Springs and Damping

[The Stigg]

Hi Guys,

as springs and damping is the next big chapter on my to do list I started with some basic calculations like the ones posted by Z in this post.
http://fsae.com/eve/forums/a/tpc/f/125607348/m/90210283...10704521#19710704521 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/90210283521?r=19710704521#19710704521)

Now I'm wondering about the Stiffness K.
In this example only tyre and corner spring are considered.
Shouldn't it be the complete wheel rate with all influences from ARB and if present a third spring?

Andy

[The Stigg]

Hi Guys,

as springs and damping is the next big chapter on my to do list I started with some basic calculations like the ones posted by Z in this post.
http://fsae.com/eve/forums/a/tpc/f/125607348/m/90210283...10704521#19710704521 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/90210283521?r=19710704521#19710704521)

Now I'm wondering about the Stiffness K.
In this example only tyre and corner spring are considered.
Shouldn't it be the complete wheel rate with all influences from ARB and if present a third spring?

Andy

[blister]

Hey Andy, (are you the wagner andy?)

The topic you posted has mainly good points about mountain bike shocks. For the calculation of the additional stiffness of a third spring the tech tips on optimumg.com are very helpful.
3rd springs are very interesting...

So you are doing a third year in FS?

Greets, Urs

[The Stigg]

Hi Urs,

no I'm alumni and writing my diploma thesis right now but I'm still interested in vehicle dynamics.

I know about the tech tips, but this is not the answer to my question. As I pointed above I think you should calculate the damping ratio and the motion ratio for the wheel bounce mode (single wheel bump) with all reacted springs !?

For example MR=1:1
Car details:
=============
Wheel Assembly = 15kg
1/4 Body = 50kg
Kspring = 20 kN/m (~20 kg/cm)
Ktyre = 130 kN/m
Karb = 10kN/m
MRarb = 1:1
K3rd = 5kN/m
M3rd = 1:1

Wheelrate Spring Ks = Kspring*MR^2
Wheelrate ARB Kr= Karb *MRarb^2

So;
Wheel rate for
Kbody-bounce = (Ks x Kt)/(Ks + Kt) + K3rd*MR3rd^2 = 22 kN/m (springs in series)

Kwheel-hop = (Ks + Kt) + Karb*(1/2MRarb)^2 + K3rd*(1/2MR3rd)^2 = 153,75 kN/m

Andy

[exFSAE]

You answered your own question.

Yes. Anything that acts in "X" suspension mode.. should be accounted for.

[Mark_W]

it depends which mode of suspension movement you want to calculate your stiffness and damping for.

For pure ride, ARB's are not active and should not appear in your calcs. In roll they are, and so on and so forth...