IMU data integration to moving baseline M8P

0 votes
Has anyone been able to integrate IMU data with an M8P rig?

- I have not been able to read any built in IMU data (since it says there isn't one present). Does anyone have data that contradicts this? Or know definitively if there's an IMU on the die itself?

- Integrate an M8U unit. Can anyone speak to the possibility of feeding the M8U raw UBX data from the rover and have the IMU and EKF on the M8U work? Or does it absolutely need it's own antenna?

The other option is to implement an EKF on separate chips and integrate a completely separate IMU.



by STR-Alorman asked Mar 9
0 votes
Let's unpack this a bit.

The NEO-M8P and M8U use the same UBX-M8030 chipset. The M8U contains discrete accelerometer/gyro parts on the PCB of the module. These are read at ~99Hz as I recall. Raw data from these is available. A High Navigation Rate (HNR) solution is developed from these and the GPS solution, at rates of 10 or 20 Hz.

RTK is a geometry based solution, solving for the phase-center of the antenna, for wavefronts of the radio signal striking two different locations with an instantaneously frozen displacement with respect to each other. The orientation and rotation of the antenna isn't much help here but arguably discernable at a sub mm level.

The M8U should be able to output "raw measurements" if you wanted to solve for RTK with an external library you could probably take that tack..

You can split an antenna feed between multiple receivers, they are solving for a notional location point that typically floats above the antenna element. The M8U expects to share a rigid attachment to the same structure that holds the antenna so they both perceive the same motion.
by clive1 answered Mar 10
Thanks for the answer. I knew I threw a lot out there. Commencing unpacking:

- Thanks for confirming the M8P and U use the same chipset (does the T as well?)

- Raw data should be transmitted over UBX sentences, correct?

- No desire to solve RTK with external software. Tried that with RTKLIB (me and everyone else here). Got better results with two M8Ps.

I'm planning to add a Teensy chipset to do the haversine math between the  base and rover and output an NMEA $GPHDG sentence. If I can integrate an EKF for rapid changes in heading based on the IMU data passed to the Teensy, perfect. The IMU data I seek is more to account for fast changes in heading shift than anything else.