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DIY GPS Questions

KartgpsKartgps
in DIY builds
Hello everyone,

Me and a group of friends are building a DIY GPS lap timer for go karting. It is the first time we are playing with GNSS but we are loving it! Our setup is simple: a ublox SAM M8Q connected to Racechrono to record data. We are using the integrated ceramic antenna of the GNSS module inside a thin box, no external antennas.

Overall, results have been good. However, we feel we can go further on precision and we have some questions:

- Is it supposed to lock on 10Hz? We have our receiver configured to lock on GPS + GLONASS and output the bare minimum of messages. Our baudrate is set to 115k (both on the receiver and devkit). All our parameters on Racechrono are great (DOP <1). However, the update rate drops constantly from 10Hz to around 7Hz even when connected to 15 satellites. Is this normal? Is the update rate supposed to be locked at 10Hz at all times?

- What is the best dynamic model for our use case? We are currently using "pedestrian" because we thought the more sensible, the better. However, our lap tracing around the track is very erratic and full of sharp lines (no smoothness). We are also missing some gates (start/finish lines, sectors) on some laps because the "line" is way off the track. Are we correct to think this may be linked to our incorrect dynamic model?

- Strange inconsistency? Most laps our measurements are very precise, off by one or two hundreds compared to official timing and timing from professional devices. However, some laps are randomly way off (half a second). Is it possible we are having errors? Are there ways to measure the consistency of data across a complete session? What kind of configurations would you suggest we change and retest to maintain consistency across a full session?

Thank you in advance for any help!

Comments

  • gps_netgps_net
    1. It should work. I used multiple m8 gps and I do not have such problem. How you transmit from gps to racechrono? via bluetooth? BLE or Bluetooth classic? in real time? 115200 sounds ok when only necessery nmea frames left. which nmea messages do you have enabled?
    2 and 3. I do not think this is related to dynamic model. I used often "automotive" (motorcycle racing) and do not have such issues. I think there are 2 things to blame : antena placement (or in general reception - which not always can be fixed because of relections), and no proper gates(to small - you can extend them to cover a little bit outside track to catch if gps is slightly "off". Inconsistancy: I think this is also probably becuse of reception. Which antena you use(how big)?
    I tested all : m6, m7, m8 and m9 gps recivers, and some china (ebyte)one. in 2024 I will test m10 :)
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