problems with RaceChrono+Nokia5800+BT-Q818XT on go-kart

Hello all,

I am an Italian member, so I am sorry for my English. I am facing some problems with the equipment listed on the topic title. The symptoms of the malfuntion are following:
most of the laps the route does not match the track. It is like the satellites are lost and when the position is found, the route becomes a sort of stright line from the last detected position and the new position, cutting the curve. The strange thing is that some laps are quite good and the timing is precise (I have also a standard automatic chrono on the steering). Many other times, the route is very strange with big jumps on the track. Setting the baudrate on default, the result is useless at all. Using the baudrate at 115200 as requested by the bluetooth GPS receiver manual things are better but with strange errors which lead the timing being useless most of the laps. At present, I can only put the GPS receiver in a pocket of the suit and the smartphone in another poscket. Does anyone encoutered the same problems? Could be the equipment not suitable for kart timing? Can I do something to improve GPS receiver + smartphone performance? Thanks for helping me. Bye.


  • "At present, I can only put the GPS receiver in a pocket of the suit "
    ^Thats the problem. Your body and arms causes electromagnetic interference/ blocks gps signals.
    Use duct tape and put the gps receiver on top of your helmet, and test again.
  • Thank you Deadslow. I will follow your instruction next time I'll be on track. Just a final question. I tested the gps receiver on my car. I noticed that the position precision was 1.35 on average when 7 satellites were fixed, sometimes 0.90 with 9 or 10 satellites and sometimes 2.something with less then 7 I believe. What daes this means? Are these numbers the error in meters from the real position? In your opinion, are those precision values good enough for a good tracking and timing also on a kart track (which is characterized by short ray curves)? Thank you for your patience. Bye
  • Sorry Deadslow for being so lazy. I found an article on line about DOP (see my previous comment). The link is So according to the article, the precision at the DOP values shown by RaceChrono should be very good. Thank you again for helping me to understand what mistakes I have made during my first test on track. Bye
  • Hello Deadslow. Tonight I tested the Qstarz BT-Q818XT gps receiver on track. I have built a seat with open roof for the GPS receiver on the kart. The DOP was 1.30 on average. The tracking was much more precise than the last time I went on track. The signal seems continuous and the route looks smooth (without impossible paths).
    Also the precision on lap timing looks good enough.
    The mismatch between the automatic chrono I have on the kart (which is activated by real traps on the track) and the Racechrono timing on a single lap can vary between 0.02 seconds to 0.08 seconds. In your opinion, is it an acceptable gap or it is possible to improve, according to your experience? Thank you.
  • Hi, 0.02 - 0.08 is as good as it will ever get.
  • Thank you very much Aol. Looking at other discussions on the web about this topic, I noticed that most people experienced DOP values close to 0.5 on average. When I am lucky I can see 0.9, but most of the times I see about 1.35 with 10HZ updating frequency (no DGPS permitted) and about the same at 5HZ which should allow DGPS function and updated satellites route data downloaded from the web. I know that DOP depends on several parameters such as satellites positions on my head etc. I was just wondering if the DOP values I see are common or I should expect something better from this GPS receiver model (BT-Q818XT). Thank you for your patience.
Sign In or Register to comment.