Suspension Design

[AndyP]

I would be VERY greatful if some of the tech`s out there could share some of their knowledge and give me some pointers on where to start when designing suspension,

In the past we (formula student team) have began by deciding on the track and wheelbase dimension, then moving on to the length of the wishbones then proceeding from there. Is this right???

Also what about unequal wishbone lengths - is this a good idea and why?

Thankyou, Regards

Andy

[Matra et Alpine]

I would be VERY greatful if some of the tech`s out there could share some of their knowledge and give me some pointers on where to start when designing suspension,

In the past we (formula student team) have began by deciding on the track and wheelbase dimension, then moving on to the length of the wishbones then proceeding from there. Is this right???

Also what about unequal wishbone lengths - is this a good idea and why?

Thankyou, Regards

Andy

Andy, as much as we'd like to help, you've just asked for a complete year of an automotive design course as one post in an on-line forum

Anyway ....
track and wheelbase are as good a place to start.
BUT there is a first question and that is PURPOSE.
What is the car for, what do you woant it to do, what performance, handling, comfort over waht surfaces.

There are some excellent books on sports car suspension design and some have been copied onto peoples web sites ( quoting it as 'theirs' in many cases ). Unfortunately, mine are all out at friends who's been looking at adjustments for his 7-copy for track.

We've had a couple of the online ones quoted in other threads on UCP, but I can't find them quickly. You may want to do a search of the forums and spent a wee while reviewing.


Happy to try best to answer specific questions

On unequal wishbones, the benfit is the way the camber of the wheel caries over the movement of suspension. So you can use this in conjunctino with body roll to present a more stabel tyre contact location with the road. As the contact point varies it alters the car handling and resistance. Also by offsetting the wishbone pivots, you can also make anti-dive characteristics under braking.

Best advice I can give ( beyond reading the many books available ) is to use modern tools to better grasp the concepts and effects. So do all the design in a 3d engineering CAD package where you can move the elements and they will pivot/rotate as they would in real. Used to have to do this with drawing boards consider yourself lucky !!! So you can play with geometry and mounting and see how suspension movement affects wheel orientation, location and contact with the road. Egg-Nog has shamed me in the engine stroke posts with my lack of pictures. So I'll see what I can manage to help illustrate

[KnifeEdge_2K1]

i didnt even bother reading matra's novel like response ill just add my two cents

the longer the wheelbase the more stable the ride at speed, cornering is dif though because it will put more stress on the tires

err, double wishbones (parallel and equal length) give perfect camber control under bumpy conditions (up down motion) while under body roll experienced through cornering the camber will change at the same rate as the body roll angle

double wishbones (unequal and non parallel) give near perfect camber control under cornering, outter wheel which experiences most cornering "force" will retain near initial camber while inner wheel will have small change in it (of course this will depend on the length the angle and the mounting point

macpherson struts are cheap compact but not very good in terms of handling

chassis rigidity and design ... im not even gonna go here

its a really difficult topic to go over in just one thread, there are hundreds of variables which affect a cars cornering performance, ride, steering tendency (under/oversteer)

[Matra et Alpine]

See http://web.umr.edu/~formula/library/...per/paper.html first thing I found in a quick online search. Sounds like Missouri have done the work for you

You could try writing to local distributors of CATIA or ADAMS software. See http://www.mscsoftware.com/assets/27...ZSUPZLTDAT.pdf for what you coudl do BEFORE welding or bolting anything and http://www.mscsoftware.com/products/...ail.cfm?PI=413

Still haven't had time to come up with "Egg-Nog drawings"

[AndyP]

Many thanks to the people who`ve responded so far as I know its a diffiicult subject, esp to cover in one thread!!!

[Cyco]

There are some very good packages available for short term download that will help with pivot placements, and can calculate the roll/squat/dive characteristics. I don't have the link on this computer, but AFAIK many of the F Student cars run full rigid as they are no bigger than carts.

If you want to score some technical innovation points try throwing on something cool like the front diff arangement BAR got prevented from using at the Hungarian GP.

[byronleehk]

Check out the Bose hyperbolic suspension system for more ideas

[Matra et Alpine]

Check out the Bose hyperbolic suspension system for more ideas

MacPherson strut - not ideal

I reckon the guy in the first clip should win an Oscar for his acting.
He's clearly NOT trying to control his body movement and i think he's even tryign to make it look worse. his last pitch sidewyas is in anticipation of a bump that's not there. I smell a marketing hype

Also, HIGHLY unliekly that they can dissipate the heat generated by a linear motor durign hard use. Lotus played with this decades ago and heat dissipation was the MAJOR issue in any technology. I reckon it might well appear as a suspension augmentation but don't see how they can beat the laws of physics to make it viable as the only suspension.

Interesting though, thanks for the link.