moving base at >1 Hz

Q&A forumCategory: Questionsmoving base at >1 Hz
kylerlaird asked 4 weeks ago

I’m starting to get some working code.  Today I reduced CFG-RATE-MEAS (0x30210001) on the main board below 1000 ms (1 Hz).  When I do that, I get a lot of invalid RELPOSNED messages (flags=0x01).  Every second or so (sometimes twice in a row) I get a valid one but the acc_heading is around 8 degrees.  When I bump the period back up to 1000 ms, I get consistent valid measurements with an acc_heading around 0.25 degrees.  When I push to 1100 ms, I get invalid readings again.
I’m guessing that this has to do with being out of sync with the Lite board.  I’m going to change it, too.  I’m mostly documenting here but I welcome insight.

Is there somewhere that I should have read about this?  I’m hoping I can push it to 20 Hz.

kylerlaird replied 4 weeks ago

Well, that didn’t go as easily as I hoped. I tried connecting to the USB closer to the Lite board in order to reconfigure it. It didn’t go. I was able to query the CFG-RATE-MEAS one time but I got garbage otherwise. I have some learning to do…

2 Answers
clive1 answered 4 weeks ago

In a dual-up configuration I have the ArduSimple units working at 5 Hz and 10 Hz
Without high baud rates, limited messages, and some systemic understanding of time, I suspect latency, and its inconsistency, will be the primary source of positional error at 20 Hz.
https://www.u-blox.com/sites/default/files/ZED-F9P-MovingBase_AppNote_%28UBX-19009093%29.pdf

kylerlaird replied 4 weeks ago

I agree that pushing to 20 Hz is not likely to go well, and isn’t really necessary for me.

I decided to go to 5 Hz but increase the RELPOSNED “rate” to 5 (so it would remain at 1 Hz). Now every other reading is invalid (“0.0 degrees +/- 180 degrees”).

kylerlaird replied 4 weeks ago

I started tracking the i_tow of the messages I’m receiving. I now see that the invalid RELPOSNED messages are not at the top of the second.

I turned off RELPOSNED and investigated the effects of changing CFG-RATE-MEAS (0x30210001). It is not working the way I expect. At 1000 ms, everything is in sync. Any other settings seems to cause it to go crazy. If I set it to 100 ms, I get PVT readings at x.0 seconds and x.2 (then a 0.8 second wait). At 500 ms, readings sometimes come at x.0 and sometimes at x.5, often with a second between readings.

Ardusimple Staff replied 3 weeks ago

Not sure if you did, when working in moving base configuration, both moving base and rover need to be configured at the same navigation rate.

vincemic answered 3 weeks ago

If someone has moving base working with a simpleRTK2B and simpleRTK2BLite, could you save the configuration from the simpleRTK2b and post it here?

clive1 replied 3 weeks ago

https://www.ardusimple.com/question/moving-baseline-configuration-file/
One would be a Rover (reports relative placement of antennas), the other a Moving Base (reports location) feed with data from the Fixed Base