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Forces on a skidding car ?

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Hello. I have another car game physics question. If a car is skidding how does the wheels act on a car. Does it matter if you brake or give some gas ? And does it matter how the wheels are turned, or does the car just skidd in the direction that the inertia wants it to ? I have thougt of one way to calculate the driving force from the driving wheels. That is to take the force that the wheels are giving and multiply it with the dynamic koeficient of the two materials that is involved ie. 0.75. Is this a correct way ? Any comments on this subject will be appreciated =) /Niklas

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If you haven''t already had a look here, I suggest you do. The page has pretty much all the theory you''ll need to do car physics.

http://home.planet.nl/~monstrous/tutcar.html

But anyway, if the car is skidding, the wheels are still applying friction. If the wheels aren''t pointed the same way as the car is moving, they''ll create more friction and slow the car more, because they can''t roll properly. I''d expect brakes to help somewhat. Giving it the gas could spin the car around or whatever...

If you want a semi-realistic semi-arcade physics system, playing Carmageddon would give you some insight on how things work.

Multiplying the force the wheels put down by a surfaces "grip" coefficient is a very good idea - it''d let you make the car slip around and such when you go from the road to grass...

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quote:


I have thougt of one way to calculate the driving force from the driving wheels. That is to take the force that the wheels are giving and multiply it with the dynamic koeficient of the two materials that is involved ie. 0.75. Is this a correct way ?




Not really. That way means there is a massive constant loss of energy from the wheel transmitting the force, hence the wheel will be like constantly skidding. A drive train as an efficiency factor, but a loss of more than 25% is a bit extreme

The force transmitted by the wheel is the force transmitted by the engine (more like the torque over the radius of the wheel), capped to the maximum force a tire can take.

I'm generalising, but for a non turning car, A maximum driving force a tire can take is

|Fd| = grip * |Fn|

where Fn is the vertical force on the tire, and Fd the driving force. the grip value is the grip of the tire, which is influenced by the combined coefficient of friction of the rubber and the surface. Drive on grass, and the grip will decrease dramatically. Therefore, the maximum driving force will decrease, which would make the car less easy to stop and more prone to skid. The grip depends also on the tire temperature, the pressure, the size of the contact patch, ect... Also, a tire just don't loose grip that abruptly. It's usually a smooth curve, so you don;t loose control straight away. That curve can be controlled by the tyre pressure, vertical load, type of rubber, which would make the tire behave differently depending on those factors.

see this

http://members.xoom.virgilio.it/adiaforo/epcjk.htm


[edited by - oliii on August 5, 2003 8:43:49 PM]

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