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.

darren at gts used to do an inboard shock set up if you email him he may have some info available

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

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.

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

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 .

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.

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]

Hi
My Stylus uses a simple rocker system, seems to work ok
Adrian
Rescued attachment Stylus rocker.jpg

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.

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

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.

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.

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

would be interesting to find out what the quantum uses for an upright and top joint.

Ned.

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.

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

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.

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.

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

i like these ideas, but all of them use springs, why not go for something waaaaaaaaaaaaaay out there.


like torsion bars

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

---

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

---

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

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?

Hi Joelp

I posted a pic on page 1 you commented on them ???

Top rocker and bottom wishbone

I reallised you were talking about locost wishbones but i thought i'd show the Stylus type because they look very easy to design, and do away with push rods and pivot blocks

Adrian

oops, at least i never claimed to have a good memory!!!!!

i remember now. thats a good way of doing it, provided you can make it strong. a good approach might be to make it trianglar. i wonder what the weight difference is? my personal favourite is the other picture with a pushrod and simple rocker.

This is how I made my push rod suspension. The actual push rod in the pic is a dummy. I've got some aerofoil tubing that I'll use instead.

I think I made six prototypes before I made one that will not only will work, but also fit inside the car...



Pushrod suspension 2

By moving the bottom fixationpoints of the shockabsorber, I can change the gear ratio from slightly progressive to linear.

[Edited on 10/6/04 by Gripenland]

Lotus 33 style rocker arm inboard suspension isn't worth the trouble - a lot of Formula Ford manufacturers tried it in the late 70s and then reverted to conventional suspension before push rods came into fashion. The loads it places on the chassis and top wishbone are way above anything seen in the book chassis and it isn't hard to get in a situation where the wishbone and chassis flex gives more suspension movement than the springs.

Push rod suspension is a different matter the chassis loads are still very high but they are easier to contain and decent rising rate suspenion comes free. However look carefully at the changes made to FF chassis design when push rod suspension came in vogue -- the front part of the spaceframe became much more complex with lots and lots of extra tubes.

An easier alternative is pull rod suspension which MacLaren pioneered in the early 70s.




[Edited on 11/6/04 by britishtrident]

i may be wrong, but i think steve graber is using pull rod suspension. his site is full of good stuff and pics.

I think britishtrident's last post has to be one of the best on this thread. Cheers!