Hey man thanks for the interest
Before we start please bear this in mind (if I sound like I'm talking down a bit, I'm not. You probably know a hell of a lot more than I do...but anyway:
- I've worked for a kit car maker/alfa romeo service/weird car shop since 2003
- This car project was used as a final project for my industrial design degree which I started in 2003...
..and a few things about the car...
- Its designed around economical production and ergonomic features
[*]What did you use to define the chassis hardpoints?
The initial hard points where designed around the ergonomic setup of the vehicle. Vehicle seating, the ideal references of various parts from one to another -- eg the steering column to the steering rack, with minimal amount of universals for steering "feel" and also making sure that the steering will decouple in a front end accident situation.
From here came the basic vehicle proportion design: Basically what we are doing here are doing a basic development of the vehicles visual aesthetics. Good visuals always depend on good visual proportions. Check out the Golden section. There are various rules of car proportioning if you want it to look correct.
These two "requirements" (for want of a better word?) have to be juggled back and forth to get your packaging spot on.
[*]At what point did you design the suspension? Before the chassis or after?
The suspension and chassis have to be designed together. The chassis give you your arm offsets relative to your suspension track and the type/geometry you use.
[*]Do you know your roll centre and how did you decide on the suspension geometry?
The front and rear roll centers are
almost the same.
The front suspension is a classic double wishbone setup. Custom chrome molly/mild steel arms, Cortina stubaxle. Car specific geometry, include my ackerman angle, anti dive and castor.
The rear suspension is a 5 link "multilink" Independent system, which I'm still not happy with. While the front end was essentially copied from works lotus 7 replica project (as far as arms go, no pickups) then rear end was my own.
Two subaru lateral links, a track arm for toe adjustment and a adjustable amount of antisquat....well that was the idea. The problem is that it pounds the crap out of the lower coil over bush...ah well.
The upper rear upright and top links are my own...this rear end is a work-in-progress at the moment. It performs well but there are a few other problems..
[*]How did you spec your various bearings and rose joints?
The ball joints at the front are just generic Ford parts....
...however the suspension bush's are custom ones that where made at work for the clubman project. They are a poured poly bush with a mild steel inner.
The rear does have some rose joints, however I'm intent on getting rid of them. This is a road car, designed for Australian roads and it will spend quite a bit of time on dirt roads. Its just our local conditions.
Rose joints have far too much shock transmission and cause cracking on the suspension pickups in my experience. I still have 3 rose joints on my rear suspension design, I'm intent on getting rid of them.
[*]Did you do any computer modelling to package the components or design the chassis?
Solidworks.
[*]Do you know what the installed chassis stiffness is in Nm/Deg?
Local rules demand a rigidity of 3000nm/degree for a 4cyl kit car. Mine was designed around the idea of 3800nm/degree. I'm almost up to the point of doing a full scale test.
I'd say you've done an amazing job. The overall finish seems really good. The only thing I would say, is perhaps the side members could do with a bit more triangulation. I'm not sure the little cross member going from the front bulkhead to the lower tube will do a great deal as it's feeding the load from and to two unsupported tubes. You're always better to try and terminate all tubes in common 'nodes'. You'd be amazed how much material you can take out just by getting load paths spot on. It might be worth making your own wishbones at some point too since you could save quite a bit of weight if you really do the design work on them. You could probably use 1/2in tube for most of it if you get rid of the rod ends in bending on the outboard side.
The side members are opening doors, the horizontal bars are compliant side intrusion bars, that also hold up the power window mech. Doors are the second hardest thing on a car to design in my experience...
That front tube, goes from the front coil over upper mount (point of action) to the main firewall. I loose a lot of strengh if I take that out. The whole frame is designed around the idea of ergonomics and fabrication time. It's not as good as it could be, but remember this project was not intented to be a awesome dynamic supercar: The car is a GT, a tourer. I could easily double the build time to get a extra 10% of grip etc out of it and less weight, but whats the point?
Anyway I'm not sure that 90% percent of the driving public could honestly tell the difference between the two. In its place I've used ergonomics to compensate -- This is a nasty area that engineers fear to tread, car journo's will ignore because they are getting duped and car fanboys like to think doesn't exist.
Most of the wishbones I made myself. The only two are the rear lower paralell links....
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Not as good as my first post that I lost but it will do!