Pixracer pro and mRo GPS u-Blox Neo-M9N

Hey, I am using Pixracer pro and mRo GPS u-Blox Neo-M9N. I want to go up to 30 m/s. I heard I have to change GPS update rate. can ı do GPS_RATE_MS 20 Hz? I can not understand GPS_Rate_MS Params explanation. “Controls how often the GPS should provide a position update. Lowering below 5Hz(default) is not allowed. Raising the rate above 5Hz usually provides little benefit and for some GPS (eg Ublox M9N) can severely impact performance.” What is the meaning of that? Thx

You need to raise the UART speed (115200 at 10Hz with GPS-GLONASS-GALILEO-SBAS is fine). You can also set the rate at 25Hz (use UBlox utility) but you need a high speed serial to get all data.

Have a look at https://www.u-blox.com/sites/default/files/NEO-M9N_Integrationmanual_%28UBX-19014286%29.pdf for a better understanding.

Better accuracy (Max position deviation = Small) is with “Pedestrian” dynamic platform model (usable under 30m/s velocity).

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I will change the platform model as a pedestrian but should I change the GPS_RATE_MS parameter on Pixhawk. and why should ı change the GPS baud rate as 115200

Change UART rate from 38400 to 57600 or best 115200 to avoid buffer overflow and loss off data.

There is also another problem I was not aware: at 10Hz refresh rate, number of used sats maxed at 16 (even if more are usable). At 5hz I manage to get more than 20, under a roof window and alf sky not visible.

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This is a known issue with the M9N. It tracks less satellites at 10hz than it does at 5hz. Please leave it at 5hz for the best performance.


if I use M8N. Can I use 15-20 Hz update rate?

but I can’t use 5Hz at high speed. Like 30 m/s. or can I use

For the m8n, at 10Hz you can only use a single Constellation.

So, I would say yes and no.

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