Data Alignment Issues

turfburn · Joined: 20 Apr 2011 Posts: 11

I sent in a request to the US Support contact, but figure I may get additional points from some of the regulars on here. So minor apology for the two pronged push for information.

I've been trying to do a lot of positional analysis of my autocross runs to see variances in turn in location and braking etc to determine how much they are affecting the run performance. However, the alignment between runs on the data is all over the place for some reason. I am trying to align the graphs based on distance as that should theoretically show if braked sooner or later based on position relative to the corner. However, I have had very little success doing this. I'll try to get screen shots to add to the post to help explain it better, but basically even though the data is aligned that it believes I'm at ".36 km" at a given spot for example, the data is clearly not really at that spot, it shows positions of turns being 100 feet different from one run to another based on the lateral and longitudinal forces and that really isn't possible.

Any ideas/thoughts on what could cause this? It improved a little with the option to correct GPS position data enabled, but it is still ugly. The GPS receiver is on the top of the car completely clear of obstructions so it should be a solid signal, and it usually flashes that it has at least 5 satellites locked, so I'm unsure what could be the issue here - the raw data, or something in the analysis.

Thanks!
Steve

Support · Joined: 31 Oct 2005 Posts: 1343

It sounds like the GPS data just isn't very good - I would suggest that you send a run file to the US office for him to look over. The most common reason is that the GPS antenna is starting to fail.

Regards, Support
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Posted by the Race Technology support team

Rob Stevens · Joined: 31 Oct 2010 Posts: 31

Try enabling the wheel speed option, this should help the speed/distance/gps accuracy, however I've only noticed a slight improvement, also check to see if vibration might be corrupting your acceleration data. I assume autocross is like our sprinting, one car at a time not on a circuit, a sprint?

turfburn · Joined: 20 Apr 2011 Posts: 11

osborni · Joined: 07 Dec 2007 Posts: 473 Location: USA, Michigan

I had an antenna fail with no visible damage to the wire....
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BMW 2000 M Coupe

turfburn · Joined: 20 Apr 2011 Posts: 11

turfburn · Joined: 20 Apr 2011 Posts: 11

I pulled up some data, I need to dig through more, but I'm seeing positional accuracy values provided between 2.52 and 3.4 on average with a spike here and there to 4 or 5. I'm assuming the units are meters. Not sure if that is good/bad or average.

Thanks!

jlucas · Joined: 29 Nov 2005 Posts: 304 Location: Delaware, OH

That sounds like normal averages to me.
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Jeremy Lucas
Fast Tech Limited - a Race Technology Dealer

turfburn · Joined: 20 Apr 2011 Posts: 11

jlucas · Joined: 29 Nov 2005 Posts: 304 Location: Delaware, OH

I'm not sure this right term but I think of that as an absolute GPS accuracy, the run to run accuracy is greater than that.

I don't have personal autox experience with a DL1 so I can't be much further help, but you can move the data in the run manager so that your start & end points line up between runs to account for any GPS drift (same goes with road race stuff).

You cannot get steering angle off of OBD2. You need either the manufacturer CAN code (and CAN adapter) or a dedicated sensor.
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Jeremy Lucas
Fast Tech Limited - a Race Technology Dealer

turfburn · Joined: 20 Apr 2011 Posts: 11