affordable lap timer

cossie1600

What hertz can the OBDII logger log at? My datalogger logs at 10ghz while the obdII reader logs at random rates, makes it impossible to provide a consistent set of data.

Damn the external GPS are pretty pricey if you want 10ghz

wstar

On the GPS: The 818XT is switchable between 10Hz mode (with GPS only, no differential), and a programmable 1-5Hz mode that uses differential GPS (more accurate). From the forums for various lap timer software on android, it seems like the 5Hz D-GPS mode is actually better (more accurate, faster fixes, and still you're getting 5 position updates per second, which the software can extrapolate movement curves between).

OBD-II loggers vary a lot, it's kind of a murky area. With the PLX Kiwi and my phone, I get somewhere around 4Hz update rate most of the time. So for instance it will rarely catch the exact peak RPM just before a shift, but it's "close enough" for data analysis. Software like aLapRecorder logs all the inputs (phone G-sensors, OBD-II data feed, GPS data feed) and then reformats it into a combined data output file for rendering software (e.g. a single CSV file for RaceRender), which in turn probably does a little of its own smoothing and/or interpolation.

It doesn't really matter if OBD-II and GPS data line up at the same update frequency rate or not, or shouldn't with quality software on the other end interpolating them as approximating smooth value curves.

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wstar

On the expensive front, the ultimate thing seems to be ChaseCam. If you buy all the right options from them, you can have 1-4 cameras, accurate GPS + G-force, OBD-II, as well various other external sensors (independent RPM pickup, and a whole lot more), and it all logs in sync to a memory card. The problem is price. I just can't justify the 2-3K+ even for a basic setup that does a better job than my hackish Android stuff (which works "good enough" for amateur-level playing around anyways).

e.g. check out this sample video, where it's even logging all kinds of suspension/wheel-based data:

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7AT Track Car!
Journal thread / Car setup details