How to Instant Center with parallel links ??

[Julien88]

I would like to design a Fourcross (a four wheel downhill mountain bike). If you don't know what I'm talking about go to the R-One website.

http://www.r-onefourcross.com/

My problems is I don't know how to find the Instant Center if my two links are parallel. I know that the instant center point is the intersection of the two projected lines of the links (the two A arms). But parallel links will never intersect...it's kind of weird and it's the only way I know to find the roll center.

Another problem I have in suspension geometry is the postion of the shock absorber. Do anyone knows any tips or theory (books, internet) that would helps positionning the shock absorbers. (fixing points, angle, travel) see the R-One fourcross front suspension for example. I don't know how or why this guy decided to fix his shocks absorber this way...what's the key to find a design that's better for our kind of vehicle?

If you have anwsers...please let me know
if you got another way to find the roll center point or any theory or good website on suspension geometry...
Thanks a lot for anwsers !!

 

[patprimmer]

4 cross.

When I was a kid we called them pedal cars.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

A ten thousand dollar pedal car at that.

Julien if you look in the FAQ there is a list of books.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Julien88]

yeah a ten thousand dollar bike and there is not even pedals on it!

Thanks a lot for the information Greg
and for the list of characteristic to...it will be useful

I bought Race Car Vehicle Dynamics...but my interrogation is
that I don't know how I'm gonna deal with the ''Race car''
theory for an off-road suspension geometry...?
Are the characteristics of geometry the same for race an Off-Road? I didn't find any books or good sources that talks especially about Off-Road suspension.

It is pissing me off...!

 

[GregLocock]

Yes, you can use the same principles. If you look towards the back of the book there are a couple of tables of interactions.

You are interested in things like straight line stability on rough surfaces, brake in turn, and so on.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[sreid]

For parallel suspensions links, the roll center is at infinity (as you have already seen). This always puts the roll center at ground level.