GPS based Lap Timers

[RickyBobby]

Originally Posted by jml

Here is what I am talking about, notice on the G2X (below) that the data is VERY much aligned. (All data from TWS in my E90)


On the traqmate (below), similar data, but out of alignment between laps (sat vs sunday). This is caused by drift, and was explained to me to be something that is "sometimes" normal by the tech support at traqmate. We tried different GPS loctions, different receivers, different main units. Same results. Pretty frustrating when you are used to the accuracy of the G2X unit, which was flawless IMO, except for the usability of the software.

The traqmate software has functionality to fix the sat drift. Did you ever try that? Seems like a shame if that's the only reason you got rid of yours.
I've only had my traqmate for one weekend so I don't have enough data yet to see any drift. Time will tell.

[lucid]

Originally Posted by RickyBobby

The traqmate software has functionality to fix the sat drift. Did you ever try that? Seems like a shame if that's the only reason you got rid of yours.
I've only had my traqmate for one weekend so I don't have enough data yet to see any drift. Time will tell.

Thanks for the info. If you have more track time within the next 2-3 weeks (my purchasing timeframe), please let us know if the drift issue is resolved.

Edit: Are you happy with the video integration (if you have video)?

[MaxL]

Originally Posted by cchan

The iPhone only samples GPS locations about 1x per second and the built-in antenna isn't the most accurate, so be aware of those limitations. Apps like Harry's give a good taste of data acquisition though, especially for the price. I have a G2X system, but if I was going the lowest cost route, that would be the one I would use.

There is a way to use external bluetooth GPS with 5Hz or even 10Hz update rate (real, not interpolated) on iPhone. My GPS datalogger has an option of working as an external blutooth GPS, so I am going to try it with the Harry's app for recording G-forces and overlaying lap map on the video (something my datalogger cannot do by itself). Will report back in April.

[dogbone]

Regarding external GPS sensors for iPhone, I bought the Emprum UltiMate GPS hardware device that attaches to the iPhone to work with Harry's Lap Timer Pro and it is very accurate. It has 5Hz refresh (5 times/second) and is usually tracking 9-11 satellites when on the track. It supports Differential GPS which means it not only tracks satellites in the sky, but also ground based stations which really increase the accuracy.

I just leave it inside the center console of my E90 M3 with the lid shut and it's fine in there. I have a GoPro and record all my laps and go back later and time them watching the video, and Harry's Lap Timer Pro and the Emprum are always spot on.

I have a friend in the aero-space industry who is working on the new GPS-based air traffic control system (ADSB), and I was asking him how much I could trust a device like an Emprum. He said when the device is in Differential GPS mode, that it's extremely accurate.

hehe a side note in all of this: Harry's Lap Timer and the Emprum work as a speed checker while driving down the road. My analog speedo is 6mph off, and my digital speed readout is 4mph off.....so if it shows 70mph on the iPhone screen, the digital display on the car shows I'm going 74 and the analog dial shows 76.....

[M3 Montreal]

I also use Harrys Lap Timer with a TomTom cradle which was recommneded by the makers of the program. The cradle has a built in antenna to boost accuracy and it works great.

[dnvrdrvr]

Another option that I'm considering is Race Keeper. Went to an all-day data workshop last month and was impressed with what they offer. One thing he said that resonated had to do with satellite drift - it's a fact of GPS-based systems and they've programmed in algorithms to account for it. IIRC, you can load up to 4 cameras - the video feeds automatically sync with the data feeds. It's not a cheap system, but the integration they offer is pretty cool.

[lutfy]

Surprised no one ever mentioned PerformanceBox by Race Logic (www.racelogic.co.uk). Car and Driver along with many tire companies and auto manufacturers use it. Have Performance Box and loved it! It seems to be the bees knees outside of the US.

Linky to one in my car. Great for predictive lapping and data analysis after:

http://vimeo.com/user3800046

[ThunderMoose]

Probably late to party but the AIM Solo or SoloDL are very good GPS based timers.

[dogbone]

No doubt that VBox, Race Keeper, Solo and some others are very cool, but they do cost quite a bit of $$$. If you already have an iPhone, Harry's Lap Timer Pro is $19 and the Emprum is $90. Plus, the Emprum works with all location-based apps on the iPhone without any additional drivers or setup, making them much more accurate too. Sometimes I use the Emprum on my bicycle rides with the Strava app. That's very cool. (The Emprum does take longer to get a GPS fix initially then the internal iPhone GPS though.) Anyway, when you're still a noob like me, this is a cost effective way to have fun.

[kartracer12]

I demo the Race Keeper system and loved it. Video integration is built in and they have an iPhone timer display.

[1MOREMOD]

Originally Posted by ThunderMoose

Probably late to party but the AIM Solo or SoloDL are very good GPS based timers.

i have works great for my purposes.

[M3 Montreal]

New update of Harry's LapTimer!

Many new updates including.... Continuous recording instead of every second lap!!

[richardg]

I use ALapHD (unfortunately no longer supported but has everything) and trackmaster on Android. I pair that with an external bluetooth GPS antennae and OBDII reader.

[JonnyTrauma]

Lap timers on android/iphone are only accurate within 1 second. The GPS receivers in these devices have a 1 Hz refresh rate which means it grabs your location once every second. This is only accurate to within ~30 feet assuming you have a strong signal. So yes, this will give you an idea within about 1.3 seconds of accuracy what your lap time is.

You can get an external 10 Hz GPS receiver than will increase the accuracy to 1/10th of a second. That will cost you about $100.

Dedicated GPS laptimers from AIM, Qstarz and Starlane are solid. I use the Qstarz--it is not user friendly but once you figure it out, it works well, is accurate and has great battery life. I've heard battery life is not ideal with the app based solutions so that is something to consider as well.

[dan avoN7]

Originally Posted by JonnyTrauma

Lap timers on android/iphone are only accurate within 1 second. The GPS receivers in these devices have a 1 Hz refresh rate which means it grabs your location once every second. This is only accurate to within ~30 feet assuming you have a strong signal. So yes, this will give you an idea within about 1.3 seconds of accuracy what your lap time is.

Not entirely true for all lap timers.. Harry's Laptimer for example is very accurate for overall lap times even when using the internal GPS @ 1hz. Harry's LapTimer does sophisticated interpolation to calculate the actual point and time the start / finish line was passed. It calculates the trigger‘s perpendicular projection to the virtual line between the GPS fix before and the GPS fix after the trigger. Having calculated this point, the time this point was passed is calculated by linear interpolation from the speed at the fix before, the speed at the fix after, and the distance between these two points. As long as the speed development is near linear, this interpolation yields accuracy beyond 0.01 seconds. This is the reason, why receivers with 1 Hz update rate are fully sufficient for timing and equal accuracy of other technics.

I put my friends VBOX (GPS @ 10hz) in my car for a session at Laguna Seca awhile back and the times were within 0.01 seconds of the times reported with Harry's Laptimer using the internal GPS @ 1hz. I have since added an external GPS @ 5hz to get more accurate readings in turns but for overall lap times the internal GPS works fine

[Longboarder]

Originally Posted by lutfy

Surprised no one ever mentioned PerformanceBox by Race Logic (www.racelogic.co.uk). Car and Driver along with many tire companies and auto manufacturers use it. Have Performance Box and loved it! It seems to be the bees knees outside of the US.

Linky to one in my car. Great for predictive lapping and data analysis after:

http://vimeo.com/user3800046

someone mentioned it already on page 1 (back in 2009).

Yes it's fantastic for getting better (particularly for a novice like me) as it provides an incredible amount of data for analyzing, but it's too expensive for someone just wanting a lap timer.

[M3 Esq]

Just downloaded Track Addict free edition for iPhone 5. Has anyone else used it? I have been fooling around with it on the street and it seems pretty cool. It seems to have very limited functionality but its free so who cares. I will try it at Lime Rock when I'm there on 7/12.

[Nugget]

I use Harry's Lap timer with a bluetooth GPS receiver. I've found it accurate to a 100th of a second when compared with official timing.
It has enough information for a novice like me, plus the video recording and overlay function is very easy to use.
eg.
[u2b]http://youtu.be/6SSqEqOSZso[/u2b]