the ultimate car physics Problem.

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quickquestion
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the ultimate car physics Problem.

Postby quickquestion » Sat Apr 15, 2017 11:22 pm UTC

Ok so I do not think they teach the answer to this in highschool or even college physics. But I am trying to make car physics for a game, so the problem is this.
What ratio of force does each tire apply to the car?
http://pasteboard.co/4LbI40eKd.png

Also, assume the static friction coefficient of the Tire is set to 1000 or some very high value.

Basically, the idea is, a standalone simulated rubber tire should have a lateral force applied to it in the opposite direction of lateral motion. Solving this for 1 single tire easy: The amount of lateral force should = tiremass*lateralvelocity.
However, this becomes much more complicated when 4 tires are attached to a body. So I am not sure what the answer to this problem is, but if someone solves this, I will probably be able to judge whether they are right and correct.

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Re: the ultimate car physics Problem.

Postby doogly » Sun Apr 16, 2017 6:21 pm UTC

quickquestion wrote: So I am not sure what the answer to this problem is, but if someone solves this, I will probably be able to judge whether they are right and correct.

That is a dangerous way to think.
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Re: the ultimate car physics Problem.

Postby morriswalters » Sun Apr 16, 2017 7:02 pm UTC

I thought there was a 5 post requirement for links?

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Re: the ultimate car physics Problem.

Postby somitomi » Sun Apr 16, 2017 10:24 pm UTC

I'm not sure about what the scenario is based on that drawing:
1) Car is moving, wheels are locked up (not rotating): the orientation of the wheels is irrelevant, using the equation Flat=Fvertkin is good enough to my knowledge. The downward force on each wheel depends on acceleration and such, but depending on how much detail the game has (how detailed your suspension model is), assuming some static load distribution between the wheels could work. I assume this isn't what you're asking, because this is relatively uncomplicated (unless you account for the dynamic forces on the wheels).
2) Car is moving, wheels are roating: is a lot of headache, because the direction and magnitude fo the force depends on both the side-slip and longitudinal slip. There are multiple mathematical models describing this because noone is exactly sure how it works, and sadly my knowledge doesn't extend beyond this at the moment. I could try to look it up, but I can't promise anything...
3) Car is not moving, wheels are rotating: (assuming the drivetrain to be simpler than it actually is) you can probably get away with using dynamic friction.
4) Car is not moving, wheels are not rotating: usually means no lateral force, but in case there is (car is standing on an inclined plane or there's wind or something) the equation for static friction should work here.
I'm kind of puzzled why the wheels are pointing all sorts of directions by the way
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Re: the ultimate car physics Problem.

Postby morriswalters » Mon Apr 17, 2017 1:24 am UTC

What am I missing? It's like it almost makes sense. But only almost.

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Re: the ultimate car physics Problem.

Postby moiraemachy » Mon Apr 17, 2017 11:22 pm UTC

Yeah, as somitomi said, this is complicated to properly model. But in the case of simulated physics in a game, maaaybe you can get away by using 3 different friction coefficients: one for side slip, one for longitudinal slip (when braking), and one for regular longitudinal (when not braking). Then you simply decompose the velocity vector in side slip and longitudinal components, and calculate the forces separately.

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Re: the ultimate car physics Problem.

Postby morriswalters » Tue Apr 18, 2017 2:20 am UTC

moiraemachy wrote:Yeah, as somitomi said, this is complicated to properly model. But in the case of simulated physics in a game, maaaybe you can get away by using 3 different friction coefficients: one for side slip, one for longitudinal slip (when braking), and one for regular longitudinal (when not braking). Then you simply decompose the velocity vector in side slip and longitudinal components, and calculate the forces separately.
You don't seem to have enough relevant information to say much of anything useful. He gives you a velocity and a weight, but no center of gravity, no wheel height, no temperature, no description of the road. Or the weather. No center of gravity is the real show stopper isn't it? What if your driving a double decker London bus?

And I know I'm not the brightess bulb here, but cars are designed to never let the wheels get set that way. Why would you attempt to model it?

He suggested a coefficient of friction of 1000, rubber on asphalt is about .9. Why that high?

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Re: the ultimate car physics Problem.

Postby somitomi » Fri Apr 21, 2017 1:58 pm UTC

morriswalters wrote:You don't seem to have enough relevant information to say much of anything useful. He gives you a velocity and a weight, but no center of gravity, no wheel height, no temperature, no description of the road. Or the weather. No center of gravity is the real show stopper isn't it? What if your driving a double decker London bus?

And I know I'm not the brightess bulb here, but cars are designed to never let the wheels get set that way. Why would you attempt to model it?

He suggested a coefficient of friction of 1000, rubber on asphalt is about .9. Why that high?

The drawing doesn't have the necessary info, but the game itself probably has some of them. Besides, unless we're trying to make a rigorous simulation to work out the code for an ESP-module in a new double-decker bus, we can probably ignore some of the less significant factors like temperature. But yeah, we need a little more information on what should be achieved and what to start with.
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Re: the ultimate car physics Problem.

Postby morriswalters » Fri Apr 21, 2017 2:58 pm UTC

I thought when I posted it was some kind of a joke. I still do. I was trying to be circumspect and not say it directly. If I just unfairly demeaned the OP I will apologize when I understand exactly what he was trying to accomplish with that drawing.


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