ekf2: Add parameters to tune accelerometer bias learning

These parameters enable the accel bias limiting and learning inhibit logic in the ecl EKF to be easily tuned during testing and replay.

src/modules/ekf2/ekf2_main.cpp

@@ -297,6 +297,12 @@ private:
 	_mag_bias_saved_variance; ///< Assumed error variance of previously saved magnetometer bias estimates (mGauss**2)
 	BlockParamFloat _mag_bias_alpha;	///< maximum fraction of the learned magnetometer bias that is saved at each disarm
 
+	// EKF accel bias learning control
+	BlockParamExtFloat _acc_bias_lim;	///< TODO
+	BlockParamExtFloat _acc_bias_learn_acc_lim;	///< TODO
+	BlockParamExtFloat _acc_bias_learn_gyr_lim;	///< TODO
+	BlockParamExtFloat _acc_bias_learn_tc;	///< TODO
+
 	// Multi-rotor drag specific force fusion
 	BlockParamExtFloat _drag_noise;	///< observation noise variance for drag specific force measurements (m/sec**2)**2
 	BlockParamExtFloat _bcoef_x;		///< ballistic coefficient along the X-axis (kg/m**2)
@@ -310,8 +316,8 @@ private:
 	BlockParamFloat _K_pstatic_coef_y;	///< static pressure position error coefficient along the Y body axis
 	BlockParamFloat _K_pstatic_coef_z;	///< static pressure position error coefficient along the Z body axis
 
-	// airspeed mode parameter
-	BlockParamInt _airspeed_disabled;
+	BlockParamInt _airspeed_disabled;	///< airspeed mode parameter
+
 };
 
 Ekf2::Ekf2():
@@ -410,6 +416,10 @@ Ekf2::Ekf2():
 	_mag_bias_id(this, "MAGBIAS_ID"),
 	_mag_bias_saved_variance(this, "MAGB_VREF"),
 	_mag_bias_alpha(this, "MAGB_K"),
+	_acc_bias_lim(this, "EKF2_ABL_LIM", false, _params->acc_bias_lim),
+	_acc_bias_learn_acc_lim(this, "EKF2_ABL_ACCLIM", false, _params->acc_bias_learn_acc_lim),
+	_acc_bias_learn_gyr_lim(this, "EKF2_ABL_GYRLIM", false, _params->acc_bias_learn_gyr_lim),
+	_acc_bias_learn_tc(this, "EKF2_ABL_TAU", false, _params->acc_bias_learn_tc),
 	_drag_noise(this, "DRAG_NOISE", true, _params->drag_noise),
 	_bcoef_x(this, "BCOEF_X", true, _params->bcoef_x),
 	_bcoef_y(this, "BCOEF_Y", true, _params->bcoef_y),

src/modules/ekf2/ekf2_params.c

@@ -1162,3 +1162,53 @@ PARAM_DEFINE_FLOAT(EKF2_PCOEF_Y, 0.0f);
  * @decimal 2
  */
 PARAM_DEFINE_FLOAT(EKF2_PCOEF_Z, 0.0f);
+
+/**
+ * Accelerometer bias learning limit. The ekf delta velocity bias states will be limited to within a range equivalent to +- of this value.
+ *
+ * @group EKF2
+ * @min 0.0
+ * @max 0.8
+ * @unit m/s/s
+ * @decimal 2
+ */
+PARAM_DEFINE_FLOAT(EKF2_ABL_LIM, 0.4f);
+
+/**
+ * Maximum IMU accel magnitude that allows IMU bias learning.
+ * If the magnitude of the IMU accelerometer vector exceeds this value, the EKF delta velocity state estimation will be inhibited.
+ * This reduces the adverse effect of high manoeuvre accelerations and IMU nonlinerity and scale factor errors on the delta velocity bias estimates.
+ *
+ * @group EKF2
+ * @min 20.0
+ * @max 200.0
+ * @unit m/s/s
+ * @decimal 1
+ */
+PARAM_DEFINE_FLOAT(EKF2_ABL_ACCLIM, 25.0f);
+
+/**
+ * Maximum IMU gyro angular rate magnitude that allows IMU bias learning.
+ * If the magnitude of the IMU angular rate vector exceeds this value, the EKF delta velocity state estimation will be inhibited.
+ * This reduces the adverse effect of rapid rotation rates and associated errors on the delta velocity bias estimates.
+ *
+ * @group EKF2
+ * @min 2.0
+ * @max 20.0
+ * @unit rad/s
+ * @decimal 1
+ */
+PARAM_DEFINE_FLOAT(EKF2_ABL_GYRLIM, 3.0f);
+
+/**
+ * Time constant used by acceleration and angular rate magnitude checks used to inhibit delta velocity bias learning.
+ * The vector magnitude of angular rate and acceleration used to check if learning should be inhibited has a peak hold filter applied to it with an exponential decay.
+ * This parameter controls the time constant of the decay.
+ *
+ * @group EKF2
+ * @min 0.1
+ * @max 1.0
+ * @unit s
+ * @decimal 2
+ */
+PARAM_DEFINE_FLOAT(EKF2_ABL_TAU, 0.5f);