rec.autos.simulators

Huh what? ;-)
According to my own site the conversion factor from ft*lbs^2 -> kg*m^2
is 1.3557. That would give 12.160629 kg*m^2.
My Ferrari 312 has... hm... 2.3. That does seem a bit low. Any idea
how much that tire of yours weighed (in slugs for all I care, lol)?

I think that number was once based on a formula for the inertia of a
cylinder with all mass around at the edge. Can't find the URL of a
great page on this I once used.

I implicitly integrate my wheels, and that seems to kill some wheel
hop effects. Or at least, I can run a 200,000 N/m suspension and
300,000 N/m tire spring combined at 250Hz and it's stable (haven't
really dug too deep in the option I have to use suspension forces as
load vs. using the real tire normal force).

Hehe, in Holland, we have few hills. We don't need to relax tires
here. ;-)

Ruud van Gaal
Free car sim  : http://www.racesimcentral.net/
Pencil art    : http://www.racesimcentral.net/

But at least you know I don't trust that conversion factor anymore.

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

Something's wrong Ruud - you can't convert ft*lbs^2 to kg*m^2 can you? Units
are different. You'd need to convert from lb*ft^2......

Jim

Having thought a little harder.......

    1 lb*ft^2 = 0.454kg x (0.3m)^2 = 0.04 kg*m^2.

    8.97 lb*ft^2 is therefore around 0.36 kg*m^2, not 12.160629.

I've not taken many significant figures through this, and I'm hoping my
rather rusty maths is holding up!

Cheers

Jim

So that 8.97 would become ~ 0.378.
But that uses lbs*ft^2, NOT ft*lbs^2, which would make more sense
since that looks a lot more like kg*m^2.

Still, 0.378 seems very LOW to me intuitively. ;-)

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

1 lb = 0.45359237 kg
1 ft = 0.3048 m

lb * ft * ft = 0.042140110093804806

1.3557 seens frighteningly familar, though I can't remember why.
1.3557 * 2 = 2.7114 --  isn't that some sort of natural number?

btw; aren't you a unix man, Ruud?  

Gunnar, hinting of man units
--
Gunnar
    #31 SUCKS#015 Tupperware MC#002 DoD#0x1B DoDRT#003 DoD:CT#4,8 Kibo: 2
             "a poster is a human being or the software equivalent"

As some units have strange counterparts (a Joule has some funny
representations) I became confused.

Yes, the original units given though were ft*lbs*lbs, and take with
the fact that the US units don't use mass but weight preferably, this
was enough to make me lose my balance. :)
lbs and lbf are two different things, right; one is a weight, the
other one a mass more (like slugs). Perhaps I'm just confusing things
further here though by stating that. ;-)

Mostly Unix, but also Windows, and a hint of the Amiga not too long
ago. Is Unix 2.7114 as good as Windows? ;-)

And as XP is really going the wrong route (IMHO), Linux and such get
more and more interesting. The KISS principle is something which
obviously hasn't been adapted by Microsoft's designers, when needed
most.

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

-Gregor (who hasn't checked in for a while, but just might do so more
regularly soon enough)

Sigh, I venture onto a Car Physics thread and get totally ignored despite
posting the correction several hours earlier than anyone else. Ah well I'll
go back to loitering on the Racer forum then...

<g>

Jim

You should. It's good to have you in here. :)

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

  Whoops!  Sorry about the confusion, I meant lbs*ft^2, not ft*lbs^2...  Or was
it slugs?   Hmm...  Well, whatever polar moment of inertia is accelerated at 1
rad/sec/sec when 1 foot-pound of torque is applied to it anyway :0)

  I don't know how much the tire weighed, although it was from a small car...
This should have been a rather low polar moment tire, but was still much higher
than what I'd been using previously (by about 3-4 times usually.)

  That's pretty good, what was it before you went to implicit integration?
Have you tried this in the rotational direction yet?

  lol  If you're a Racer driver, you never relax your tires either :0)

Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com

My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm

Must have been that yes. And the 12.16 isn't right; it's more like 0.4
in kg*m^2, it turned out. That's a blow for the sim frequency. ;-)

Over a 1000Hz. Unfortunately my smallest timestep IS 1/1000s, so
actually it just did not work, lol.

Nope. Might be an idea indeed for low-speed operation. Have to get a
look at this one time. For low-speed only ofcourse; you quickly can
move to the usual integration.

So true. :) We had a kart race yesterday, with 8 karts, of which 4
were replaced during the qualifying sessions. Those tires also
probably didn't have a relaxed time there. :)

Ruud van Gaal
Free car sim  : http://www.marketgraph.nl/gallery/racer/
Pencil art    : http://www.marketgraph.nl/gallery/

  Yes, it is.. It turned out to be a good thing for me though, since I
underestimated the values by a factor of about 3.

  So....  How did you do the implicit integration, anyway?  This was only for
the vertical wheel motion, right?  I am still fuzzy about how this works..

  Great fun!  There's an indoor track nearby with carts that do about 70 kph..
Lots of fun on a tight concrete track.

Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com

My little car sim screenshots:
http://performancesimulations.com/scnshot4.htm