Vehicle suspension characterization

[Navion]

Hi,

I have a motor home that rocks quite a bit when entering driveways, speed bumps, etc. I've added some mods like Koni shocks & struts, rear http://www.timbren.com/" rubber springs, but was never able to quantify the improvements. Well times have changed! I got a hold of a M52223 processor demo board (with 8 12-bit adc) and purchased a MMA7260 accelerometer to take suspension measurements.

I got it setup so that the processor measures the x (side to side), y (front to back) and z (up/down) axis voltages every 5 ms. The accelerometer scale factor is 800 mV/g.

My latest project was to add a larger rear sway bar (SB). The old one is 33 mm and new is 36.5 mm diameter.

I ran several tests. I first pushed against the side of the motor home to get it rocking. The data showed little difference between the two SB. Should the SB help against side rocking?

My second test is to go over a speed bump at an angle. Though there are differences, they don't seem dramatic.

Old SB

New SB

The time axis in the graphs is in units of 5ms. The mark "200" = 1 second
The second graph is a FFT of the data.

Over all there isn't as much improvement as I expected. The shock damping also doesn't look that great.

Here's my main question. Given the data, how does one determine the damping coefficient?

Do you guys see anything special in these graphs? Peak to peak side movement of one g-force seems fairly high, doesn't it? Dishes fly out of the cabinet if not locked!

Thanks for helping me understand the data.

Navion

 

[eljose79]

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Hi Navion,

Thank you for sharing your project and data with us. It is great to see individuals taking a scientific approach to improving their motor home's suspension.

Based on your data and observations, it seems that the larger rear sway bar did not have a significant impact on reducing side-to-side rocking. This could be due to several factors, such as the stiffness of the rear suspension or the positioning of the sway bar. It may be helpful to compare your data to other motor homes with similar modifications to see if there are any noticeable differences.

To determine the damping coefficient, you will need to measure the force and velocity of the suspension as it responds to a disturbance. This can be done using specialized equipment or by analyzing the data from your accelerometer. The damping coefficient can then be calculated using the formula: damping coefficient = force/velocity. This value will give you an idea of how well your shocks are dampening the suspension movement.

In terms of the peak-to-peak side movement of one g-force, it does seem quite high. This could be due to a combination of factors, such as the weight distribution of your motor home, the stiffness of the suspension, and the quality of the shocks. It may be worth considering additional modifications or upgrades to help reduce this movement.

Overall, your project is a great example of using scientific methods to improve the performance of your motor home's suspension. Keep collecting data and experimenting with different modifications to find the best solution for your needs. Good luck!