Mark Allanson
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| posted on 14/2/03 at 10:11 PM |
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Even more accurate front suspension
The "accurate front suspension" thread has got a slow cos we have all added about 85937826 zillion megs of images to illustrate our suspension
problems.
The upshot is that my brackets are in the "wrong" position, but they are perfectly parallel and symetrical, AND the sit well on the lala tubes (sounds
like bleeding teletubbies). I don't really want to move them because they look right, and having them half on and half of the upright tubes just does
not look right to me.
This leaves be 22mm to find to get the right castor angle (a Cortina only has 1.5 degrees of castor, why do we need 5.5?). I have used my really
expensive CAD Program (wooden ruler and a biro, and a son who can use adobe sweatshop) to draw this diagram of an even more asymetrical upper wishbone
to give the assumed correct castor angle.
Can anyone see a problem with this, or got a more elegant solution to the problems of RC's crap maths?
Answers on a postcard.......................
 
Rescued attachment AltWishboneSML.jpg
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chazpowerslide
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| posted on 15/2/03 at 11:40 PM |
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Mark, the main thing is that your brackets are symmetrical and parallel to the centre line of the chassis.
Castor is contributes (as does KPI) to the "self center" feeling to the steering and the "feel" of the steering in a turn (the resistance you feel
acting on your hands in the opposite way to that which you are turning)
Too little castor and you may not have much of a clue as to what the front wheels are doing as the steering will appear "light" and won't weight up
when cornering, the car may also wander or feel un-stable or un-settled when running straight.
Too much castor and the opposite happens.
Anything between 1.5 deg and 6 degrees seems to be ok.
The drawing you posted is probhably right for YOUR chassis if you measured it correctly as they all seem to vary considerably.
Don't take 5.5 degrees as gospal a lot of it is up to personal feel.
As long as you know what you've built into your chassis so you have a starting point for adjustments you should be ok.
I was involved in the builds (ie did most of the work) of two book Locosts very early on (within 6 months of the orogional book)
The first was done "by the book" and the second we modified due to the problems we had with the first (front suspension)
The first Chassis had a castor of 2 degrees and to get the second "right" we modded the top wishbone as you propose.
Both cars handled accaptably the second had better steering charaistics but had better (avo) shocks poly bushes and a quick rack so they were not
realy like for like comparisons.
AFIK both of my Westfield chassis have 5 degrees of castor but I'd have to check to be certain.
HTH
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Stu16v
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| posted on 16/2/03 at 01:05 AM |
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quote:
(a Cortina only has 1.5 degrees of castor, why do we need 5.5?).
The weight thing. The more weight bearing down on the front axle, the more the 'self steering' effect is created. The weight acting on a Cortina
Mk3/4/5 is probably as much as the total weight of a completed Locost. Hence the reason the Locost needs more castor.
HTH Stu.
Dont just build it.....make it!
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davef
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| posted on 17/2/03 at 06:18 AM |
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Hi Mark that drg of the wishbone would set your castor right, but it would foul your coil springs, go for then MK style, ie a full u shape then cut
and position your threaded boss where you want it. cheers davef.
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Mark Allanson
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| posted on 17/2/03 at 07:45 AM |
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I've got a small hand powered bender, it looks like the best solution - thanks
Mark
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philgregson
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| posted on 18/2/03 at 09:56 AM |
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Just a couple of questions then:
If book two is wromg re. the front suspension geometry is it the same as book one - i.e. is that wrong too?
What about all the people who have completed builds 'by the book' - Have you noticed any problems with the steering geometry?
Phil.
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davef
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| posted on 19/2/03 at 06:32 AM |
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Hi Phil, i don,t think most people will have thier suspension set wrong, it will eventually dawn on them something is not quiet right. when they see
the top front bracket does,nt appear to sit right on the front uprights, but you can get round the problem by welding in a gusset like mentioned
earlyer.in fact if you look at the picture on page 105 in the 2nd book you can see the top bracket does,nt look to be sited correctly, but it will be.
thats why i said to any person just starting out on a new build,they should make the wishbones to book, but make the front chassis member page 49 fig
4.10 to a new measurement of 100mm instead of 76mm , plus shorten top rails j1 and j2 by 25mm and the problem disappeares. cheers davef.
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Hornet
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| posted on 23/2/03 at 08:45 PM |
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had to change from book
I have decided that adding gussets is not what I want.. so I have uploaded photos in my section so that new builders do not make the same mistake..
not that it was my mistake 
The front braket is too far off LA and LB for my liking.
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Mark Allanson
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| posted on 23/2/03 at 10:43 PM |
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Pretty drastic stuff, but I know where you are coming from, I have gone the other route, I have redesigned the top wishbone to compensate. Let me know
how you get on
Mark
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Rorty
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| posted on 24/2/03 at 02:27 AM |
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Hornet, even though the top wishbone doesn't see the same loads as the bottom one does, the way those top wishbone brackets are attached looks
downright dangerous. The "ears" of the brackets need to be properly supported.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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Hornet
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| posted on 24/2/03 at 10:01 AM |
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Soz Rorty, think i have confused you.. this is a long running debate, My pictures show my top brackets as per the book dimensions. I have now took
the bull by the horns and removed the front end and will start again with LA and LB 25mm further back to give a better position for the top
brackets.
Cheers.
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davef
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| posted on 24/2/03 at 11:22 AM |
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Hi Hornet just checked your chassis surgery, it,s not that painful is it. cheers davef.
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Rorty
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| posted on 25/2/03 at 01:45 AM |
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Hornet:
quote:
I have now took the bull by the horns and removed the front end and will start again with LA and LB 25mm further back to give a better position for
the top brackets.
PHEW!
Any pics of the mods yet? 
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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jcduroc
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| posted on 26/2/03 at 11:49 PM |
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Accurate [front] suspension(s)
Rorty
Pls read my post on "Accurate front suspension"
Joćo
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Hornet
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| posted on 4/3/03 at 07:09 AM |
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Here is a pic of the brackets in postion with LA and LB 25mm further back.
Much better area of contact.... you have been warned.
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