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Hey guys, have any of you used/heard of the programs to use mobile phone GPS to do lap timing such as:
http://www.racechrono.com/
or
http://www.gpslaptiming.com/page.php?id=5&lang=eng?

They can be used with a GPS phone like the Nokia 6110 Navigator or other mobiles with a bluetooth GPS receiver and they're free! I've seen good reviews at other sites and was thinking of giving it a go some time.

Certainly cheaper than a Performance Box etc.

I have played with racechrono, seems to go OK, but most of the bluetooth GPS units have a 1Hz refresh rate and so the accuracy of the lap time is +/-0.5 sec (I think). Performance box is a faster update (10 Hz?) so is more accurate. For practice lap timing racechrono is not bad, accuracy for max / min speeds seems fairly low. If you already have a gps reciever then the price (free) is great.

Well I have a K800i but I was thinking of getting a 5Hz receiver.

Even with a 1Hz receiver the accuracy should be significantly better than +/-0.5 s because I'd imagine that it interpolates between data points using both velocity and acceleration.

For most purposes +/-0.1s accuracy would be fine and 5Hz should achieve that I reckon.

Anyway I'll try to convince a mate to swap phones for a weekend to see how it goes and if it works well enough I might buy a receiver for my own phone.

FWIW, I'd still love a Performance Box though.

tinsfci wrote:I have played with racechrono, seems to go OK, but most of the bluetooth GPS units have a 1Hz refresh rate and so the accuracy of the lap time is +/-0.5 sec (I think). Performance box is a faster update (10 Hz?) so is more accurate. For practice lap timing racechrono is not bad, accuracy for max / min speeds seems fairly low. If you already have a gps reciever then the price (free) is great.

its not really free

i installed the first one and it expires sometime in June

the 2nd one is a demo haven't install it yet tho

I'm having a muck around with
http://www.gpslaptiming.com/page.php?id=5&lang=eng

Picked this one because it would work on my current phone. The demo appears to work OK so I have ordered to full version for $17, I'll let you know how it goes.

Bruce

fattima wrote:I'm having a muck around with
http://www.gpslaptiming.com/page.php?id=5&lang=eng

Picked this one because it would work on my current phone. The demo appears to work OK so I have ordered to full version for $17, I'll let you know how it goes.

Bruce

Just bumping up an old thread here, how did it go?

I've now installed Racechrono, but won't have a chance to test it out until this weekend.
Anyone have some feedback on it?

I'll try to borrow a GPS phone for Phillip Island in mid December. We'll see how it goes. I'm fuming that I didn't bid more on a Driftbox that came up on eBay though!

Racechrono is actually free. It only expires so the author can ensure PPL move onto newer versions. I grabbed a 5Hz Bluetooth GPS unit for about $50 via ebay and ran it with my N95 at Lakeside. In fact I plotted the track that you can download from the Racechrono site. Timer was pretty accurate when compared with a stopwatch (finger lag aside) and others' in car footage.

For a freeby, its pretty good.

Fra66L wrote:I grabbed a 5Hz Bluetooth GPS unit for about $50 via ebay and ran it with my N95 at Lakeside. In fact I plotted the track that you can download from the Racechrono site.

Did you try it with the built in GPS on the N95 first?

Yes, and it did work, just wasn't too accurate.

thanks, I guess I'll see how it goes and if needed get an external GPS module later on

Due to my car having no engine I've been using it on the pushie with a Nokia e51 and a QStarz BT-Q818eXtreme 5Hz external unit. It's brilliant - gives me times over saved point-to-point routes or circuits with stage times and speeds over the entire ride in a nice graphical display on the Nokia. Seems accurate to about 1 metre. Takes a while to figure it out, then all good.
I also used it on a Nokia 6120 but that phone doesn't have the cpu speedto run it properly.

Apparently, you can also use the Racechrono data files with the Performance Box software. That gives you the best of both worlds. The only part you miss out on is the live display of laptimes (presumably Racechrono doesn't do this???).

Interesting comments about interpolation of laptiming. My 10Hz Performance Box only reports lap times to the nearest 0.1s ie. it does not interpolate. The figures on the racechrono site don't make sense to me: 1Hz (1s between samples) gives +-0.25s, 5Hz (0.2s between samples) gives +-0.15s. I'd think that the best they could do would be +-0.5s at 1Hz and +-0.1s at 5Hz (ie half the sampling interval). Perhaps both of them have been calibrated against a higher precision timing method and therefore factor in the inaccuracy of position locating???

Guran, I reckon you've probably answered your own question because the precision would be limited by the sampling frequency and the positional accuracy. The accuracy would vary with speed too, because the position error would be a smaller percentage at higher speed so those numbers would only be generalisations.

Also, doesn't the PerformanceBox have the option of 1/100 s precision? Screen captures at the Racelogic website show laptimes stored to 1/100 s but the live timer only displaying 1/10 s precision.

Damn I wish one of these would fall into my lap!

Damo wrote:Guran, I reckon you've probably answered your own question because the precision would be limited by the sampling frequency and the positional accuracy. The accuracy would vary with speed too, because the position error would be a smaller percentage at higher speed so those numbers would only be generalisations.

Thanks Damo. I thought it must have been something like this.

Also, doesn't the PerformanceBox have the option of 1/100 s precision? Screen captures at the Racelogic website show laptimes stored to 1/100 s but the live timer only displaying 1/10 s precision.

Not that I've noticed. The software has been updated though, and perhaps there's an option to extrapolate to 1/100s. I'll check. The Vbox and similar units log at 100Hz, so they do report to 1/100s. But they cost a hell of a lot more!

Damn I wish one of these would fall into my lap!

It's a cool toy alright. Have you earmarked your Kruddy payment yet?