suspension design evaluation

[gryphon]

Someone please evaluate these results 4 suspension simulation.

FRONT
http://www.postimage.org/image.php?v=Pqcnyl0

REAR
http://www.postimage.org/image.php?v=aV1RWaqJ

<STRIKE>few doubts </STRIKE> few doubts
1.Is kpi of 12 and caster of 6 permissible?
1.When we place roll centre close to ground there is a huge lateral migration of the roll centre. Roll Eyes Can someone please enlighten me how this migration of roll centre will effect handling.
2.how do we decide relative height of front and rear roll centre. Confused I ve read that front roll centre is lower.Why?how do we decide this difference of height?
Is there some way to decide cog height at different transverse planes?

[gryphon]

Someone please evaluate these results 4 suspension simulation.

FRONT
http://www.postimage.org/image.php?v=Pqcnyl0

REAR
http://www.postimage.org/image.php?v=aV1RWaqJ

<STRIKE>few doubts </STRIKE> few doubts
1.Is kpi of 12 and caster of 6 permissible?
1.When we place roll centre close to ground there is a huge lateral migration of the roll centre. Roll Eyes Can someone please enlighten me how this migration of roll centre will effect handling.
2.how do we decide relative height of front and rear roll centre. Confused I ve read that front roll centre is lower.Why?how do we decide this difference of height?
Is there some way to decide cog height at different transverse planes?

[MalcolmG]

I started writing a big list of suggestions, but the more I looked the more very fundamental issues I saw with what you're doing, so I'm going to make some different suggestions:

*Read some books. RCVD by Milliken and Milliken, Tune to Win by Carrol Smith would be good starting points

*Think about the moments that are going to be created about your massively offset kingpin axes under longitudinal accelerations and cornering - these forces have to be reacted by either your toe links on the rear or your driver at the front, and I think both will have a very hard time with the values you have

*Forget about the CoG positions at multiple transverse planes along the car - your car will only have one CoG

*Have a look at the tunability of a suspension with drastically different roll centre heights front to rear: your front to rear roll stiffness distribution is a very important tuning parameter and you're going to need high spring rates/ARB stiffness in the rear to stop that car plowing

[gryphon]

please everyone pitch in http://fsae.com/groupee_common/emoticons/icon_smile.gif
Is there something like "if u keep your kpi double the caster you end up with negligible camber change"?
Can someone help me with olleys formula. though i found it somewhere but i believe that the math relation was wrong.

[Adambomb]

There is a fairly simple trig relationship between camber gain, KPI, and caster. Outside of that, ditto on Malcolm's recommendations.

P.S., don't expect everyone to jump in just because you've been re-posting the same post for the last 4 days. IMO that's bad etiquette. The few replies you have gotten are about the best you can expect for such a vague set of questions. Read up on it first, then think hard about it for a long time! That's what we all did.

[gryphon]

Hi!
though now i ve read tune 2 win but i didn't find the relationship.
and as suggested above i ll look into other books for the same.

[MalcolmG]

heck you don't even need to understand the relationship (although it is very simple), you clearly have a susprog model of your suspension so if you do a steering analysis it will tell you exactly how much camber change you're getting with steering. I'd also recommend you read Pat Clarke's article of advice for new teams, there's some good, basic design advice there to get you started. I think it's available on the FS Germany website

[Adam G]

You really need to sit down with your team and set up a particular overall design goal. You can't really start any detail design unless you know where the car as a whole is headed (not saying you haven't done this, just that you didn't mention it). For the past few years my team has been pushing weight savings very heavily, which drove our design to using a solid rear axle without a differential. Obviously, this had a drastic effect on how the rest of the suspension and vehicle was designed.


However, I do have a quick comment about your simulation results. How often will your car be going through a few degrees of roll without any steering input? Your simulation is not extremely clear, but it appears that you are simply looking at roll angle. I would suggest adding some steering angle into the simulation. How much steering? Well, that is something for you to figure out based on how well you think your car will behave. But it will take some steering input and slip angle from the tires before you can generate lateral grip and therefore have a roll angle. Just something to think about.

Otherwise, good luck figuring it all out.