Fred W B
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| posted on 29/10/07 at 08:15 AM |
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Starting out advice - midengined scratch build
A friend of mine who is not big on literature research is talking about starting a scratch build mid-engined full body sports/race car project, and in
conversation with him I am reminded of things I have learnt during the process of my build so far.
I note below some of my thoughts on how to approach a project like this. I understand that the below is spelt out in much greater detail in various
excellent books and websites and is being discussed on other threads, I post it here as a summarized version. If I had followed these recommendations
when I started, I would have saved myself considerable time, hassle and expense.
When starting out at least do the following, in this order:
Decide what the car is going to look like, i.e what body shell, if not original. This also determines wheel base dimension and the width over wheels.
i.e determine the wheel positions.
If original body, decide on at least the front and rear track, wheel base can be adjusted.
Decide on what tyres you will use, exact width and profile, and procure if you are serious.
Decide on what hubs/uprights/steering rack you will use and procure/make if you are serious
Decide on what rims/offset you will use and procure if you are serious
Decide on what engine and transmission you will use and procure if you are serious.
Position all above parts on garage floor or build table and sort ergonomics – where do you fit?
If you are going to draw up in cad, finalize the position of all above parts in your model only now.
All the above could be an iterative process, but please complete it BEFORE you start the chassis.
Design suspension – if you are not going to do the research to enable you to do this yourself the only options are:
Get someone else to do it for you
Copy an existing car, strictly only valid if using that cars uprights/hubs/wheels/tyres.
Guess
Once you know where the inner suspension points are, you can design the chassis, to accommodate all above. CAD / balsa model / cut and tack on build
table are all valid methods, but best results would be obtained by combining them. Please do not start with a Locost chassis and try to modify it to
accommodate a RWD drive train.
Cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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RazMan
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| posted on 29/10/07 at 10:01 AM |
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Fred, just to expand on the ergonomics point - try and find a similar cockpit and take measurements of the relationships of seats, pedals, column and
gearshift. Then draw your 'personal space' including head & elbow room and make sure you put this into the mix as soon as you can.
[Edited on 29-10-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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nick205
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| posted on 29/10/07 at 10:21 AM |
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One other point I would make is to try and build in some adjustability wherever possible. e.g. pedals, steering column, seat position etc. IMHO
being able to get a good driving position takes precedance over most other aspects of the car. If you can't get comfy and feel at ease with the
car you'll never enjoy driving it.
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Ringius
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| posted on 29/10/07 at 04:16 PM |
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The really nerdy approach to ergonomics
Since I am a real nerd...
1. I have started by purchasing a seat.
2. Around the seat, I am currently building a mock including pedals, steering wheel and gear lever.
3. Using a gaming wheel, pedals and shift lever, I will use the mockup and spend some hours in front of my favorite racing sim (which means testing
the ergonomics for hours on end)
4. Based on input from the gaming sessions, adjust ergonomics and re-iterate.
I would have thought that it would be better to sort the ergonomics first, and then decide on wheelbase; I find it difficult to find space for the
pedal assembly when taking the front wheels turning angles into consideration - is this a problem i real life?
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sgraber
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| posted on 29/10/07 at 04:45 PM |
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For my .002 cents the ergonomics are huge as was already pointed out. Getting the steering wheel and shifter to fall into hand are important as is the
brake pedal position relative to the accelerator.
I think that your steps are in order but I want to elaborate on the process. I think that one of the more important things to do asap is ensure that
you get the wheel scrub radius not going positive outboard of the wheel centerline. It is so important to get that right as this is how you get good
feedback through the steering wheel from the tires and self-centering. I know this because I had to re-design my upright KPI location after I chose a
taller tire and threw my scrub radius outboard of the wheel centerline. Once I brought it back 4mm inboard of the centerline, my self-centering came
right back and the steering feel was much better.
So at the very outset you must pick an upright design for the front of your car, determine your total rolling radius of the tread, then figure out
your scrub radius based from the KPI. That then lets you pick the correct backspacing on the rim. From that point on you don't change the tire
diameter unless you re-calculate your scrub radius.
Hope I am not going into too much detail. Since you were just posting a summary, but I think that the scrub radius issue is overlooked a lot and IMHO
is really important to a great handling sportscar.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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Fred W B
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| posted on 29/10/07 at 06:44 PM |
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Good points, thanks. Input is welcome, just want to build a thread that can be refered to.
Ringus -
quote:
I would have thought that it would be better to sort the ergonomics first, and then decide on wheelbase; I find it difficult to find space for the
pedal assembly when taking the front wheels turning angles into consideration - is this a problem i real life?
Exactly, thats why I said
quote:
If original body, decide on at least the front and rear track, wheel base can be adjusted.
If you are using an existing body your wheel base is fixed for you.
Depending on wheel base and engine layout, packaging all the bits under and around the drivers feet can be a major challenge. The exercize you are
doing is a very valid one.
Cheers
Fred W B
[Edited on 29/10/07 by Fred W B]
[Edited on 29/10/07 by Fred W B]
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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Ringius
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| posted on 29/10/07 at 07:34 PM |
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Fred!
Thanks for your input, and sorry for not reading thoroughly enough.
Now waiting for Kiminis "read my book" (which I, btw have done already  )
BR,
Ringius
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kb58
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| posted on 29/10/07 at 07:50 PM |
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Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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andygtt
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| posted on 1/11/07 at 04:32 PM |
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quote:
Originally posted by Ringius
Since I am a real nerd...
1. I have started by purchasing a seat.
2. Around the seat, I am currently building a mock including pedals, steering wheel and gear lever.
3. Using a gaming wheel, pedals and shift lever, I will use the mockup and spend some hours in front of my favorite racing sim (which means testing
the ergonomics for hours on end)
4. Based on input from the gaming sessions, adjust ergonomics and re-iterate.
nerd
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andygtt
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| posted on 1/11/07 at 04:32 PM |
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[
[Edited on 1/11/07 by andygtt]
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Ringius
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| posted on 2/11/07 at 12:12 AM |
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I'm a nerd - and I'm proud
[Edited on 2/11/07 by Ringius]
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mr henderson
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| posted on 2/11/07 at 04:01 PM |
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I would suggest getting other people to sit in it as well, maybe one really tall person and a short person just to check that if the resulting car HAD
to be driven by someone else (for instance, if you sold it in order to finance the Mk 2 version), then that would be both comfortable and safe for
them
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Ringius
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| posted on 2/11/07 at 11:55 PM |
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Really good point. By the time I am done, my sons will probably have their licenses, I they are both seem to become taller than I am.
(currently I THINK I would let them...)
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andygtt
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| posted on 3/11/07 at 07:52 PM |
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quote:
Originally posted by Ringius
I'm a nerd - and I'm proud
[Edited on 2/11/07 by Ringius]
lol, glad you took my comment in good spirit as I have just realised you are not the person I thought I was ribbing (similar advatar).
Not my usual greeting.
Andy
please redefine your limits.
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Delinquent
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| posted on 3/11/07 at 11:20 PM |
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quote:
Originally posted by andygtt
quote:
Originally posted by Ringius
I'm a nerd - and I'm proud
[Edited on 2/11/07 by Ringius]
lol, glad you took my comment in good spirit as I have just realised you are not the person I thought I was ribbing (similar advatar).
Not my usual greeting.
For some reason I'm tempted to ask who you did mean then Andy
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andygtt
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| posted on 4/11/07 at 07:59 PM |
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rumbled
Andy
please redefine your limits.
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Delinquent
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| posted on 4/11/07 at 08:03 PM |
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Do you honestly think I'd be nerdy enough to set the seat up with my playstation steering wheel and pedals? Course not.
I used a plastic school chair, a dinner plate and a file box
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Ringius
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| posted on 4/11/07 at 08:09 PM |
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Would be fun though ,wouldn't it
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