[ODE] Re: Simulating Wheels

Steve Baker sjbaker1 at airmail.net
Fri Nov 7 08:54:02 MST 2003

Amund Børsand wrote:

> Well, long before that you have to get the center of mass correct for
> the chassi, as well as correct mass and inertia for wheels, springs,
> dampers, whishbones, spring struts, and positioning joints for the
> suspension in correct places.

Yep.  I know a guy who repairs and upgrades cars like the one I'm
simulating.  He's going to weigh the parts whenever he has the need
to remove them.  We know the dimensions of them and you can do a
reasonable job of estimating the inertia tensor by aggregating simple
shapes like cylinders and cubes for which the inertia tensor is well known.

> If you get that measured up correctly you
> WILL get a pretty realistic simulation... including all kinds of
> suspension goodies like variable camber angles and stuff. Combine this
> with Pacejka formulas, and a proper set-up steering rack and correct
> camber, caster and toe-in, feed the feedback from the steering rack back
> to a force-feedback steering wheel, and congratulations, you'll probably
> have the most realistic car simulator ever! :) (This is what I'm
> planning to do, don't steal my idea now :)

Well - I'm not sure it's an entirely original idea...but yes - that's
what I'd like to do.   I'd like to make that be an OpenSource project
with 'reasonable' defaults for most of the car parts to get you a working
car model "out of the box" - with the ability to put real world data into
it to simulate a specific car more accurately.

Then - people who want to make a car driving game can just dump that
code into their package and concentrate on the more interesting parts
of writing a game like plot-line, scenery, etc.

> Oh, check the ODE manual. It has formulas for converting SI units of
> spring rates and damping rates into CFM and ERP. That IS no problem ;) 

Yep - that's true.

> You can also find data on different springs and shocks on the net..
> however it's not very easy to find.

Do you have some pointers?   I couldn't find *anything*.

> (Just like how do you know the
> height of the center of gravity of your car? That's a tough one - which
> HAS to be correct to make the car handle correctly.)

Well, I know some of this data for my car.  The height of the CoG is in the
manufacturer's spec's (presumably because they are proud of how low it is...
that data might be harder to find for a roll-over-prone SUV)!

It's certainly important though.  I was greatly suprised by how much
more body roll there was in a friend's car - which is identical to mine
except for the sun-roof.   I later discovered that the sun-roof weighs
65 lbs - and it's the highest thing on the car - so it has a big impact
on the CoG height!

---------------------------- Steve Baker -------------------------
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