This patch reduces the level of 5Hz and 10Hz 'pulsing' heard in motors due to GPS and altimeter fusion which cause a small 5Hz and 10Hz ripple on the output under some conditions. Attitude, velocity and position state corrections from GPS, altimeter and magnetometer measurements are applied incrementally in the interval from receiving the measurement to the predicted time of receipt of the next measurement. Averaging of attitude state corrections is not performed during periods of rapid rotation.
Time stamps are now explicitly initialised to the current IMU time to avoid unwanted activation of timeout logic on filter start and the various calls to the hal.scheduler->millis() object have been consolidated.
Unused variables have been removed
If the inertial solution velocity or position needs to be reset to the GPS, the stored state history for the corresponding states should also be reset.
Otherwise the next GPS measurement will be compared to an invalid previous state and will be rejected.
The position state should be reset to a GPS position corrected for velocity and measurement latency. This will make a noticeable difference for high speed flight vehicles, eg 11m at 50m/s
Re-initialisation of the magnetic field states and yaw angle is now only performed a maximum of two times after start-up.
Once when coming out of static modefor the first time (first arm event)
Again (for copter only) when the altitude gain above the arming altitude exceeds 1.5m
this prevents magnetic interference present at arming (eg arming on a metal roof)from corrupting the magnetic field states enough to cause bad heading errors and toilet bowling on copter
(Plane Only) If the yaw and GPS heading disagree by more than 45 degrees on takeoff, then the magnetometer is declared as failed. The heading is then reset based on the difference between GPS ground track and stgate velocity vector.
Magnetometer fusion uses corrected data and bias states are initialised to zero. This allows the compass to be switched in flight.
For persistent compass errors that trigger a timeout, the compass is not permanently failed, however for non-forward fly vehicles the compass weighting is reduced.
The GPS glitch offset was being zeroed during position resets. This caused the filter to reject subsequent GPS measurements if the GPS error persisted long enough to invoke a timeout and a position reset.
GPS measurement variance is doubled if only 5 satellites, and quadrupled if 4 or less.
The GPS glitch rejection thresholds remain the same
This will reduce the impact of GPS glitches on attitude.
The uncertainty in acceleration is currently only scaled using horizontal accelerations, however during vertical plane aerobatics and high g pullups, misalignment in angles can cause significant horizontal acceleration error.
The scaling now uses the 3D acceleration vector length to better work during vertical plane high g maneouvres.
This error was found during flight testing with 8g pullups
If the inertial solution velocity or position needs to be reset to the GPS or baro, the stored state history for the corresponding states should also be reset.
Otherwise the next GPS or baro measurement will be compared to an invalid previous state and will be rejected. This is particularly a problem if IMU saturation or timeout has occurred because the previous states could be out by a large amount
The position state should be reset to a GPS position corrected for velocity and measurement latency. This will make a noticeable difference for high speed flight vehicles, eg 11m at 50m/s.
Flying aerobatics with Trad Heli has shown that the divergence check can be false triggered when large magnetometer errors and GPS dropouts are present.
This can also happen with multi rotors if large yaw rates are present.
This was an unintended consequence of the ekfsmoothing patch which improved filter stability during high rate manoeuvres, but made the divergence test more sensitive.
This patch reduces the level of 5Hz and 10Hz 'pulsing' heard in motors due to GPS and altimeter fusion which cause a small 5Hz and 10Hz ripple on the output under some conditions. Attitude, velocity and position state corrections from GPS, altimeter and magnetometer measurements are applied incrementally in the interval from receiving the measurement to the predicted time of receipt of the next measurement. Averaging of attitude state corrections is not performed during periods of rapid rotation.
Time stamps are now explicitly initialised to the current IMU time to avoid unwanted activation of timeout logic on filter start and various calls to the hal.scheduler->millis() object have been consolidated.
This allows a compass that has been declared failed, possibly because of
external disturbances (eg movement of hatches, proximity of tools, etc)
to be given a second chance when the vehicle is armed.
priseborough
Jonathan Challinger
Andrew Tridgell
Randy Mackay