sgraber
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| posted on 9/2/04 at 03:25 AM |
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Weekend progress
Made some prgress on the car this weekend. Rollbar is almost finished, just need to add bracing. Engine undertray is almost finished too.
I took a neat photo of the car out of the 2nd story window. I turned the wheel full lock to see if there is Ackerman or anti-ackerman. You be the
judge.
Latest progress on La Bala
Later,
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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Spyderman
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| posted on 9/2/04 at 02:02 PM |
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Steve,
Looking good! (the car that is) 
It looks like you have some positive ackerman as the inside wheel is turning slightly more than outside. How much would be difficult to see without a
proper plan view. Does it look the same when turned the other way? 
Did you raise the windshield frame any or leave it?
I still think those seats look very upright. Can you recline them any?
Terry
Spyderman
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ProjectLMP
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| posted on 9/2/04 at 03:08 PM |
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Looks good. When are you going to start the bodywork
Looking at your steering arms I can't see how you would have anything put positive ackerman. How much I can't say but definitely not
negative.
[Edited on 9/2/04 by ProjectLMP]
Home of the Astronomicalcost Mid engined LMP project
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andkilde
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| posted on 9/2/04 at 03:29 PM |
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On the subject of Ackerman...
(sorry for the silly questions, still waiting for my books to arrive)
Are there methods of theoretically calculating what ackerman will be based on a given suspension configuration?
I know that the inner and outer tires travel through different arcs in a given turn -- can you simply calculate what ackerman should be with a compass
and protractor (ie. draw two circles, one at inner tire radius, one at outer and determining steering angle for each wheel? Perhaps at several
different turn radii, then express it as a percentage.
Or do you have to take other factors into account?
Am I right in assuming that not enough ackerman will lead to understeer (inner tire will push car off-line)?
Thanks, Ted
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kb58
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| posted on 9/2/04 at 03:50 PM |
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Ackerman is a hotly discussed topic, there isn't yet a perfect formula about what works. Worse (or better) since everyone is different, you may
prefer it different then the next guy.
Ackerman is tough to discribe in words, a drawing is much better. The drawing I've seen essentially shows lines projecting from the steering
arm on the front uprights. These lines project rearward and cross, for "perfect" Ackerman, at the center of the rear axle.
"Perfect" in this case means if you turned the car on a gravel road, it would not disrupt the gravel. This, believe it or not, was the
original reason for Ackerman... I think it came from the horse-drawn carriage days.
A practical aside why you might want to leave it as you have (with positive Ackerman) is this: When your car is done and you take it to track events,
it is very likely you'll need to push it through the pits. With "perfect" Ackerman you will have no problem doing so. But if you
have either no Ackerman, or negative, the car will be very difficult to push!
Carroll Smith, in his early books, said Ackerman was a bad idea, and had reasons why. Then in his last book, "Engineer to Win," he
changed his mind. During testing they had some spare time one day and set out to see the effects of changing Ackerman. They'd make a change
and the driver would take it out for a couple laps. The end result, which Smith admitted didn't fit his theories, was that the *more* Ackerman
the car had, the easier the car turned in, so it was easier to drive. Easy to drive = faster car.
In the Staniforth book he felt that anything that made the car hard to push was surely a bad thing, and as I recall, recommended positive Ackerman.
For my Mini I was going to have no Ackerman, per suggestions from the Milliken book. But after reading Smiths comments I dialed in as much as
possible. In the case of my short-wheelbase Mini, it means almost, but not, quite, having perfect Ackerman. (I couldn't move the arms outboard
enough to "point" them at the rear axle centerline.
And to potentially counter everything said above, keep in mind the Ackerman issue is only debated for a track car, not a street car. Most racecar
designers would say perfect Ackerman is the best for a street car. So... it may depend on your application, though if you believe Smith's
findings, then "perfect" should be fine...
[Edited on 9/2/04 by kb58]
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pbura
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| posted on 9/2/04 at 04:22 PM |
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It looks like you have Ackerman from the overhead photo, i.e., inside wheel turned a bit more. As Kurt says, if the car is easy to push around, then
you have it 
Y'know, your car looks low but is no peanut compared to your family sled, even though it's light enough. Very good! My thinking on size
is that if your components are large, and I'm thinking principally of the rear axle, why not use the space for bodywork if you can keep the
weight down? There's nothing lost in handling, the car will be more comfortable, and you'll be less likely to get run over!
Nice job on the roll bar, too. Are you sure you won't clunk your head on it in neck-snapping acceleration? As far as actual roll protection,
it should keep you from being squished, especially with the windshield frame to help out. Knock on wood, of course!
Pete
Pete
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sgraber
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| posted on 9/2/04 at 04:50 PM |
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Nice words on the Ackerman effect Kurt. Well put. I did measure the Ackerman effect and it is positive, but not perfect. The intersecting line is
about 8" behind the axle.
Pete, the car is not too small. Not like a 7. It's an 'American' proportioned car eh? I'd like to make my next car smaller
and lighter. Reading Paul Stockleys latest updates on his website brings that into closer focus for me. Thanks Paul! I think I can easily lose 150Lbs,
maybe 200, without too much effort.
I think this building effort is really all about prototyping and learning how to build and what to build, so I can make the next one better.
Terry, I am going to tilt the seat back. I should gain another 2-3cm. I'll have to see if the "steering wheel-shifter-pedals"
positioning is acceptable.
BODYWORK!>? HA!   .... soon.....
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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ProjectLMP
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| posted on 10/2/04 at 01:44 AM |
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One thing to say about ackerman is that there is no such thing as "Perfect Ackerman". The optimum amount depends on a number of variable
factors such as speed, radius of corner, tire construction and the list goes on. Really perfect ackerman would probably need to be active and
constantly changing depending on lots of parameters.
The following I think is spot on:
"I think this building effort is really all about prototyping and learning how to build and what to build, so I can make the next one better.
"
I think when dealing with complex projects its far easier to evolve your way to perfection than get it perfect the first time. Just about all road and
race cars are evolutions based on designers past projects and experiences.
The only bit I want to get right first time is the bodywork (the thought of doing it multiple times fills me with dread). The first chassis is only a
stepping stone so I can build a better one later on.
Home of the Astronomicalcost Mid engined LMP project
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Alan B
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| posted on 10/2/04 at 02:31 PM |
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quote:
Originally posted by ProjectLMP......I think when dealing with complex projects its far easier to evolve your way to perfection than get
it perfect the first time. Just about all road and race cars are evolutions based on designers past projects and experiences.
The only bit I want to get right first time is the bodywork (the thought of doing it multiple times fills me with dread). The first chassis is only a
stepping stone so I can build a better one later on.
So true.
I'd say I could have done about 5 new iterations of my chassis for 1 new body iteration...
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sgraber
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| posted on 10/2/04 at 03:11 PM |
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I tried to get this in before Alan posted, but the damn sites been so squirley... HOWEVER>>> It seems to be working GREAT now! 
The thought of doing bodywork "once" fills me with dread too. Just seeing Alans neverending quest has filled me pants with dread several
times over! Ohhh shite! (can I say that on TV?)
Later,
Graber
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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pbura
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| posted on 10/2/04 at 04:14 PM |
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On the very positive side, you can use what Alan has learned about shaping and finishing bucks; he's making it look easy these days.
I was looking at your website and your original 3D renderings. Have you updated your drawings for the new design? If not, that might be a good place
to start.
Pete
Pete
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Alan B
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| posted on 10/2/04 at 05:43 PM |
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quote:
Originally posted by pbura
On the very positive side, you can use what Alan has learned about shaping and finishing bucks; he's making it look easy these days.
.......
Pete, very true. In many ways it is fairly easy now, I've learned a lot...where to focus time and effort, where not to...which materials shape
up easiest...what surface works well...A ton of stuff really
There are things I would do differently, but a lot has been learned.
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