mc_att_control: remove time constant parameter

Because the parameter does not make sense from a control theory
perspective. Either you have a gain with the unit 1/s or an inverse
gain or time constant with the unit s. But the time constant parameter
was neither bound to any exact unit nor did it apply instead of a gain.
Rather it adjusted multiple gains from rate and attitude control
according to an arbitrary scale. This can only by accident lead to
good tuning.

ROMFS/px4fmu_common/init.d/4080_zmr250

@@ -17,17 +17,15 @@ set PWM_OUT 1234
 
 if [ $AUTOCNF == yes ]
 then
-	param set MC_ROLL_P 2.0
-	param set MC_ROLLRATE_P 0.05
+	param set MC_ROLL_P 2.2
+	param set MC_ROLLRATE_P 0.06
 	param set MC_ROLLRATE_I 0.2
-	param set MC_ROLLRATE_D 0.0015
-	param set MC_ROLL_TC 0.18
+	param set MC_ROLLRATE_D 0.0017
 
-	param set MC_PITCH_P 2.0
-	param set MC_PITCHRATE_P 0.05
+	param set MC_PITCH_P 2.2
+	param set MC_PITCHRATE_P 0.06
 	param set MC_PITCHRATE_I 0.2
-	param set MC_PITCHRATE_D 0.0015
-	param set MC_PITCH_TC 0.18
+	param set MC_PITCHRATE_D 0.0017
 
 	param set MC_YAW_P 1.0
 	param set MC_YAWRATE_P 0.15

src/modules/mc_att_control/mc_att_control_main.cpp

@@ -93,7 +93,6 @@ extern "C" __EXPORT int mc_att_control_main(int argc, char *argv[]);
 
 #define MIN_TAKEOFF_THRUST    0.2f
 #define TPA_RATE_LOWER_LIMIT 0.05f
-#define ATTITUDE_TC_DEFAULT 0.2f
 
 #define AXIS_INDEX_ROLL 0
 #define AXIS_INDEX_PITCH 1
@@ -223,9 +222,6 @@ private:
 		param_t acro_superexpo;
 		param_t rattitude_thres;
 
-		param_t roll_tc;
-		param_t pitch_tc;
-
 		param_t vtol_type;
 		param_t vtol_opt_recovery_enabled;
 		param_t vtol_wv_yaw_rate_scale;
@@ -469,9 +465,6 @@ _loop_update_rate_hz(initial_update_rate_hz)
 
 	_params_handles.rattitude_thres 	= 	param_find("MC_RATT_TH");
 
-	_params_handles.roll_tc			= 	param_find("MC_ROLL_TC");
-	_params_handles.pitch_tc		= 	param_find("MC_PITCH_TC");
-
 	_params_handles.bat_scale_en		=	param_find("MC_BAT_SCALE_EN");
 
 	/* rotations */
@@ -525,36 +518,31 @@ MulticopterAttitudeControl::parameters_update()
 {
 	float v;
 
-	float roll_tc, pitch_tc;
-
-	param_get(_params_handles.roll_tc, &roll_tc);
-	param_get(_params_handles.pitch_tc, &pitch_tc);
-
 	/* roll gains */
 	param_get(_params_handles.roll_p, &v);
-	_params.att_p(0) = v * (ATTITUDE_TC_DEFAULT / roll_tc);
+	_params.att_p(0) = v;
 	param_get(_params_handles.roll_rate_p, &v);
-	_params.rate_p(0) = v * (ATTITUDE_TC_DEFAULT / roll_tc);
+	_params.rate_p(0) = v;
 	param_get(_params_handles.roll_rate_i, &v);
 	_params.rate_i(0) = v;
 	param_get(_params_handles.roll_rate_integ_lim, &v);
 	_params.rate_int_lim(0) = v;
 	param_get(_params_handles.roll_rate_d, &v);
-	_params.rate_d(0) = v * (ATTITUDE_TC_DEFAULT / roll_tc);
+	_params.rate_d(0) = v;
 	param_get(_params_handles.roll_rate_ff, &v);
 	_params.rate_ff(0) = v;
 
 	/* pitch gains */
 	param_get(_params_handles.pitch_p, &v);
-	_params.att_p(1) = v * (ATTITUDE_TC_DEFAULT / pitch_tc);
+	_params.att_p(1) = v;
 	param_get(_params_handles.pitch_rate_p, &v);
-	_params.rate_p(1) = v * (ATTITUDE_TC_DEFAULT / pitch_tc);
+	_params.rate_p(1) = v;
 	param_get(_params_handles.pitch_rate_i, &v);
 	_params.rate_i(1) = v;
 	param_get(_params_handles.pitch_rate_integ_lim, &v);
 	_params.rate_int_lim(1) = v;
 	param_get(_params_handles.pitch_rate_d, &v);
-	_params.rate_d(1) = v * (ATTITUDE_TC_DEFAULT / pitch_tc);
+	_params.rate_d(1) = v;
 	param_get(_params_handles.pitch_rate_ff, &v);
 	_params.rate_ff(1) = v;
 

src/modules/mc_att_control/mc_att_control_params.c

@@ -39,34 +39,6 @@
  * @author Anton Babushkin <anton@px4.io>
  */
 
-/**
- * Roll time constant
- *
- * Reduce if the system is too twitchy, increase if the response is too slow and sluggish.
- *
- * @unit s
- * @min 0.15
- * @max 0.25
- * @decimal 2
- * @increment 0.01
- * @group Multicopter Attitude Control
- */
-PARAM_DEFINE_FLOAT(MC_ROLL_TC, 0.2f);
-
-/**
- * Pitch time constant
- *
- * Reduce if the system is too twitchy, increase if the response is too slow and sluggish.
- *
- * @unit s
- * @min 0.15
- * @max 0.25
- * @decimal 2
- * @increment 0.01
- * @group Multicopter Attitude Control
- */
-PARAM_DEFINE_FLOAT(MC_PITCH_TC, 0.2f);
-
 /**
  * Roll P gain
  *