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GPS / OBD / etc datalogging thread. How and why + discussion


Roman

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Hey people,

 

Thought I'd start a fairly broad topic tech thread, about various types of datalogging.

 

So including things like:

 

GPS lap timing

Aftermarket ECU datalogging

OBD port datalogging
Using video as a follow up tool!

And so on.

Will post some jibba jabba in the following posts, feel free to contribute if you've got anything interesting relating to engine or car datalogging.

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I just went to my first trackday where I had my GPS setup working.

This uses a netbook PC, a 20hz USB GPS reciever, and a program called Racechrono that you can download for free on PC/tablet/etc:

http://racechrono.com/

So basically, when I was out on the track I could use this setup to show me split times and laptimes in real time.
If I just completed a segment of the track quicker than last time, the laptop screen would flash green.
If I just went slower, it would flash red.
So super useful to help figure out what's actually faster or slower at particular parts of the track.
In the program you can set your own 'traps' to mark out your split times to suit what you're trying to measure or acheive. Which is awesome.

 

This worked well through the day, however there were some parts of the track where I'm still not sure which type of line is fastest.
Since I had all of the laptimes logged, once I found some time I had a sift through the GPS data and find out what actually works best.
On the Taupo full track I had my suspicions that a wider line through the start of the sweeper was better, and seemed to give a better line through the second half and onto the straight.

 

But looking through a comparison of two lines, you can see this is not the case at all, red car vs blue car:

 

upbnpyoy.miq.jpg

Taking a tighter line meant I gained a bunch of meters which equated to about half a second difference by the time I reached the end of the straight. It's pretty cool to have information like this on hand! Based on some information I've gained from the GPS data, I've written myself a few notes about how to take a few of the corners differently for next time, and try knock some time off.

If anyone wanted a quick and easy way to setup racechrono if going to a trackday, you can download it onto a tablet or android phone and just use the internal phone GPS to record the laptimes. It wont be as accurate this way, as generally internal GPS recievers in phones and tablets which are designed for navigation only run at 1hz. So if you're going 150kph, you're travelling about 40 meters in between each point that the GPS receiver reads.

So having a higher sampling rate for the GPS is ideal, as well as a strong reciever that can pick up a lot of satellites to average the signal from.
Most 'out of the box' GPS datalogging units designed for racing etc work at 10hz or there abouts. However, any information is good information.
A 1hz GPS setup is still leagues ahead of what anyone had even 20 years ago, and you can use it for free with stuff you already own. Amazing!

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I built a very basic excel table which allows you to track actual speed and position on an overlay of the track based on the .CSV extract from racechrono, quite handy to look at max cornering speeds, you scroll thourgh with the bars to zoom in the speed plot..

 

teretonga_zps313ff3c0.jpg

 

 

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oh cool! Something handy as well is to download 'circuit tools' which is another free download, and then export from racechrono as the. vbs format (i think) to load in the program.

You can compare up to six laps at once in that program, instead of just two in RC.

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