# Spring-Damper

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Heya to all, i read more than one time here that a good start for a car came is to make the spring-damper works... i searched a lot a good paper explaining how this work but i wasn't able to find any decent (wich had something near to do with cars almost). Can anyone of you point me out to a right place? thank you

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Hmmm. One good place to look is at college textbooks on the mechanics of vibrations, for example "Mechanical Vibrations" by Rao.

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But, to give a *very* brief overview, a spring-damper system is one in which a spring and a damper both connect two points together. For a car, you'd have a spring and damper between the wheel and body of the car.

The spring causes a force that is approximated by Hooke's Law:

Spring Force = -kx

where k is the spring stiffness (units are force/length) and x is the change in length of the spring from its equilibrium/no-force length. The negative sign refers to the fact that if the spring is stretched to be longer (x is positive), the force acts opposite the stretch to return the spring towards its equilibrium length. If the spring is compressed (x is negative), the force acts opposite the compression, again to return the spring towards its equilibrium length. Note that the spring force acts on both objects that the spring is connected to, in opposite directions. For a stretched spring, the force on each end, magnitude kx, acts back towards the center of the spring. For a compressed spring, the force on each end, magnitude kx, acts away from the center of the spring.

Now, a spring alone, connected to bodies with mass, will cause high oscillation for a long time in real-life. A damper causes the system to return to equilibrium more quickly with oscillations that go away faster. In numerical simulation, springs cause numerical havoc, and can cause simulations to blow up (numerical overflow or general chaos). A simulated damper can help stabilize the simulation.

The way a damper works is this:

Damper Force = -cv

where c is the damping factor and v is the velocity component of the object parallel to the damper and measured relative to the other end of the damper and . For example, if the damper is connected to objects O1 and O2, with velocities V1 and V2 (measured in world space), and the direction of the damper is D, the damping forces applied are:

Damping Force on O1 = -c((V1 - V2) dot D)
Damping Force on O2 = -c((V2 - V1) dot D)

(dot means dot product)

Hope that helps.

thank you!

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