Having just implemented ARBs I have now noticed that the lateral
springyness (for want of a better word) has increased, I don't mean
stiffness but the wobblyness that is observed when increasing the
spring rate but not the damping rate.
Is this correct?
I am assuming that it is and therefore if ARBs are used and a loaded
corner hits a bump, the reaction is greater than if not using ARBs,
correct?.
Regards,
Colin
If you increase roll stiffness without increasing damping, then the
wobblyness (if I understand your technical term correctly ;) should
increase. And since ARB's increase roll stiffness without affecting
vertical or pitch motions, the damping that feels correct over bumps, or
during acceleration and braking, will no longer be adequate in roll.
Also with regards to a loaded corner hitting a bump, yes the reaction is
definitely greater when using ARB's, that is one of their drawbacks. So
what you are observing sounds correct to me.
"Colin Reed" <[email hidden]> wrote in message
news:[email hidden]...
Quoted text (13 lines)
> Having just implemented ARBs I have now noticed that the lateral > springyness (for want of a better word) has increased, I don't mean > stiffness but the wobblyness that is observed when increasing the > spring rate but not the damping rate. > > Is this correct? > > I am assuming that it is and therefore if ARBs are used and a loaded > corner hits a bump, the reaction is greater than if not using ARBs, > correct?. > > Regards, > Colin> And since ARB's increase roll stiffness without affecting
> vertical or pitch motions, the damping that feels correct over bumps, or
> during acceleration and braking, will no longer be adequate in roll.
So what you're saying is that cars with ARBs will have their damping
tweaked to account for this differing behaviour, yes?
> Also with regards to a loaded corner hitting a bump, yes the reaction is
> definitely greater when using ARB's, that is one of their drawbacks. So
> what you are observing sounds correct to me.
;-) Good, it is working then ....
On a completely different topic, does anyone have example figures for
(Doug?) :-
1) Ball joint locations relative to hub centre.
2) Unequal double wishbone lengths (upper and lower).
3) Approx wishbone locations in relation to CG.
4) Suspension locations with relation to either upper or lower arms
and the body.
I have all the above coded but am not sure how to setup the wishbones
properly, ie how much should the camber change with suspension
deflection, how much KPI and caster is good/bad.
Oh, and for anyone that is interested, I have switched over to MASSed
wheels with tire spring modelled, it was a natural progression of the
wishbone code that I was developing and I really wanted to be able to
(fairly) accurately model open wheel cars (when they are upside
down!), ie after flipping the car, I wanted the wheels to behave
properly when hit from above (or below because the car is now upside
down ;-)).
Anyways, thanks in advance for any help with those suspension offsets
...
Regards,
Colin
"Colin Reed" <[email hidden]> wrote in message
news:[email hidden]...
> > And since ARB's increase roll stiffness without affecting
> > vertical or pitch motions, the damping that feels correct overbumps, or
> > during acceleration and braking, will no longer be adequate in roll.
>
> So what you're saying is that cars with ARBs will have their damping
> tweaked to account for this differing behaviour, yes?
From a practical standpoint I am not sure how this is done (i.e.
specifically what percentage of critical damping is normal, and do you
calculate it only in bump or also in roll), but I do believe that
damping has to be a compromise between what is correct for bumps, what
is correct for pitch motions, and what is correct for roll motions. I
have noticed in sims that as I increase the size of the ARB's that the
car definitely gets more lively in roll. I usually try to trim this out
with rebound damping, and leave the bump damping alone. I believe that
is what was recommended in RCVD. In GPL for example I typically set the
bump damping according to the pitch behavior in braking and
acceleration, and then set the rebound damping as necessary to control
the rolling motions and the steer characteristics in transient
conditions. While this feels very comfortable to me, I am not a
particularly fast driver so I don't actually know if this is the best
way to do it or not.
Sounds really interesting. To me that is one of the coolest aspects of
this newsgroup - seeing all these "do-it-yourself" projects taking
shape. I haven't really gotten around to trying very many of them yet,
but I still find it fascinating. Keep up the good work.
Quoted text (9 lines)
> > Oh, and for anyone that is interested, I have switched over to MASSed > wheels with tire spring modelled, it was a natural progression of the > wishbone code that I was developing and I really wanted to be able to > (fairly) accurately model open wheel cars (when they are upside > down!), ie after flipping the car, I wanted the wheels to behave > properly when hit from above (or below because the car is now upside > down ;-)). >>On a completely different topic, does anyone have example figures for
Try this analysis program, it has some geometries included:
http://www.bevenyoung.com.au/suswin.htm
It might be interesting to other sim writers too. The help file has some
information on tire spring rates and so forth.
>Oh, and for anyone that is interested, I have switched over to MASSed
>wheels with tire spring modelled,
Doh!! How'd ya do that? Grr...! lol
Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com
My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm
> Try this analysis program, it has some geometries included:
> http://www.bevenyoung.com.au/suswin.htm
>
> It might be interesting to other sim writers too. The help file has some
> information on tire spring rates and so forth.
Thanks for the link, what an interesting program, I would really like
to see the roll and bump settings as slider bars, that way you could
see more of the dynamic effect, if you know what I mean.
> Doh!! How'd ya do that? Grr...! lol
;-) Strings and mirrors, actually it is not 100% physically accurate
and there are some extreme cases that are not handled properly (eg.
spring rest lengths is longer that possible suspension extension), but
it feels really right and having bump stops now is really cool ...
Colin
Slow newsfeed, this just in today <grrr>.
There are quite a few examples and simplified suspension calculation
methods in our new book, description here:
http://www.millikenresearch.com/olley.html
Our initial intent was to present Olley's material as a text book and for
use in checking detailed simulations. But I can see that many of the
simplified methods (originally calculated with slide rule!) will also be
good enough for most entertaiment simulators.
Just think, you get a summary of Olley's life-work and four years of our
work, for a mere US$ 79 <shameless plug!>. He ought to know how to
calculate an independent suspension -- he was the one that brought it
to mass production in the early 1930's.
-- Doug Milliken
On 19 Apr 2002, Colin Reed wrote:
......
