Weird lap times?

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Weird lap times?

Postby clovisjacob » Mon Dec 22, 2014 11:54 pm

Hi, I've just got the TrackAddict HD. I really like the idea of it, but I have a question:

I took it to the track last weekend and tested it for the first time. I was with two other friends and they both had their own lap timer apps.

After the first session (8 laps), we all went back to the pits and compared our data from the different apps. TrackAddict was the only one that managed to get accurate lap times. So, my two friends rushed to download TrackAddict for their next sessions and we tried it again everyone using TrackAddict. Surprisingly, after the first session we never managed to get accurate lap times again (or at least lap times that make sense). After the first session (5 laps with average of 2min40sec) we were all getting weird lap times.

How we used the app:
Track: Sydney Motorsports Park - Full Extended circuit (I managed to select Sydney Motorsposts Park but not the Full extended circuit)
Category: Supersport bikes (motorbike)
Phone/App: iPhone 6/iOS 8/TrackAddictHD
Device placed in: Chest pocket, Left Hand Side, inside the leathers

The first session was very accurate: - GPS quality in all laps at around: 30.0m / 11.5
6 laps, with the 1st and 6th laps being longer/faster than others as we start from the pits. That makes sense and I can see in the map that the last lap was just me entering in the pit lane!
4 real laps with an average time of 2min45sec (consistent with manual and professional lap timer we had)
Fast lap of 2min41sec (also consistent with other lap timers)

But for the second and third sessions I (and the others) were getting weird lap times and fewer laps. For instance, I've got 3 laps, being one of 8min and other of 5min and it was supposed to be the same amount of laps (6 laps). Same method was used at all times. Same GPS quality for all sessions but weird times.

Settings of the app:
Mode: circuit
Track: Sydney Motorsports Park
video: Off
--more options--
OBD: off
GPS: Enhanced
Mode: Reliable
Units: km/h
GoPro: Off
Online: Off
Video: 1080p

Screenshots:
Accurate session: https://drive.google.com/file/d/0B76Hhe ... sp=sharing
Accurate Session 2: https://drive.google.com/file/d/0B76Hhe ... sp=sharing
Settings of the app: https://drive.google.com/file/d/0B76Hhe ... sp=sharing
Settings 2: https://drive.google.com/file/d/0B76Hhe ... sp=sharing

Is that something we are doing wrong, or we can't get proper lap times every time? I'm very excited with the App and RaceRender, that's why I want to make it work. Please let me know, love the idea of the app!

Cheers,

Clovis
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Posts: 2
Joined: Mon Dec 22, 2014 10:58 pm

Re: Weird lap times?

Postby RaceRender LLC » Mon Dec 29, 2014 6:23 pm

Hello,

GPS reception would appear to be the problem here, which is almost always the case for larger lap time inaccuracies or inconsistencies. When a smartphone is placed in a pocket, its GPS receiver would not have an unobstructed view to the sky, and it would be introducing additional error because it is also moving with the rider's body rather than with the vehicle. Although this can still appear to produce reasonably acceptable data for some parts of the track, or in lower speed testing, it often will not provide consistent quality around the entire track for every lap.

The GPS is able to recognize that it has a problem in some situations, and it evidently did in this case... In the second screenshot, it shows a GPS Quality of 30.0 / 11.5 meters for that selected lap, indicating that iOS believes that at least one data point could have been off by as much as +/- 30 meters. Higher numbers indicate a higher amount of error. In reality, it probably wasn't really quite that far off (iOS rounds up to 5, 10, or 30... nothing in between), but it does indicate that the GPS at least recognized some increased level of error. An accuracy of 10 meters is the norm for iPhones, with 5 being possible under more ideal conditions, and the average can often be between the two. In this case, the 11.5 meter average indicates that it was probably operating between the 10 and 30 levels, with a significant number of them being at 30. I did the math for the lap that was displayed, and it works out to about 7-8% of that lap's data points having a suspected error, which is high.

To improve this situation, I would recommend finding a place where you can securely and safely mount the iPhone, and where it also has a good line-of-sight to the sky. That's of course easier said than done on a motorcycle, but the tail or rear cowl section is often your best bet. A simple plastic cover generally doesn't cause much problem for GPS; the main concern is that there's no metal between the device and the sky, as that can cause multi-path reception errors, which don't always show up in the reported GPS quality levels. Beyond that, another option would be to use an external GPS add-on, like the Dual XGPS160 or XGPS150, because those provide better GPS accuracy, reception, sample rate, and can have different mounting options... they connect over Bluetooth and will work with TrackAddict, as well as most other GPS-enabled iOS apps.
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Re: Weird lap times?

Postby clovisjacob » Tue Dec 30, 2014 5:07 am

Thanks a lot RaceRender, I did suspect that. I'll try this on my next trackday. A better GPS device is definitely on my list. I'll keep you guys updated. Nice work with the app!

Cheers

Clovis
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Posts: 2
Joined: Mon Dec 22, 2014 10:58 pm


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