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      06-22-2012, 11:46 PM   #77
BigMacSmallFries
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Drives: '15 M3, '11 GT3 RS
Join Date: Aug 2010
Location: Toronto, Ontario

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Dude, I'm impressed. Thanks for putting this altogether, and for the others pitching in. Glad I have a working knowledge of our suspension set up.

So, what I'm gathering for those keeping their cars on the street and wanting to keep the costs low is that the Dinan springs with the shortened bump stops are the only way to go (from the lowering spring choices). Track use really requires stepping up to the Coilovers.

..I imagine for those of us tracking only a few times per year, the Dinan would be acceptable for the occasion. Any comments?





Quote:
Originally Posted by JAJ View Post
Essentially, I couldn't find a string of data points (in an hour or more of data) that would behave sensibly for more than a second or so. You're double integrating, so the process is to integrate from acceleration to velocity, detrend it, then integrate velocity to position and detrend it again. If you pick your start and end points when you can be confident that the suspension is at static height, then you can look at movements away from that static height. You can also look at motion from a "sensibility" perspective to see whether the data says the suspension is in places that physically it just can't go.

For sets longer than a second, you don't get consistent trends for detrending. The accelerometer signal has (what I presume is) low frequency noise components that make the integrated result wander around by 10's of cm over a few seconds.



I did a force vs velocity curve for the OEM dampers based on the acceleration data. F=MA, sprung and unsprung masses and known spring rates allow you to compute the forces and velocities of the suspension parts and graph the contribution from the dampers. This is actually easier to do because you only integrate once, and you can get enough samples to see the shape through the noise. It was an interesting exercise, but I can't find the data on my laptop, and I may have chucked it in a fit of cleaning up.

I thought a lot about analog accelerometers because I'm an analog circuits guy from decades ago. That would have been vastly easier for me to set up and calibrate than digital processing, but vastly harder to post process. I'd have been able to bandpass filter it, integrate and detrend it and get meaningful numbers without breaking a sweat. Digitally, it's not so easy for me. If I was starting now, though, I'd take a close look at Bosch BMA180 digital accelerometers - they have built-in bandpass filtering and data cleanup. They might work better.