Ground Friction and Resistance Index

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jhdm17
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Re: Ground Friction and Resistance Index

Postby jhdm17 » Sun Dec 20, 2009 11:09 am

i have downloaded notepad and saved it still doesnt seem to work

do i have to add "@trackname/texturename.ppm" at the end of it?
thnx

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yzmxer608
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Re: Ground Friction and Resistance Index

Postby yzmxer608 » Mon Dec 21, 2009 6:45 am

Make sure not to save it with a file extension, it shouldn't have one. It's just a plain "file".
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Re: Ground Friction and Resistance Index

Postby iceman967 » Wed Dec 30, 2009 1:59 am

Now this may not make sense but once I release the track youll see. I am looking for a fairly slippery surface for the tileinfo. Like off track stadium floor slippery. Any help is greatly appreciated! thanks guys.
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Phathry25
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Re: Ground Friction and Resistance Index

Postby Phathry25 » Wed Dec 30, 2009 2:10 am

start low and it should drop off as slip gets higher

On a JLV related note...What kind of tire modeling is done? What model does it use. Should we be using the ground friction more as a traditional pacejka slip curve?

jlv
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Re: Ground Friction and Resistance Index

Postby jlv » Wed Dec 30, 2009 3:44 am

It's coulomb friction with the coefficient varying by slip rate. I don't use different coefficients for lateral slip.
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Phathry25
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Re: Ground Friction and Resistance Index

Postby Phathry25 » Wed Dec 30, 2009 9:39 am

jlv wrote:It's coulomb friction with the coefficient varying by slip rate. I don't use different coefficients for lateral slip.


I'm a dummy so please bare with me...

So the tires have the same amount of grip on both axis? (lat/long) Or do they just share the same coefficents? Is there any sidewall/air pressure simulation?

IMO to properly simulate different types of dirt you would need to control the lat and long slip of the tire separately. I say this because in loamy soil or sand you'll slip on the longitudinal (word?) axis more quickly and aggressively then you will on the lateral axis. For hard-pack I would guestimate the current matching slips would be near accurate. I'm going with my assumption above that both axis have the same amount of grip here... having both axis have the same amount grip is wrong isn't it? The lug is wider than it is in length, thus more area to create friction. And the front should be different as the lug shapes are different...

Also what is the maximum slip that can be achieved? 90 degrees right? Is that 90 in the tileinfo?

It's late and I'm trying to keep my mind off of other things here, feel free to put me in my place. :D I just like knowing whats happening so I can manipulate it to my needs as best as possible... TIA!!!

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DJ99X
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Re: Ground Friction and Resistance Index

Postby DJ99X » Wed Dec 30, 2009 9:43 am

For starters, how is the area different for both dirrections?

Secondly, area isn't even a factor with friction.

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Re: Ground Friction and Resistance Index

Postby jlv » Thu Dec 31, 2009 12:15 am

It would make sense for a tire that digs into the dirt. In that situation a ribbed tire would have more lateral friction than a paddle tire. For knobbies I doubt it will be very different.

Phathry, one thing you might be missing is that MX Simulator uses extra bodies to model the wheels and suspension parts, so a lot of those tire formulas used in 1 body car sims don't apply.
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Phathry25
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Re: Ground Friction and Resistance Index

Postby Phathry25 » Thu Dec 31, 2009 10:29 pm

Could you explain the extra bodies comment? I'm not following you, like I said I'm stupid.

DJ. If surface area has no effect on friction why does my bike hook up better on a blue groove with lower tire pressures so I can put down a bigger footprint?

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DJ99X
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Re: Ground Friction and Resistance Index

Postby DJ99X » Fri Jan 01, 2010 12:01 am

I was going off this equation

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Re: Ground Friction and Resistance Index

Postby jlv » Fri Jan 01, 2010 12:47 am

Phathry25 wrote:Could you explain the extra bodies comment? I'm not following you, like I said I'm stupid.

You can leave the wheels off the car and figure out approximately what forces the wheels would have put into the frame of the car. That way instead of having 5 bodies (the frame and 4 wheels) and lots of suspension joints you only have one body for the frame. It would save a huge amount of processing time. (You still draw the wheels of course. They just aren't part of the constraint equation.)

MX Sim doesn't do that. The wheel inertia is too important to leave out for a motocross bike simulation.
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Prologue
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Re: Ground Friction and Resistance Index

Postby Prologue » Mon May 17, 2010 5:14 am

Phathry25 wrote:Could you explain the extra bodies comment? I'm not following you, like I said I'm stupid.

DJ. If surface area has no effect on friction why does my bike hook up better on a blue groove with lower tire pressures so I can put down a bigger footprint?


The lower pressure tire conforms to the surface better and is in contact with the ground for a longer time on average. When there are little ripples in the surface of a track, the lower pressure tire gets indented, wraps around them and on average is in contact longer than if it was way pumped up, so you get better grip. Also, the lower pressure tire has a lower resonant frequency (the frequency at which it wants to vibrate, like if you hit it with a hammer) so in certain circumstances it can keep itself on the ground by vibrating correctly.
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Re: Ground Friction and Resistance Index

Postby JB323 » Thu Jun 17, 2010 5:10 am

----All around tacky dirt--------


friction 0.7 1.5
friction 1.2 3.0
friction 1.2 4.0
roll_resist 10 20 0
roll_resist 20 30 20

used on lastest tracks released, Glen helen, MissionValley and Sorento, After lots of testing the whole xfire crew pretty much agrees this is the standard for "perfect " dirt. it holds you up enough to corner aggressively, while letting it slide and wash out. Hope it helps some people to help create great tracks as we are.
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Re: Ground Friction and Resistance Index

Postby jlv » Thu Jun 17, 2010 10:36 pm

friction 0.7 1.5
friction 1.2 3.0
friction 1.2 4.0
roll_resist 10 20 0
roll_resist 20 30 20

The third line is superfluous. Since the friction is 1.2 at 3 feet/sec of slip, there is no need to set it again at higher slip speeds.
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Re: Ground Friction and Resistance Index

Postby Duckstream » Thu Jun 24, 2010 5:46 pm

anyone got a good set for like grass and mud (not MUD MUD but like gravel) that is bit moysterois... (typo?) like after rain but Not too splipery,
making a enduro track so thats why its have to bee something that feels like when riding while fog in air in the woods in grass paths....or something..


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