Harry's GPS Suite Forum

After three consecutive sessions where everything worked perfectly, I'm back in the land of immense frustration, where things again just aren't working, and I have no idea why, as I go through the same procedure every time. Last time, HLT inexplicably spliced over half my laps into one giant, useless lap. Today, the lateral acceleration readings from my session (I actually rode along with a friend in his car while waiting for my new tires to arrive, hoping to be able to compare his driving to mine) are ridiculously low. The speeds recorded throughout his laps appear to be accurate, as are the lap times, and the lap data shows that my XGPS160 was recognized, but the highest lateral acceleration recorded in the fastest corners was about 0.4G, when his car (a fully track-prepped Miata with 9" wide wheels and BF Goodrich G-Force Rival S's ) is easily capable of 1.2 - 1.3G. If fact, other than the speed, all of the data (lineal acceleration, altitude, and to a lesser extent, direction) are incorrect, some by a very wide margin.

I could tell right away by looking at the preview map graphic in his laps that something was wrong. Normally, the g-forces are displayed in green, yellow, and red, depending on the readings, and the higher the g-force, the farther from the track the colors span. On by friend's laps, a thin band of only green outlines the track, and the areas which display the highest g-forces aren't even the fastest corners. So, what HLT is displaying is way out of whack with reality. Please, tell me what may have gone wrong, and more important, tell how I can prevent this from happening in the future. Thanks.

Acceleration is measured by the smartphone's accelerometer and not depending on GPS. As long as you use the automatic acceleration preset (default), LapTimer will expect you to have the device mounted precisely like shown in illustration #4 of LapTimer's Quick Reference (in app). In case you get incorrect measurements for lateral and longitudinal directions, the mounting position will be the reason. If e.g. you mounted the device pointing to you instead of the driver, readings will be wrong. You can work around this by switching the preset, but that's probably something you didn't do. Details are available in "Acceleration Handling" on www.gps-laptimer.de/documentation.

There is some more good news: in case acceleration values were not measured correctly, LapTimer support deriving them from the line driven (and speed). To do this, select the lap from Lap List, scroll down to Data Recordings and press Recalculate ‣ Acceleration. You will get guided through the re-calculation.

In case multiple laps are recorded into one lap, the reason is either a missing / wrong track set, or bad GPS accuracy including temporary "GPS drifts" occurring when atmospheric disturbances / sun eruptions are going on. In case the plot looks accurate in Data Recordings, a GPS drift has been likely the problem, in case it looks grumpy, there has probably a disconnect from the XGPS and the smartphone has a bad GPS reception. You can try to split up the recording into individual laps by selecting the multi lap from Lap List and selecting Recalculate ‣ Verify Lap. In case LapTimer is not able to detect the laps when using the Wide corridor, enlarge it temporarily by adjusting the Wide Corridor Expert Settings (standard is 40 meters, but it can be up to 200 meters).

- Harry

Ah, that explains it - since my friend's Miata doesn't have a mount for an ipad mini, it definitely wasn't in the proper position for collecting data during yesterday's session. So, none of my recent woes have been the fault of Laptimer itself. I learn something new every time I use HLT, although in this case it was very basic.

Now you have me wondering if the mount I have in my car is in the optimal position. Is there a way to post a picture in this forum so I can show you how I have the ipad mini, along with the remote GPS, mounted in my car? I'm guessing I have to post them to a site like Photobucket, right?

You can use the attachment function, it is easier than uploading it to some server and linking it using the [img] tag. Please take care it is a small jpeg file, attachments are limited in size.

- Harry

OK, here's a picture of my ipad mini's mount. The top of the ipad is about 8 cm above the plane of the top of the dash. Hopefully it's high enough, because being quite a bit larger than a smartphone, I'd prefer not to have such a large object obstructing my field of view. You can see the XGPS160 in its black rubber mount on top of the dash, behind and just to the right of the ipad. When everything is working (the satellites are happy, the Gopro hasn't lost its mind, etc.), the set-up works very well. But if you think the height of the ipad is marginal for robust, reliable performance, I could raise it a little. Thanks.

Oh, and replacing the ugly, huge stock steering wheel with something more track-appropriate is on my wish list. Maybe Santa will bring me a nice 350 mm Momo or Sparco wheel this Christmas.

Should be fine.