Combining Single Antenna GPS + IMU

Hardware Antenna Placement and steering algorithm
50

  • Why is the min roll filter value in v5 two ? Cant see any filter in v4 roll data.
    Because at 2 it means almost nothing. Even at 50 you can barely tell there is a filter. It is not linear.

  • Why do we have the IMU data in the steering message when it can go seperately with only a .ino program change (for the current uses that dont want to build external IMU)
    Because many systems are already running on the edge.

  • Why is the external IMU program only running at 100msec
    Same answer as above. You can run it at 50 msec, but it will still be wrong. You can fiddle with it but it will never work as well as intercepting the nmea and timing the imu with the fix time.

The odd part is, you would think it would work better then it does but the antenna is on the wrong end of the sin, huge position change for very little roll values.

At 3m height:
1 deg = 5cm
2 deg = 10.4 cm
3 deg = 15.7 cm
4 deg = 21 cm

Now at 3.5 kmh ( 1 m/sec) fixes at 10 cm apart. The tractor takes almost no time to wiggle back and forth a few degrees, add to that the timing is off up to 100 msec - or even 50 msec if running at 20 hz and it is a complete disaster compensation adding when it should be subtracting and vice versa.

The imu must be taken at exactly the time the gps is doing its fix and putting the imu on the steer board or as an external imu will not give satisfactory performance.

Add to that windows - delays and different timings from fix to fix in AgIO and AOG and serial ports and you do the only sane thing - filter the roll so it works on sidehills.

At least this is my experience. I think what is maybe hard to grasp is how critical GPS position correction is. It has to be dead on.

Good to hear from you again Charles! Yes, PAOGI has gotten pretty old. PANDA is much the same except it excludes dual and has imu. Parsed the same way, just fills in what is required for single with imu so without any settings AOG knows it is single.

With current boards having the GPS and imu on the same board talking to a Teensy powerhouse, it simply becomes a software solution to time the imu and fixes.