Estimating spring coeff and damping coeffient of my car


by zacharoni16
Tags: coeff, coeffient, damping, estimating, spring
zacharoni16
zacharoni16 is offline
#1
Jan8-13, 09:18 AM
P: 19
I'm working on a project, I just need ballpark estimates for the spring constant and damping coefficient for my 1994 Nissan Pathfinder SUV.

I was thinking of using Hookes law to estimate the spring constant, can I just measure the ride height of the car with nothing in it, then add 200 pounds of weights in the back and measure the displacement from the reference to get the spring constant?

For the damping, I know most cars are near critical damped right? to make oscillations die out fastest.

I'm using the quarter-car model for my project and I just need to estimate these two parameters on a real car


Any advice or suggestions would be awesome. I know damping they used to do a drop test and watch the oscillation for a "shock" test but I dont have the tools or a jack to safely do this
Phys.Org News Partner Physics news on Phys.org
Information storage for the next generation of plastic computers
Scientists capture ultrafast snapshots of light-driven superconductivity
Progress in the fight against quantum dissipation
AlephZero
AlephZero is offline
#2
Jan8-13, 02:23 PM
Engineering
Sci Advisor
HW Helper
Thanks
P: 6,341
Quote Quote by zacharoni16 View Post
I was thinking of using Hookes law to estimate the spring constant, can I just measure the ride height of the car with nothing in it, then add 200 pounds of weights in the back and measure the displacement from the reference to get the spring constant?
That's a good idea, but I would forget about the 200 pounds weight. Jack up the car, and see how far you have to raise the car body before a tire lifts off the ground. That way, you will be using the weight of the car "for free".
I know damping they used to do a drop test and watch the oscillation for a "shock" test but I dont have the tools or a jack to safely do this
You can get a rough idea by just "bouncing" the suspension by hand, and counting how many half-cycles the body moves before it stops. The oscillations will be fairly slow, so you could video them with a cellphone or digital camera and then measure the images frame by frame to get a graph of the displacement agaisnt time. Then try to make your spring-mass-damper model match what you measured.
zacharoni16
zacharoni16 is offline
#3
Jan9-13, 01:21 PM
P: 19
So you mark a reference point, jack the car up until the tire barely lifts off the ground, that distance from the reference is the displacement, and I use the car weight as the force as listed in the owners manual? Or would I use 1/4 of the weight since its one tire?

AlephZero
AlephZero is offline
#4
Jan9-13, 01:30 PM
Engineering
Sci Advisor
HW Helper
Thanks
P: 6,341

Estimating spring coeff and damping coeffient of my car


Quote Quote by zacharoni16 View Post
Or would I use 1/4 of the weight since its one tire?
Correct. The weight might not be split 50/50 between the front and rear wheels, but if you don't know the CG position of the car that's a reasonable assumption.
zacharoni16
zacharoni16 is offline
#5
Jan9-13, 02:30 PM
P: 19
Thank you!

For the damping, the half-cycles would be the peak to peak every time it comes "up" correct?

If I video tape it I will just need to know the FPS of the camera to get a time scale like they do on myth busters?
zacharoni16
zacharoni16 is offline
#6
Jan10-13, 07:01 PM
P: 19
Confused :/ any help thank you AlephZero
zacharoni16
zacharoni16 is offline
#7
Jan11-13, 11:55 AM
P: 19
If I count every time the car goes above the ride height that is a half sine (half of a cycle) ??
zacharoni16
zacharoni16 is offline
#8
Jan13-13, 06:13 PM
P: 19
bump


Register to reply

Related Discussions
Bump detection using accelerometer inside car, estimating suspension damping Introductory Physics Homework 15
Gas Strut - Damping coeff and spring constant Mechanical Engineering 4
Estimating the damping coefficient of a wave assuming a very small ratio Advanced Physics Homework 1
what is the relationship between mass absorption coeff. and linear absorp. coeff.? General Physics 1
stretched spring --find coeff of friction Introductory Physics Homework 13