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      02-17-2011, 12:08 AM   #63
Kind of a Big Deal

Drives: an 1M not often enough
Join Date: Jan 2011
Location: between Unlimited and Hard to Get

iTrader: (0)

Originally Posted by JAJ View Post
Getting the "clean" signal wasn't easy - it's very prone to small offset errors and to noise, so a full second of sensible results takes an hour or so to process by hand.
Is the process by hand the elimination of errors or more? Did your integration involve some smoothing or data(n+1) = data(n) + d data(n) / dt * delta t?

Originally Posted by JAJ View Post
The run out of travel events are the flattening of the top of the suspension compression curve. I didn't go over the speed bump very quickly and it only just touches, so the "impact" is only really visible in the processed output - in the raw data it's buried in the noise and rumble. I don't recall a "thump", but then it was a year ago.
Looking at it more closely, I see what you mean now: the top of the wheel/suspension curve is flatter than expected from a harmonic signal. From the technical drawings I recon that bump stops nowadays have their own additional spring and damping characteristics, rather then being hard stops but I still would expect a more significant deviation (acceleration spike) from the harmonic line. It could also be related to the shape of the bump (~flat top?) and/or a dry friction effect? Once I have time I wouldn't mind looking into deriving the shocks damping coefficient [Ns/m] and dry friction force from your curves. The mass (or weight), front-rear balance and spring rate of the measured setup would be useful for that (and if willing to share, the measurement data). My goal here is mainly to get a feel for the damping coefficients used in M3 shocks and in the end to quantify the difference in EDC damping settings vs their drive signal.

I started diving into old Matlab stuff and found that it lets you record directly from the PC's line-in, but I would need an accelerometer with the right output signal. Did you consider accelerometers with analog output?