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Hard_Truck being weird with modified physics....
I've been modifying the .TXT for the Hard_Truck, mostly moving the rear wheels back so they're underneath the first set of wheels on the model instead of the middle of the frame, as well as raising the center of gravity and moving it back a little.

However, now I've run into a weird problem. With my current wheel positioning, I can't move the center of gravity farther forward than somewhere just ahead or under the 5th wheel, and I want to move it so it's about a foot and a half underneath the rear of the cab. However, when I try to do this, the truck gets all jumpy. The wheels start jitting upwards and eventually the truck is bucking around like a box with some insane kangaroo in it. It's even worse if I try to make the damping softer.

Do I need to raise the center of gravity so it isn't quite as "flat", change the suspension, what?

There are several cars with wheelbases longer than the one I've currently given the Hard_Truck, like Econo's GMC Bus and the stock Deathcrusier, and they all behave fine.

Here are some numbers taken from the current .TXT, which works well. I've noted what values give me trouble if I lower or raise them:

Center of Gravity: 0.000000,0.076000,0.550000 (anything less than .55 gives me trouble, including the original .45 I used when I was using a shorter wheelbase and even .50)

Front wheel positions (unchanged):

-0.180,0.1171,-0.346 and 0.180,0.1171,-0.346

Rear wheel positions:

-0.23,0.06,0.98 and 0.23,0.06,0.98

It seems that as I move the rear wheels back, the farthest possible forward point for the CoG to be without the truck bucking moves back as well, i.e. if I changed the rear wheel's front-back position to .88 I could move the CoG up, but that wouldn't be an accurate representation.

I'd be glad if anybody could help me with this. Some of the older members probably recall my fetish for TXT fiddling in past years [img]images/icons/wink.gif[/img]
Boose on Sun Oct 20, 2002 4:25 am
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OMG! Never thought someone would care about it! The model is ages old and back than i had reasons of putting rear wheels position in a wrong place (original), cause i remember having somewhat thesame problems... but not with gravity center. ...oh and suspension vertical moves.

I can't help you now tho, cause i'm all out of carma 2 editing and can't remember shit (might read my own tutorials LOL!), but it's really nice to see ppl fiddle with meh babes =) Good luck on the research, i'd gladly see it fixed.
Kruszchev on Sun Oct 20, 2002 1:01 pm
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jiss, i also use to have these probelem whit the insane kangoro but those come as fast as i have compiled the car, but i doubt that anyone knows how to fixit (or evryone do that exept us, cuz no one ever talk about those errors here.)

Sorry would want to help you but its outside of my "knowlede frames"
User avatar
C2_Scientist on Sun Oct 20, 2002 1:53 pm
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If you send me the .DAT & .TXT files of the truck, I could take a look...
Savage-Elve on Sun Oct 20, 2002 3:13 pm
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Maybe it's because carma gets confused. The gravity center is higher then the rear wheels but lower than the front wheels.What should it do in corners, swing out or hang over ? It can't do both [img]images/icons/tongue.gif[/img]
Secret_Chimp on Sun Oct 20, 2002 6:48 pm
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The number on the far right is the front-back position of the CoG, the number in the middle is the height. It needs to have a high center of gravity, but also one that is front-biased to properly represent the weight loading.

When you have the truck going fast, it has a tendency to get stuck in a light oversteer, but you can get it under control again if you tap the wheels in the opposite direction. When the truck is going slow, it tends to rock to one side when it gets smacked.

There's less traction at higher speeds, not enough traction to cause the truck to tip up. However, the high center of gravity DOES have a negative effect on the high-speed handling (less grip) but doesn't make it tip over. This is the same reason why SUVs have less grip than cars. An SUV weighing the same as a car will generally generate less grip because the weight loading on the tires and suspension during cornering isn't the same.

Besides, C2 doesn't go "this number means swingy tail" or "this number means tippy". It takes all of the numbers and creates a simulation of a vehicle with those handling and geometry attributes.

I think the problem may be that the center reference point of the model (if there is such a thing in C2 model files) is too far forward. If I move stuff too far away from the reference point, C2 gets confused. Instead of the front wheels being .2 away from the ref point and the rears being nearly 1.0, it should be something more like .5 to .7 or .6 to .6. Econo's bus is a good example of this; both the front and the rear wheels are a nearly equal distance away from the reference point.

I'll upload the .DAT and my modified .TXT to my geotitties server soon so people can take a look at it.

[ October 20, 2002: Message edited by: Secret Chimp ]
Secret_Chimp on Sun Oct 20, 2002 11:55 pm
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Here's the .txt and .dat files: www.geocities.com/enigmaticmunkie/truckfiles.zip
User avatar
C2_Scientist on Mon Oct 21, 2002 10:22 am
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All right, here's my suggestion:

First, open the truck in Plaything 2. Select the main model, and then use "modify geometry" (SHIFT+T): Tick the "apply to hierarchy" box, write "-0.39" to Z-axis box, and finally click "apply". Now the centre of the model is in the right place, save the file. Then let's do some modifications to the textfile. Open it, and change these: (copy + paste the parts)

0 , 0.25 , -0.1 // Centre of mass

16 // Mass

0.7 , 1 , 1.88 // Angular momentum proportions

50 // Downforce-to-weight balance speed

4 // Number of 'Wheels' entries.

// Wheel #1

0 // Type

Left front // Identifier

FLWHEEL.ACT // Actor

-0.245 , 0.11 , -0.73 // Position

1 // Steerable flags

0 // Driven flags

0.006 // Suspension give

0.5 // Damping factor

1 // Fractional reduction in friction when slipping

83 , 84 // Friction angles

1.75 // Traction fractional multiplier

0.03 // Rolling resistance

// Wheel #2

0 // Type

Right front // Identifier

FRWHEEL.ACT // Actor

0.245 , 0.11 , -0.73 // Position

1 // Steerable flags

0 // Driven flags

0.006 // Suspension give

0.5 // Damping factor

1 // Fractional reduction in friction when slipping

83 , 84 // Friction angles

1.75 // Traction fractional multiplier

0.03 // Rolling resistance

// Wheel #3

0 // Type

Left rear // Identifier

RLWHEEL.ACT // Actor

-0.325 , 0.11 , 0.74 // Position

0 // Steerable flags

1 // Driven flags

0.006 // Suspension give

0.5 // Damping factor

1 // Fractional reduction in friction when slipping

80 , 83 // Friction angles

1.75 // Traction fractional multiplier

0.03 // Rolling resistance

// Wheel #4

0 // Type

Right rear // Identifier

RRWHEEL.ACT // Actor

0.325 , 0.11 , 0.74 // Position

0 // Steerable flags

1 // Driven flags

0.006 // Suspension give

0.5 // Damping factor

1 // Fractional reduction in friction when slipping

80 , 83 // Friction angles

1.75 // Traction fractional multiplier

0.03 // Rolling resistance

2 // Number of 'Bounding shapes' entries.

polyhedron // Type

8

-0.3 , 0.08 ,-0.93 // L B F

-0.3 , 0.26 ,-0.93 // L T F

-0.35 , 0.26 , 0.92 // L T R

-0.35 , 0.08 , 0.92 // L B R

0.3 , 0.08 ,-0.93 // R B F

0.3 , 0.26 ,-0.93 // R T F

0.35 , 0.26 , 0.92 // R T R

0.35 , 0.08 , 0.92 // R B R

polyhedron // Type

10

-0.3 , 0.08 ,-0.93 // L B F1

-0.3 , 0.77 ,-0.93 // L T F1

-0.3 , 0.97 ,-0.51 // L T F2

-0.35 , 1.0 , 0.07 // L T R

-0.35 , 0.08 , 0.07 // L B R

0.3 , 0.08 ,-0.93 // R B F1

0.3 , 0.77 ,-0.93 // R T F1

0.3 , 0.97 ,-0.51 // R T F2

0.35 , 1.0 , 0.07 // R T R

0.35 , 0.08 , 0.07 // R B R

[DON'T OVERWRITE SUB-PARTS, SHRAPNEL MATERIALS, AND DAMAGE VERTICES!]

CAMERA_POSITIONS

0 , 0.23 ,-0.93 // bumper position

-0.15 , 0.67 ,-0.64 // cockpit position

That's it. Tell me if I missed something.
Secret_Chimp on Mon Oct 21, 2002 1:00 pm
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Uh, yeah, see, I'm on a Mac, otherwise I would have started fiddling with the thing ages ago =P
Savage-Elve on Mon Oct 21, 2002 5:38 pm
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That's what I said, making the y-values for the wheels the same [img]images/icons/tongue.gif[/img]
User avatar
C2_Scientist on Tue Oct 22, 2002 2:15 pm
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Mac? I don't know anything about Mac version... but what's the difference? At least the textfiles you sent were normal...
Buzz on Wed Oct 23, 2002 4:18 am
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plaything doesnt work on macs *they're useless*

[ October 22, 2002: Message edited by: Buzz ]
Secret_Chimp on Wed Oct 23, 2002 1:18 pm
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Um... yeah, ok Buzz....

C2 Scientist, do you think you could upload or send me the modified .DAT file?
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