Question abaout safety factors on designing suspension.

[Ivar Revolve]

Hi.
We are a new fs team and need some advice.

On pats corner I see that a thumb rule says 3g bump in a 2 g corner.
Does this mean that each and every corner on the car should be designed for this; considering wheel load transfer.
I imagine a worst case where only one wheel is touching the asphalt, maybe after a bump/hump in the road, or hitting cerbs (when we participate on baltic open)
Then this wheel, in that instant moment must take all the cornering and weight forces, if im not wrong.
Should we design this way or will it be too much?
Thank you http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Ivar Revolve]

Hi.
We are a new fs team and need some advice.

On pats corner I see that a thumb rule says 3g bump in a 2 g corner.
Does this mean that each and every corner on the car should be designed for this; considering wheel load transfer.
I imagine a worst case where only one wheel is touching the asphalt, maybe after a bump/hump in the road, or hitting cerbs (when we participate on baltic open)
Then this wheel, in that instant moment must take all the cornering and weight forces, if im not wrong.
Should we design this way or will it be too much?
Thank you http://fsae.com/groupee_common/emoticons/icon_smile.gif

[OspreysGoSWOOP]

I would say pick up a copy of a vehicle dynamics book and read about wheel loads. I reccommend Race Car Vehicle Dynamics by Doug Miliken or

Vehicle Dynamics: Theory and Application by Nakhaie Jazar.

This will give you a more accurate understanding of the forces your vehicle will experience during motion and should help answer your question.

[thewoundedsoldier]

Loads will only react to suspension components if the tire maintains grip. If you ask one single tire to react all vehicle dynamic forces, it is going to slip. This means your suspension components will not, at that point, be carrying such high combined loads.

Both TTC and previous competition results (skidpad and acceleration) will give you a good starting point with cornering and braking, and bump comes down to your level of comfortability with your design. I would say that 3g bump, 2g cornering, and 2g braking is pretty bulletproof for a starting team. Better to be too strong than too weak (this coming from me, a huge minimalist! http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif ).

[Dash]

it would also be beneficial to see if you need to do combined loading. doing each loading separately may or may not be the real case scenario.

[Adambomb]

The friction circle is your friend...

[The AFX Master]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Adambomb:
The friction circle is your friend... </div></BLOCKQUOTE>

Friction circle won't quite answer transients (bumps).

A pretty straightforward way to determine such loads is to model a quarter car with a critically damped damper. The real car will be designed around such numbers.

Then, solve the system using a ramp or step function mimicking a kerb or sudden expected surface irregularity. You'll realize that impact loads come from damping and inertial considerations.

For instance, lower sprung masses combined with softer high speed damper settings will result in lower loads.

[exFSAE]

Or just grab a beer, figure what kinda load cases will pick a wheel off the ground, run your FEA... ignore the FOS = 0.97 thing and roll with it.

That dog'll hunt.

[The AFX Master]

FEA while being drunk... Nice stuff.

Wonder if that qualifies as a Dynamic Analysis.