Logging with MAVLink on high frequencies

Ground Control Software MAVLink
1

Hi,

I want to read out the SR1_EXTRA1 at a rate of 30Hz. So far everything works, but the actual timing jitter is extremely high. Sometimes I receive frames after 5-10ms some other times it takes over 40ms until I receive a new one.

I know that the telem port was never intended to be used at such high speeds, but I would still like to achieve a more accurate timing. Is there maybe a better method on doing that? Do you have any recommendations? I’m using a Pixfalcon Mini with the ArduPlane firmware. Any help would be appreciated.

BTW Baud is at 115200 and all other telem ports are disabled.

2

Are you using ChibiOS master? did you use pymavlink\telemetry_datarates.py script to test if that is a feasible datarate?

3

Where can I see the RTOS that the pixfalcon is using?

as for the file you mentioned https://github.com/ArduPilot/pymavlink/blob/master/tools/mavtelemetry_datarates.py#L61
it’s showing 2Hz as datarate, but even the default is 10Hz - soo this seems to not really give an indication.

I would also be fine with triggering the internal logging, but I have the impression that it is as unreliable.

4

You can run that script and test what telemetry rates are possible.
In your case , possible are telemetry rates that do not sum up more than 115200
The tool does the sum for you.

5

Okay I’ll give this a shot. However what timing accurarcy can I expect from an Pixhawk v2 design?

6

The tool let’s you test “what if” scenarios, you still have to set the parameters one-by-one on the flight controller by hand.
With the ChibiOS version the timing accuracy is really good.

1 Like
7

Indeed @amilcarlucas your tip with ChibiOS was good. Amazed how much better timing is now. Thanks a lot!