Estimate Damping Coefficient of Car with Hand Bouncing & Dropping

In summary, the conversation discusses the possibility of estimating the damping coefficient of a car by hand bouncing the car and observing its harmonic motion. The possibility of using other techniques, such as dropping the car, is also mentioned. It is suggested that with some math, a relationship between the damping coefficient and the time it takes for the car to reach a certain fraction of its initial amplitude can be derived and tested. However, the complexity of car dampers, which are not symmetrically damped, may make it difficult to accurately estimate the damping coefficient. The role of damping in preventing the wheel from overshooting and causing oscillation is also mentioned.
  • #1
zacharoni16
19
0
I was wondering how I can estimate the damping coefficient of my car by doing the hand bouncing the car body and watching the motion of the car?

Mechanics usually bounce the car by applying hand force and watching how the car moves in harmonic motion. Is there a way to estimate the damping coefficient by using this technique?

Or is there another technique like dropping the car a few inches or something to estimate it?
 
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  • #2
The motion of the car is of course (intentionally) overdamped, to keep you from bouncing around forever. How fast it returns to equilibrium depends on the damping coefficient quite directly. So with a bit of math, you could derive a relationship between the damping coefficient and the time it takes, for example, for the amplitude to reach some fraction of the initial amplitude. Then you could easily test this by bouncing the car by hand and measuring this time. Then you can just plug in the time and calculate the damping coefficient. Note that in the theoretical calculation, the damping is exponential so it will never quite reach zero. However, the car quite obviously stops bouncing after two or three periods. This introduces a bit of uncertainty in when you decide which fraction you will take. I guess something like 1% could do, in physics 1/e is a common factor.
 
  • #3
Car dampers are not symmetrically damped. There is purposely less damping on compression (to allow the wheel to ride sharp bumps and to give a softer ride) than on recovery. The have a flap valve inside which closes some of the holes in the piston on the down stroke.
This makes the 'damping coefficient' a bit less accessible than for a simple damped oscillator.

@CompuChip
The damping has another function. It stops the wheel overshooting when it is thrown upwards by a bump. The wheel-spring combination has a much shorter time constant than the car-spring combination and it is easy to get a resonance with the wheel and tyre. You can get an oscillation, particularly when braking and the wheel can actually leave the road in a series of bounces. It also plays hell with cornering as your traction can be halved. I had a Renault 4 that did this until I replaced one of the rear dampers. Very dramatic but no noticeable affect on the 'ride' as the torsion bar suspension was very soggy anyway.
 
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What is damping coefficient?

The damping coefficient is a measure of the resistance to motion of a car's suspension system. It is a numerical value that represents the amount of energy that is dissipated as the car's suspension compresses and rebounds.

Why is it important to estimate the damping coefficient of a car?

Estimating the damping coefficient of a car is important because it allows us to understand how the car's suspension system responds to different road conditions and how it affects the car's handling and stability. It also helps us to identify any potential issues with the car's suspension.

How can the damping coefficient be estimated with hand bouncing?

To estimate the damping coefficient of a car using hand bouncing, we can simply push down on the car's bumper or body and observe how quickly it returns to its original position. The faster it returns, the higher the damping coefficient. This method is often used as a quick and simple way to get a rough estimate of the damping coefficient.

What about dropping the car by hand?

Dropping the car by hand can also be used to estimate the damping coefficient. By lifting the car a few inches off the ground and dropping it, we can observe how many times it bounces before coming to a rest. A higher number of bounces indicates a higher damping coefficient, as more energy is being dissipated with each bounce.

Are there any other methods for estimating the damping coefficient?

Yes, there are more sophisticated methods for estimating the damping coefficient, such as using data from sensors and performing calculations. These methods can provide more precise and accurate results, but they require specialized equipment and expertise.

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