine instead of the front...but that's not very revolutionary. The intercoolers will be mounted in the pockets in front of the rear wheel wells and it should make it a lot easier to route the intake air to the TB. With the turbos mounted on the exhaust manifolds in the standard location it should make for a very compact intake run.

I think the hardest part of all of this is going to be building the interior surfaces and incorporating mounts for intercoolers and the intake piping and stuff. I have a concept of how it will look in my mind but I'm not sure I am skilled enough to create it in 3D.

[wytbishop]

Update....After lots of thinking and calculations I decided that the shock mount that I had originally come up with wasn't going to cut it. So after some more thinking I came up with a much stronger cast metal design more in line with the rest of the assembly. The cams and bellcranks combine to give a Motion Ratio of about .9:1 which is just fine for the wheel travel that I'll get from the Ohlins dampers.


This new design mounts the shocks longitudinally. I also designed an anti sway bar system much like the Kirkham Motorsports billet Cobra...


I also moved the rear toe link pivot a bit and eliminated all most all the bump steer from the rear suspension. According to my calculations on an 8G bump (about the equivalent of hitting a curb at 70kph) all of these parts and their mounts will hold up.


Then I went and fabbed up the front suspension pivot points...


...and located the front wheels for a wheelbase of about 107in. and overlaid a wireframe of the body.


I found a model of a Sparco seat which is at least representative of what I'll be using and an articulating model of a mannequin which I scaled up to 6'2". I need to get the general overall dimensions straight and I figured I can't just design the cockpit to fit my short a--.


Right now I'm working on sculpting the main tub. It's quite difficult and I'm progressing through the process slowly.

[Ryan]

Neat to see this is still plugging along.

I just finished a course on automotive engineering design. You can hardly cover the basics in ~50 hours. There are a staggering number of considerations and the complexity goes through the roof as you expand models to be realistic.

The ones I found most interesting were the natural human resonances, 1-2hz in pitch and ~8hz in bounce.

You've also got to consider chassis rigidity and natural frequency (or else your suspension calcs are useless)

what safety factor are you considering in your cyclic loaded parts?

[wytbishop]

Yep I'm still pluggin' away.

Sadly my education in automotive design falls well short of yours. Most of what I know I've learned in the last year and a half reading this and that on the web and a few books I've gotten my hands on.

Mostly I look at other designs to validate my ideas then I put something together that meets my basic criteria for common sense engineering. Down the road when I take this thing to the level of real mathematics, I know that there will be several elements that don't cut it and others that are way over engineered. For now I'm going mostly by feel and general common sense.

When doing suspension calculations and the few general frame strength calcs I've done so far, I'm using 4G for cyclic loading and 8G for maximum shock load. I got these values from an older chassis design book to represent a standard bump in a full speed corner and a curb at 50mph respectively. I haven't really implemented a safety factor yet. For the most part the pieces I'm drawing up are going to be stronger than they need to be...mostly because I haven't done any optimization yet. But as for fasteners and pipe and plate thickness and so on, if it's strong enough to withstand an 8G shock load I imagine it will hold up to daily driving.

The main tub is done and at the moment I'm working on the roof. I've also been putting together a few things just to flesh out the front end. A fuel cell, a rad and I'm pretty proud of the front dam. I will have to do some flow calculations on that later, but for now I'm matching things to the images in my mind.