After a few years of use of the Qstarz GPS products (4x BT-Q818XT and 2x BT-Q1000eX) for race track analysis I found a problem. For years I'm trying to convince the Qstarz tech departement of the error in their heading algorithm, but they are not resolving this in a proper way.
I hope more complaints from other users will help resolving this issue, as I like this cheap GPS solution and normally very accurate low filtered output.
When translating the values in the NMEA messages into speed, acceleration and lateral acceleration in e.g. RaceChrono I have found some strange numbers and graphs.
When turning right and going through the north at 360 degrees the heading drops from 359 to just over 0 degrees; see track layout on the upper part of the graph.
The algoritm in the Qstarz products that is calculating speed and heading seems to have a problem around this 360 degrees point.
The red/yellow/green racing line is correctly plotted: a fluent line through the corner.
The lines plotted for
• Longitudinal acceleration/deceleration
are also plotted correctly.
But the line for Lateral force (green) has 2 strange spikes (in the area that is marked red):
First it spikes up from -0,9 G to -0,2 G and then a big negative spike up to 2,0 G
This caused by the algorithm that is calculating the heading.
Take a look at a part of a BT-Q1000eX export file:
You see the heading is stuck to 358.91 for 4 lines (4/10 of a second) , and then jumps to 10.15
As RaceChrono is using these values (and not recalculating the heading and speed using the locations),
the values for the lateral acceleration at those points are very starnge...
I can reproduce this problem in most Qstarz devices when looking at exports.
How can I add graphs to this post, as this would really make this problem easier to understand?