ned
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| posted on 9/2/04 at 12:54 PM |
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trailing arm position
Any ideas if this would work, with the exception of the problem that the driveshaft might hit the top trailing arm under bump.
Image deleted by owner
Ned.
beware, I've got yellow skin
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philgregson
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| posted on 9/2/04 at 01:38 PM |
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Ned
Some one will probably correct me on this but I think that the efective length will be where the axle is regardless of the trailing arm length
although the geometry will vary slightly beacuse the axle will move vertically relative to the arms.
probably doesn't make a lot of sense but if you draw it it becomes clearer - but not if you draw it wrong - bugger!!
Cheers
Phil
[Edited on 9/2/04 by philgregson]
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philgregson
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| posted on 9/2/04 at 01:42 PM |
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bugger!
I'm not so sure now.
I was thinking that the forces would act as if applied to the arms where the axle was but that isn't the case - the force will be applied at the
pivots on the end.
It's all clearer now - I was wrong - sorry.
So - yes it should work. you could increase the vertical spacing of your trailing arms to reduce the chance of it fouling.
Inceasing the spacing further at the car end would help and could also be used to dial in a certain amount of anti-squat or anti-dive, depending on
which way you moved them.
Phil
[Edited on 9/2/04 by philgregson]
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Jon Ison
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| posted on 9/2/04 at 01:55 PM |
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may help, may not,
but to get things clear in my head when i was racing off road and building chassis i used to make "card board" mock up ups, out of flat
card use drawing pins for pivots and see just what happened when i moved things around.......
just a way of getting a clearer understanding in me fick head...........
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ned
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| posted on 9/2/04 at 02:02 PM |
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Thanks for that Jon!
Having read suspension books it appears the minimium legnth of trailing arm should be 8" and I've changed my chassis as I was originally
going to make it IRS.
as a consequence I've removed the book chassis trailing arm mounts and changed the bulkhead tubes, so need to mount the trailing arms points to
these as I'd rather not hack it all apart again.
with it correctly setup I don't see why it should cause a problem. I just wondered if there was a specific reason that with dedion or live axle
cars the trailing arm mounts have always (from pics i've seen) been directly (vertcially) above and below the axle.
Cheers,
ned.
[Edited on 9/2/04 by ned]
beware, I've got yellow skin
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GO
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| posted on 9/2/04 at 02:23 PM |
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Ned, all you've done is make it kinda like an unequal length wishbone, so should be fine. I think. 
Worth doing as the Isonmaster says though and make a scale cardboard mock up.
[Edited on 9/2/2004 by GO]
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James
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| posted on 9/2/04 at 02:46 PM |
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Ned,
If you replace the 2"x1" with 1"x1" then you won't need to worry about this!
Assuming the Locost design is ok then it's one less potential bollok to be dropped!
If you're really desperate to keep your 2"x1" then move it inboard by an inch (if you can fit it!)
Just an idea to keep things simpler! But I know you won't listen to me!
James
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ned
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| posted on 9/2/04 at 02:51 PM |
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quote:
Originally posted by James
I know you won't listen to me!
Damn right I won't 
Ned.
beware, I've got yellow skin
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Surrey Dave
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| posted on 9/2/04 at 05:18 PM |
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I dont know much about this kind of thing but it looks as if the more offset you have between the axle hub centreline and the rear trailing arm
mounting, the more twisting force your putting into the whole set up ,even at stand still.
If for instance the axle was 1 metre forward of the trailing arm rear mounts (not possible I know but theoretically) you would have tremendous
leverage on the welds brackets and pivots.
But if the rear trailing arm pivots where on the axle centreline there would be no twisting moment at stand still apart from the weight of the diff
nose.
This could be cobblers but it looks as though the more offeset the more unneccesary strain.
Also with the very unequal length bars the axle may rotate as it rises and falls ,instead of working like a parrallelogram.
If you have little suspension travel this would not effect much, but then you've got to worry about your haemmorroids!!!
Or you could put the original mounts back and cut a step out of the 2 x 1 for the lower 8" or whatever it needs, it wouldn't take longto
cut out with a grinder then weld side back in with some 16swg mild steel back to 1" square.
[Edited on 9/2/04 by Surrey Dave]
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Stu16v
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| posted on 9/2/04 at 07:30 PM |
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Ned, the axle side is exactly how my modified Dax dedion and trailing arm setup is, but my trailing arms are equal length, rather than one long, one
short as in your piccy.
I will do my best to borrow a camera and get some more photo's up ASAP....
Dont just build it.....make it!
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Bob C
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| posted on 9/2/04 at 11:35 PM |
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The unequal length trailing arms will make the axle (dedion part) pitch forward on bump and droop, I guess this means that braking forces will alter
the way the suspension works but bugadifino how! (accelerating forces don't apply as the diff is fixed). But your main problem is that if one
side moves and the other stays in the middle ITS TRYING TO TWIST THE DEDION TUBE - not good. Why not move the bottom pivot on the dedion bit forward
to maintain the parallelogram.
cheers
Bob C
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kingr
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| posted on 10/2/04 at 09:27 AM |
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I think what you've built there is a form of anti-squat. Without calculating what and how much effect this would have, I would strongly recomend
that you stick to more established methods. Bob C's point about twisting the de Dion tube is valid, and something you should be concerned
about.
Kingr
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ned
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| posted on 10/2/04 at 09:46 AM |
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Thanks for the replies, after a night of little sleep and heavy thought I'm gonna eat my hat and do as james suggests, move the 2x1 tube and go
back to the 'book' trailing arm setup. this should eliminate any unknowns and go back to a tried and tested arrangement.
the only nuisance is that the chassis was originally built that way then i chopped it about, oh and i had trailing arms and panhard rod that i let go
for £25! muppet!
Ned.
beware, I've got yellow skin
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Steve Hnz
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| posted on 10/2/04 at 12:08 PM |
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Ned, Even though the Caterham de dion set up uses a lower A arm setup the relative fore & aft lengths of their arms are much the same as your
sketch, ie short top link & longer bottom ones. Never heard anyone grizzle that they don`t work. Cheers, Steve.
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craig1410
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| posted on 10/2/04 at 01:04 PM |
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Ned,
I'd be very cautious about going this way as I think it could indeed create some twisting loads in the de-dion tube. Of more immediate concern
to me would be the rather weedy connection surface area between the de-dion "ears" and the axle.
Where would you mount your shock absorbers by the way? If you don't mount the shockers directly above the axle then you will get really nasty
twisting loads but with your arrangement the trailing arms are right where the shockers need to go. You would have to mount them inboard or outboard
of the arms.
Cheers,
Craig.
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Bob C
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| posted on 10/2/04 at 01:16 PM |
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Steve - from what you said, the caterham axle is held at 3 points - say in the middle at the botttom & at the top at the 2 sides or vice versa.
This is fine, no possible twisting can be applied. In contrast there is a potential for massive torques to be applied to the 4link system esp. if
stiff bushes are used. It's just giving the back axle the excuse it needs to fail in service......
Cheers
Bob C
PS this site does thing to the spelling of some key words...........
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blueshift
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| posted on 10/2/04 at 03:13 PM |
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quote:
Originally posted by kingr
I think what you've built there is a form of anti-squat.
I don't think so.. if the trailing arms angled up towards the front, pointing towards the centre of gravity, I think that would give you an
anti-squat effect.
I did think about an unequal-length trailing arm setup like this a bit ago as a thought experiment. If the hubs, or possibly one of the hubs, was
articulated on the axle (allowed to twist around the axle) but fixed by the trailing arms, if you built some angles into the hub mounting or the joint
with the axle you might be able to produce desirable toe and/or camber changes on bump and droop.
Just a random thought for you suspensionists to chew over.
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200mph
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| posted on 10/2/04 at 03:20 PM |
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quote:
Originally posted by Bob C
PS this site does thing to the spelling of some key words...........
bollox...
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craig1410
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| posted on 10/2/04 at 07:37 PM |
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Hi,
You won't get anti-squat unless your trailing arms are angled downwards from the chassis and then you will get massive oversteer from the
effective shortening and lengthening of the trailing arms in rebound and bump respectively which will in turn effectively rotate the axle by producing
toe-in on the wheel nearest the corner apex and toe-out on the outer wheel. The result is rear wheel steering in the opposite way to that which you
would tend to want.
AFAIK, one of the cardinal rules of trailing arm suspension design is to make your trailing arms level at ride height or even slightly angled upwards
away from the chassis. This will give neutral handling (or slight understeer if angled upwards from the chassis) and will make the car more stable. Of
course too much of this would spoil your fun but on a light car with plenty of power to weight a little bit of inherent understeer is probably no bad
thing and should help you to get the power down out of corners.
In my opinion, if you want anti-squat then IRS is the only real option and even then it requires very accurate measurement of the CoG of the car. You
would need to know in advance exactly where the CoG is going to be and then angle your suspension pivots so that they are co-linear with the CoG
longitudinally. If you don't know where the CoG is in the first place then you would need to build the car fully, then measure the CoG (needs
more than just corner weights to get the height of the CoG by the way) and then redo all the rear suspension mounts... The same would apply to the
front mounts for anti-dive which is probably more useful than anti-squat anyway as braking forces are usually higher than acceleration forces.
Cheers,
Craig.
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ady8077
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| posted on 10/2/04 at 10:43 PM |
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Hi Ned
Bit late to the chat, but have you thought of running the top trailing arm to the rear of the chassis? Like Sylva?
Just a thought
Adrian
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James
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| posted on 11/2/04 at 09:55 AM |
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quote:
Originally posted by ned
I'm gonna eat my hat and do as james suggests,
Bloody hell mate are you feeling ok?
James
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ned
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| posted on 12/2/04 at 09:46 AM |
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no, i feel very ill.
Ned.
beware, I've got yellow skin
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