Tralfaz
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| posted on 12/5/07 at 05:09 PM |
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Ackermann,well actually,the "lack" thereof...
Damnit.
I thought I had everything sorted. I am scatch - building a Lotus/Cater-something replica (Series III sized chassis) and had finally sorted the
Suspension (First in Susprog,now in real life).
Everything was going so well, nice Camber Curve, inboard dampers with 1:1 motion ratio. Anti-Roll bars designed.
As you Brits say: Happy Bunny.
Yet...
Somehow I overlooked the Ackermann.... Best I can manage so far is only slightly better than parallel motion. Due to the inboard dampers it is
impossible to move the rack any further back. The only option I see is if the car behaves poorly, is to have the Upright steering arms heated,bent
and heat-treated back to strength, or I suppose fab some up.
Anyone running with nominal Ackermann?
Thanks,
T (Presently training to push an unruly car around the paddock)
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Ivan
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| posted on 12/5/07 at 08:35 PM |
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I wouldn't worry too much about ackerman at this stage. The literature is quiet confusing to me about the benefits or otherwise of ackerman -
some say excessive ackerman improves turn-in - others say it makes little discernable difference. Milliken in Race Car Vehicle Dynamics makes mention
of many race cars with negative ackerman so I think unless you have excessive inner wheel scrub at high steering lock at parking speeds don't
bother.
I would certainly wait to drive the car and if it feels wrong get an expert driver to test it and comment on whether ackerman will correct the
problem.
I am not convinced that the majority of us are good enough drivers or experienced enough race engineers to understand our vehicles dynamics or to know
definitavely what settings will make what difference when it comes to things like ackerman. I know for sure I'm not.
ps - if your avatar is an indication of your research resources you wont find the answer looking there 
[Edited on 12/5/07 by Ivan]
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Tralfaz
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| posted on 13/5/07 at 12:07 AM |
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I had the same "slightly confused" feeling after reading all the somewhat conflicting opinions on Ackermann. Though it does seem in some
of the more recent writings that Ackermann is desirable.
I agree it is not worth fussing with now,though I would still be curious to here any feedback from other Seven builders.
T
PS - No answers to my suspension questions "down there",but it does reassure me that one can still work with substandard equipment...
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britishtrident
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| posted on 13/5/07 at 07:46 AM |
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You need some ackerman -- how much is a good question. Negative ackerman has the potential to give slightly more grip in high speed comsant radius
curves but it can also give very nasty handling characteristics.
Provided the steering arms are forged steel bending the steering arms is ok provided you can get enough localised heat ---- ie using a oxy-propane or
oxy-acetelene cutting torch. Concentrating the heat on the compression side of the bend.
Don't try to do it unless you can get enough localised heat built up quickly --- straw yellow.
As for heat treatment --- I am only guessing but use compressed air jet for the quench then gentle reheat to a lower temperature and allow to cool
slowly.
However I wouldn't ever try bending the heating steering arms that were high strength nodular cast iron (Ford use a lot of this).
The easy way to test for cast iron is that when ground with an angle grinder it produces horrible black carbon dust, steel produces grey dust.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Uphill Racer
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| posted on 13/5/07 at 07:47 PM |
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Ackermann doe's virtually nothing in high speed corners (not enough steering input). It is in tighter corners that it, or lack of it is noticed.
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britishtrident
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| posted on 14/5/07 at 02:18 PM |
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quote:
Originally posted by Uphill Racer
Ackermann doe's virtually nothing in high speed corners (not enough steering input). It is in tighter corners that it, or lack of it is noticed.
For high speed turns in some types of racing (particularly in the USA) negative ackerman is used, The theory is that the lmore ightly loaded inside
wheel will contribute maximum lateral grip at a lower slip angle than the outside wheel.
The theory is good, in practice I think the disadvantages far outweigh any small advantage.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Uphill Racer
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| posted on 14/5/07 at 08:25 PM |
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Agree that if the sport only has high speed bends Akermann may not be important but in the real world of slow to medium speed bends (tighter) as well,
100% Akermann is best IMHO.
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MustangSix
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| posted on 16/5/07 at 05:08 PM |
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Having driven a couple of traditional hot rods with zero and negative Ackerman, I can tell you, you want it on a street car. Parking lots and 90
degree (especially right hand) turns are much more difficult without it. Negative Ackerman may be good on a dirt track race car, but not on a
driver.
I've bent the forged arms on Ford spindles to accommodate dropped axles on several cars. It's a time-honored traditional modification.
Just heat the area to be bent to cherry red, then bend with a large set of pliers or a wrench. Do not quench with water or air. Just let it air
cool. I've seen some guys bury the piece in dry sand or kitty litter so that it cools slower, but I'm not sure it really makes that much
difference.
[Edited on 16/5/07 by MustangSix]
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Ivan
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| posted on 20/5/07 at 04:59 PM |
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Found this thread with possibly the best article re Ackerman I have read.
http://www.clubracer.com.au/articles/ackerman.asp
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JoelP
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| posted on 20/5/07 at 08:58 PM |
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id love to read that article but the font is ridiculously small - how the hell does anyone read that?
Any way to enlarge it? I get as far as view source and get lost in the html.
[Edited on 20/5/07 by JoelP]
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Peteff
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| posted on 20/5/07 at 10:51 PM |
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Use firefox
and press control and + 
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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Uphill Racer
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| posted on 20/5/07 at 11:20 PM |
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Basic, you need toe in with Akermann to give anti at small turn angles. It did'nt say anything new.
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MikeRJ
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| posted on 21/5/07 at 07:36 AM |
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quote:
Originally posted by JoelP
id love to read that article but the font is ridiculously small - how the hell does anyone read that?
Any way to enlarge it? I get as far as view source and get lost in the html.
[Edited on 20/5/07 by JoelP]
That page is horrible in IE, you can't resize the text and it is far too small. With Firefox you can resize the text as normal by pressing Ctrl
and using the scroll wheel.
If you don't have it yet then definitely stick Firefox on your PC. You don't have to use it all the time and it coexists quite happily
with IE (IME!), but it is very useful in situations like this.
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britishtrident
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| posted on 21/5/07 at 07:16 PM |
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IE will resize text also istr its on the View drop down menu
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 21/5/07 at 07:19 PM |
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Thing to beware is too much ackerman -- most 60s and 70s cars had way too much remember the Rockford Files car chases, tyre on inside front wheel
squealing as it got dragged sideways in tight turns
[Edited on 21/5/07 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Tralfaz
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| posted on 21/5/07 at 07:51 PM |
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Well... I went ahead and modified the steering arms, rather then bending I reworked them by cutting and welding.....
Before you all freak out, I didn't cut and weld the arm itself,but rather the end... I welded shut the exisiting tie rod hole, cut out a
semicircle further "outward" welded in a piece of thick walled tube (3/4"OD 1/2"ID) Then spent hours welding
grinding,welding,grinding to get a nice solid bit. I took care to not build too much heat. I plan on doing a stress test, but I think it will be just
fine.
Thanks to all
Brian
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worX
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| posted on 21/5/07 at 09:23 PM |
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because I am a complete PC numpty I don't know about (and don't want to know about in case I burst!!) firefox and stuff like that - what I
don't understand is why you don't just copy and paste the page into word and then make the text bigger and also black???
quote:
Originally posted by JoelP
id love to read that article but the font is ridiculously small - how the hell does anyone read that?
Any way to enlarge it? I get as far as view source and get lost in the html.
[Edited on 20/5/07 by JoelP]
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JoelP
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| posted on 21/5/07 at 09:34 PM |
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i did, about 5 mins after i posted  However, then you have to crossreferrence to the site for pictures, but maybe thats because i used notepad not
word.
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worX
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| posted on 21/5/07 at 11:20 PM |
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well why didn't you put it into word, that way the photos would of gone aswell wouldn't they? they did with mine, but I don't know
if my Word prog is diff to yours?
quote:
Originally posted by JoelP
i did, about 5 mins after i posted However, then you have to crossreferrence to the site for pictures, but maybe thats because i used notepad not
word.
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MikeRJ
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| posted on 21/5/07 at 11:45 PM |
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quote:
Originally posted by britishtrident
IE will resize text also istr its on the View drop down menu
Normaly IE will resize text...but mine won't on that page, whatever I select I get same size font.
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