Steve Hnz
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| posted on 8/6/04 at 12:19 PM |
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Inboard front suspension
I`ve started coming around to the idea that inboard front suspension might be the way around what I see as the hassles of using standard shocks,
probably GTS, with wide track front suspension & still keep a reasonable shock angle etc.
& cause I think it would be a cool way to go!
I`ve got a lot more figuring out to do but hoped to use a similar system to the inboard Caterham prototype & the Fraser cars that are made
in NZ, a very superior 7 clone by the way. I`ve looked at the archives for info but some questions remaining are:-
How do I work out the wheel travel to shock travel for a given pushrod angle. I`m OK with the idea of the ratios for the length of the pusrod to
shock rocker ( probably use 1:1), & OK with whats required to make sure the shock works as linear as possible but rising rather than falling rate.
But my high school trig does not run to vector diagrams to be able to calculate wheel travel against shock travel for a given pushrod angle &
mounting distance. ( As close to the lower ball joint as possible) Can anyone recommend a suitable book on the subject. Any & all other input
greatfully received. Cheers, Steve Hannah.
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timf
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| posted on 8/6/04 at 12:48 PM |
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darren at gts used to do an inboard shock set up if you email him he may have some info available
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white130d
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| posted on 8/6/04 at 12:54 PM |
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Inboard shocks
Bob MacLeod did this....
Info can be found here:
http://www.7builder.com/7builder/BobsLocost.html
I think it would be a great way to do the front suspension too.
David
"There's only 2 things that money can't buy, and that's true love and home grown tomatos" Guy Clark
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Steve Hnz
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| posted on 8/6/04 at 02:10 PM |
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I have a copy of the PDF that Darren used to do, a nice set up but still out on it, Bobs one is another I`ve seen, would like to be able to mount the
rockers ( for want of a better name ) under the top rails( I`m going 1" higher as it is) & from what I can see his Rocker set up gives
falling rate, I`ve been led to believe this is undesirable. Comments? Keep it coming please. Cheers, Steve.
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pbura
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| posted on 8/6/04 at 02:19 PM |
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Allan Staniforth published a chart and some equations in Race and Rally Car Source Book, for translating wheel movement to pushrod or shock
movement. He credits the mathematicians who prepared the formulas, but doesn't use the equations for any examples, and instead refers to the
chart.
The inboard end of the pushrod will move by approximately the vertical movement of the outboard end multiplied by the cosine of the angle of the rod
from vertical, but because both ends are actually traveling in arcs, this is not quite the whole story. For planning purposes, using the cosine or
Staniforth's chart are OK, but IMO it's best to draw up the layout and move it through bump and droop to determine the actual ratio of
shock movement to wheel movement. This will flush out any errors you might make in calculating leverages.
If you buy a book, I understand that Competition Car Design has everything that's in the one I cited, plus more.
HTH
Pete
Pete
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MikeP
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| posted on 8/6/04 at 02:21 PM |
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Aren't Darren's shocks designed to give the correct damping when set at the angle and leverage for the book geometry?
I never tried to determine the rate change on Bob's set-up - how did you figure it out? The only way I know is to do drawings moving the wheel
a set distance in steps checking whether the compression at the spring side increases or decreases with each step. I don't think I gave enough
info for that  . An approximation with simple geometry might work, but small errors can cause bigger mistakes im my experience.
I can send you the drawings and measurements I have if you'd care to draw it up and let us know - it's a lot of work .
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JoelP
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| posted on 8/6/04 at 03:27 PM |
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its a nice set up in davids photo, but you might have some trouble getting it under normal noses. im sure you could fiddle the angles to make it
rising, falling or fairly constant.
i solved the shallow angle problem (if it counts as a problem) by moving my top shock mounting point out about 3 inches. it cost me some extra weight
to brace it but the shocks are now more upright and as close to the lower ball joint as i could manage.
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ned
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| posted on 8/6/04 at 03:35 PM |
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what's to stop you turning the top wishbone into a rocker like the st phoenix etc uses and mount the shocks i a similar position on th middle
like the pic? are there limitations due to the balljoints used on a locost? ie do you really want to be loading hte top transit joint, is it up to the
job?
another 7 thats uses inboards at the front is the quantum.
http://locost7.info/files/suspension/QuantumExtremeFrontSus.jpg
Ned.
[Edited on 8/6/04 by ned]
beware, I've got yellow skin
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ady8077
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| posted on 8/6/04 at 04:01 PM |
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Hi
My Stylus uses a simple rocker system, seems to work ok
Adrian
 
Rescued attachment Stylus rocker.jpg
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JoelP
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| posted on 8/6/04 at 08:52 PM |
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note the sturdy and short upper wishbone, on a convential sevenalike the upper bone is longer, hence more bending stress on it. it would have to be
very sturdy, which would adversely affect the unsprung weight.
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ady8077
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| posted on 8/6/04 at 09:06 PM |
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Hi
I think the Strikers rocker is the same ? but it does have a narrower front track
The Fury's rocker has been redesigned and is supposed to be alot stronger without adding more weight
Adrian
 
Rescued attachment rocker
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Steve Hnz
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| posted on 9/6/04 at 10:55 AM |
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Thanks for the replies so far.
Ned & Adrian, I want to stay with roughly book type wishbones in the interests of lightness & ease of fabrication. After the recent posting
re bent wishbones, I`ve firmed up on the idea of going with bottom wishbones with press in ball joints ala Caterham, easier to get the bottom
shock/pushrod mount closer to the ball joint, another reason to go with a pushrod operated inboard setup, less bulk.
MikeP, hope it didn`t sound as though I was bagging Bobs setup, I think they`re great, & a prime bit of inspiration for me. I`ve seen them b4.
By my own definitions I must say I was wrong re Falling rate, looking at the picture David posted, it should be rising rate. ( If the shock axis &
shock top mount /rocker pivot axis are <90deg then rising rate should occur is my understanding) & this is certainly true of Bobs design.
Pete, I`ll draw it up & work out the angle, thanks for that & the book recommendation.
Joel, I thought of going the way you went but came back to the idea of "liking " the thought of inboard suspension. I`ll put some thought
into it. Cheers , Steve.
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ned
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| posted on 9/6/04 at 11:07 AM |
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Steve,
Let us know how you get on with your design.
Though can anyone answer my question about whether the top transit link could cope with being under load from top rocker type wishbones. I am very
interested in the way quantum do the inboard on their car, it just seems so simple and with little modification to a book chassis or wishbones.
(link in revious post above to pic quantum extreme suspension)
Ned.
beware, I've got yellow skin
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ChrisW
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| posted on 9/6/04 at 11:07 AM |
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Using the top wishbone as the rocker seems the easiest way forward to me but did you notice neither of the cars in the pictures used the transit tie
rod as the top ball joint which makes me wonder if it's up to the job.
Chris
My gaff my rules
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ned
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| posted on 9/6/04 at 11:18 AM |
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would be interesting to find out what the quantum uses for an upright and top joint.
Ned.
beware, I've got yellow skin
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Spyderman
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| posted on 9/6/04 at 11:45 AM |
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If your trig isn't up to scratch then you could always try the Staniforth method.
Make up your own string computer!
A simple mock up in cardboard should give you enough information to be able to work most things out you need.
I've always found seeing things working as opposed to the calculations helps my understanding better.
At least by using cardboard or MDF you can experiment a bit more than you could with the chassis.
You only need to do it in two dimensions as well which should help understanding it easier.
Spyderman
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white130d
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| posted on 9/6/04 at 12:15 PM |
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Ends
Correct me if I am wrong, but aren't ball joints placed under compression loads, pushing the ball into the socket, not pulling it out. The only
time the joint is pulled is when it is unloaded, as when jacking the wheel off the ground or going airbourne. Even then the load should be ~ 50% since
it is distributed between the upper (pulled) and lower (compressed)ball joints. So is the transit upper joint up to the task? I would think so.
David
"There's only 2 things that money can't buy, and that's true love and home grown tomatos" Guy Clark
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Steve Hnz
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| posted on 9/6/04 at 12:18 PM |
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I looked at various designs & none of the top lever ones use a transit type ball joint, its really just stressed for push/pull type loads TMWOT. I
can see some 1"x1" timber & bits of MDF coming to the fore soon, I`ll try to master the intricacies of putting pics on here & post
a couple of sketchs of where i may be heading. Cheers, Steve.
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Steve Hnz
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| posted on 9/6/04 at 12:36 PM |
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David, they press in from below. The forces in a book suspension setup are trying to pull the lower ball joint apart. For this reason its important to
use a ball joint stressed for this ie one fron a similar double wishbone application. Its not to say others won`t do it , witness the common use of
Maxi ball joints & though I`ve not worked it out they`re `sposed not to be correctly stressed. Maybe someone forgot to tell them this. Caterham
use this type of press in ball joint for their units & Fraser here in NZ use Triumph 2000 ball joints in their Cortina uprighted models. The T2000
is a Mac strutted car & strictly this should be the wrong application but Neil Fraser has n excellent reputation as an engineer & builder so
I`d pick that he`s did his homework.
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white130d
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| posted on 9/6/04 at 03:08 PM |
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Tension
So the bottom ball joint will be in tension by the amount of the spring rate? say 220# if you use a 220# spring? Or there abouts..
David
"There's only 2 things that money can't buy, and that's true love and home grown tomatos" Guy Clark
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chbright
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| posted on 9/6/04 at 05:41 PM |
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i like these ideas, but all of them use springs, why not go for something waaaaaaaaaaaaaay out there.
like torsion bars
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JoelP
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| posted on 9/6/04 at 06:12 PM |
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quote:
Originally posted by white130d
So the bottom ball joint will be in tension by the amount of the spring rate? say 220# if you use a 220# spring? Or there abouts..
David
the full weight of the car is hanging off the balljoints. essentially each of the front ones in a normalish 7 situation will have between 150 and
200kgs hanging off each. thats quite a lot of stress for it to cope with.
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Steve Hnz
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| posted on 9/6/04 at 09:23 PM |
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quote:
Originally posted by chbright
i like these ideas, but all of them use springs, why not go for something waaaaaaaaaaaaaay out there.
like torsion bars
While its a nice idea & elegant engineering ( Jaguar Cs, Ds Es etc) I`m trying to do something that does not involve too much reengineering of a
book style chassis. In my mental concept, the basic front frame & suspension mount points are retained with only minor adaptations to mount
rockers & spring bases . Refer back to MikePs post & have a look at what Bob has done. This gives some idea as to how it can be done to go
inboard without radical redesign. Cheers, Steve.
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ady8077
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| posted on 9/6/04 at 09:52 PM |
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Hi
I dont think the bottom ball joint is taking any of the cars weight on my Stylus, I can remove the bottom wishbone whilest the tyres are still on the
ground. I think the top ball joint is off a metro and threads into the Sierra upright Quinto Hazel No. QSJ 1060S
The Sylva style of rocker has been very succesfull in motorsport and by removing the spring from the bottom wishbone it must improve aerodynamics too
?
Adrian
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JoelP
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| posted on 9/6/04 at 09:59 PM |
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i couldnt make any comment about a stylus cos i've never seen one, but my comments apply to books style front suspension. How does the stylus
one work? is it a top rocker?
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