suspension geometry

[siputmagic]

hi there...
what is the pros and cons between push rod and pull rod?
if i want to built suspension system for FSAE, which want is more suitable?

most of FSAE car use double wishbone system..
Why double wishbone?

thanks in advance

[siputmagic]

hi there...
what is the pros and cons between push rod and pull rod?
if i want to built suspension system for FSAE, which want is more suitable?

most of FSAE car use double wishbone system..
Why double wishbone?

thanks in advance

[RiNaZ]

for starters ...

http://fsae.com/eve/forums/a/tpc/f/125607348/m/27560258...126057945#2126057945 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/2756025845?r=2126057945#2126057945)

http://fsae.com/eve/forums/a/tpc/f/125607348/m/85710135441/p/1

http://fsae.com/eve/forums/a/tpc/f/125607348/m/12810059...10759831#90210759831 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/12810059831?r=90210759831#90210759831)

http://fsae.com/eve/forums/a/tpc/f/125607348/m/26810968...10178411#84610178411 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/26810968411?r=84610178411#84610178411)

[exFSAE]

I won't be a dick this morning.. quick answers..

Push rod and pull rod are equally suitable. Comes down to packaging constraints. Pull rod setups are nice in that they get the weight low, though it may be harder to get at and adjust springs/dampers.

Really it comes down to what packages best for YOUR car.

As for double a-arm geometry.. its light, easy to fabricate, gives you good options on wheel movement control, easy to do simple analysis on.

[Chris Lane]

Push and pull rods are simply different ways of solving the same problem.

Pull rod you can do in tighter spaces, but somewhat harder to achieve the rates you want whilst balancing packaging constraints.

Push rod is pretty free in design, but takes up heaps more room.

As for the suspension design, do whatever you feel will best fulfill your goals for the system. Plenty of teams have done very well with unconventional suspensions.... I seem to recall reading about a european team who won Design one year with a deDion rear axle setup. Probably not the best solution dynamically, but they thought about it and justified their decisions very well and therefore won the design event.

[John Grego]

Pull rods are a challenge because it is harder to get a 1:1 motion ration since the angle of the pull rod is usually shallower than push rods. This means that if you use a push rod you can make your A-arms smaller since it will transfer a lot more of the energy than a pull rod...also due to the angle. This could be a possible weight savings due to smaller bars and possibly smaller hardware.

Pull rods are much more difficult to package. There is "infinite" space on the top of the chassis but not very much under it. Plus, this is generally where the driver's legs like to go, along with steering rack and possibly ARBs. There's a lot going on down there.

But as long as you can justify your choice it doesn't matter. Good luck!

[siputmagic]

thanks for all the reply...

maybe i'll go with the conventional design...
but as for the damper and spring setup, what is the different between single and double shock absorber setup?

thanks in advance..

[FATMOUSE]

You mean like having a monoshock at one end of the car instead of a more traditional setup?

I'd imagine interesting things occurring regarding damping in roll.

[siputmagic]

i've seen it somewhere in lola website...
just want to know what the different/pros and cons between them....

[Chris Lane]

A nice and simple explanation of how a monoshock system works can be found in Allan Staniforth's book 'Competition Car Suspension', pp. 183-190.

ISBN 1 84425 328 7

Hope this is helpful for you

[siputmagic]

thanks chris...
will take a look and learn from that book...

any opinion, tips and tricks regarding on suspension system is welcome..

thanks in advance...

[exFSAE]

F BMW's run monoshocks.. not entirely sure why. Maybe a cost thing? Does, I suppose, let you run really different ride and roll rates, since the ride springs aren't contributing at all to roll. For a FSAE car.. meh.

If I'm not mistaken I believe Colorado State used (or still uses?) a monoshock setup. Could ask them how they like it.

But Formula Continental, Formula Atlantics, Formula Ford, Formula Nippon, ChampCar, IRL, GP2, Formula 3.. I believe all use either just 2 spring/dampers, or 2 + 3rdspring.

[RacingManiac]

I believe Formula Renault 1600 and 2000 also runs monoshock, though in a different arrangement to the Formula BMW cars(as opposed to using 2 bellcrank with a T-antiroll acting on the damper, it uses a shuttle bar anti-roll/rocker on a single damper)...and I've see some Formula Ford uses the same type of setup as the Renault car...

[TG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by exFSAE:
F BMW's run monoshocks.. not entirely sure why. Maybe a cost thing? Does, I suppose, let you run really different ride and roll rates, since the ride springs aren't contributing at all to roll. For a FSAE car.. meh.

If I'm not mistaken I believe Colorado State used (or still uses?) a monoshock setup. Could ask them how they like it.

But Formula Continental, Formula Atlantics, Formula Ford, Formula Nippon, ChampCar, IRL, GP2, Formula 3.. I believe all use either just 2 spring/dampers, or 2 + 3rdspring. </div></BLOCKQUOTE>

I believe CSU uses the setup that Claude presents at some of his seminars (at least the one I went to). They have a coil spring and linear damper for pitching and heaving and a torsion spring and rotary damper for roll.

I know some of the lightweight rear swing-arm designs in fsae have used a monoshock on the rear because you can't really have much chain drive misalignment anyways.

[Brett Neale]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Lane:
I seem to recall reading about a european team who won Design one year with a deDion rear axle setup. Probably not the best solution dynamically, but they thought about it and justified their decisions very well and therefore won the design event. </div></BLOCKQUOTE>

European? You're looking WAY too far afield there Chris... http://fsae.com/groupee_common/emoticons/icon_wink.gif

PS - it was Adelaide. 2004 and 2005 had DeDion and gear drive. The 2004 guys won Design.

[Chris Lane]

Ah that was you guys!

Wasn't THAT far away http://fsae.com/groupee_common/emoticons/icon_wink.gif

[siputmagic]

another question from me..
what is the motion ratio?

[Chris Lane]

You really need to pick up a suspension book and read it cover to cover.

I started out with Allan Staniforth's 'Competition Car Suspension', which is a great beginners book which explains all the major facets of a suspension system in simple and easy to understand terms.

Then move on to Milliken and Milliken's 'Race Car Vehicle Dynamics'. It is widely considered to be the 'bible' of our FSAE world, with very good reason.

[siputmagic]

thanks chris...
just got the competition car suspension system by allan staniforth moments ago..
will read and understand it....

anymore parameters need to consider?

thanks in advance

[Chris Lane]

lots more mate, you'll soon find out...