Bad position when moving around with 'moving base'

Q&A forumBad position when moving around with 'moving base'
django122 asked 8 months ago

Hello, after our evening session with skype and some corrections (many thanks for this), everything works fine. But now i am testing it outside and i simulate the work for what it is designed. After 6 minutes the system has a RTK-fix and it writes a position which is 20-30 centimeter beside and doesn\’t change anymore. Should be better, but it is ok. Now i move with the whole system to an other position. I didn\’t switch of both systems. After a short time it has a fix again, but the position is far away from all. Some meters. My configuration is moving base. Moving means moving, or is it wrong? One user ask the question, what does it means, if the base switch into time-mode. You said, do not move the base after switch on the system. But what, if i have a moving base which switches to time-mode? I want to go around. Could it be, that in time-mode the correction data is from the old position and is not up to date? What does it realy mean: time-mode? So in the moment i hav to switch off the base ervery time i move. Because it is fixed inside a car together with other equipment it is not so nice to switch all off and on again. May be you have a solution or an answer for my question. Matthias

Ardusimple Staff replied 8 months ago

The concept of TIME mode is only valid for Static Base station. It means that the base station has a fixed position (even if this position might have an offset). When using a base station in this configuration, it’s important to not move the base station once it’s powered. Corrections from a static base station are valid for a few seconds.

A moving base station is different. It’s a base station that is constantly moving. For this case, the simpleRTK2B should not be configured to go into TIME mode, but just enable RTCM output of the message of moving base. See
The corrections of a moving base station are only valid for a few milliseconds, because the base station is moving.
In a wired-connection is not a problem, but in a wireless movingbase-rover setup, the faster you move the more error your system will have.

clive1 replied 8 months ago

Yes definites shouldn’t be going into TIME mode, suggests something amiss with UBX-CFG-TMODE3, you don’t want a fixed location, or survey-in enabled there.
The Moving Base also should NOT be outputting message 1005, it should be using 4072.0 in place of that.

The separation of the antennas in a dual configuration really needs to be a metre or more. For transit of RTCM3 data I have ZED#1-UART#2-TX directly wired to ZED#2-UART#2-RX, with a high baud rate to reduce the latency, and using MSM7 messages.
One of the test platforms is a small gas/petrol powered zero turn vehicle, with each rear-wheel driven independently via a hydro-drive unit.

Watch also the update rate, I’m using 5 Hz, the ZED-F9P can perhaps get to 8 Hz in moving-rover, and the ZED-F9H should be able to hit 10 Hz