multirotor_pos_control: cleanup and fixes

src/modules/multirotor_pos_control/multirotor_pos_control.c

@@ -251,7 +251,7 @@ static int multirotor_pos_control_thread_main(int argc, char *argv[])
 	}
 
 	pid_init(&z_pos_pid, PID_MODE_DERIVATIV_SET, 0.02f);
-	thrust_pid_init(&z_vel_pid, params.z_vel_p, params.z_vel_i, params.z_vel_d, -params.thr_max, -params.thr_min, PID_MODE_DERIVATIV_CALC_NO_SP, 0.02f);
+	thrust_pid_init(&z_vel_pid, 0.02f);
 
 	while (!thread_should_exit) {
 
@@ -265,18 +265,18 @@ static int multirotor_pos_control_thread_main(int argc, char *argv[])
 			/* update params */
 			parameters_update(&params_h, &params);
 
+			/* integral_limit * ki = tilt_max / 2 */
+			float i_limit;
+
+			if (params.xy_vel_i > 0.0f) {
+				i_limit = params.tilt_max / params.xy_vel_i / 2.0f;
+
+			} else {
+				i_limit = 0.0f;	// not used
+			}
+
 			for (int i = 0; i < 2; i++) {
-				pid_set_parameters(&(xy_pos_pids[i]), params.xy_p, 0.0f, params.xy_d, 1.0f, 0.0f);
+				pid_set_parameters(&(xy_pos_pids[i]), params.xy_p, 0.0f, params.xy_d, 0.0f, 0.0f);
-				/* use integral_limit_out = tilt_max / 2 */
-				float i_limit;
-
-				if (params.xy_vel_i > 0.0f) {
-					i_limit = params.tilt_max / params.xy_vel_i / 2.0f;
-
-				} else {
-					i_limit = 0.0f;	// not used
-				}
-
 				pid_set_parameters(&(xy_vel_pids[i]), params.xy_vel_p, params.xy_vel_i, params.xy_vel_d, i_limit, params.tilt_max);
 			}
 
@@ -471,6 +471,7 @@ static int multirotor_pos_control_thread_main(int argc, char *argv[])
 							} else {
 								local_pos_sp.z = local_pos.ref_alt - global_pos_sp.altitude;
 							}
+
 							/* update yaw setpoint only if value is valid */
 							if (isfinite(global_pos_sp.yaw) && fabsf(global_pos_sp.yaw) < M_TWOPI) {
 								att_sp.yaw_body = global_pos_sp.yaw;

src/modules/multirotor_pos_control/thrust_pid.c

@@ -43,22 +43,22 @@
 #include "thrust_pid.h"
 #include <math.h>
 
-__EXPORT void thrust_pid_init(thrust_pid_t *pid, float kp, float ki, float kd, float limit_min, float limit_max, uint8_t mode, float dt_min)
+#define COS_TILT_MAX	0.7f
+
+__EXPORT void thrust_pid_init(thrust_pid_t *pid, float dt_min)
 {
-	pid->kp = kp;
-	pid->ki = ki;
-	pid->kd = kd;
-	pid->limit_min = limit_min;
-	pid->limit_max = limit_max;
-	pid->mode = mode;
 	pid->dt_min = dt_min;
-	pid->last_output = 0.0f;
+	pid->kp = 0.0f;
-	pid->sp = 0.0f;
+	pid->ki = 0.0f;
-	pid->error_previous = 0.0f;
+	pid->kd = 0.0f;
 	pid->integral = 0.0f;
+	pid->output_min = 0.0f;
+	pid->output_max = 0.0f;
+	pid->error_previous = 0.0f;
+	pid->last_output = 0.0f;
 }
 
-__EXPORT int thrust_pid_set_parameters(thrust_pid_t *pid, float kp, float ki, float kd, float limit_min, float limit_max)
+__EXPORT int thrust_pid_set_parameters(thrust_pid_t *pid, float kp, float ki, float kd, float output_min, float output_max)
 {
 	int ret = 0;
 
@@ -83,15 +83,15 @@ __EXPORT int thrust_pid_set_parameters(thrust_pid_t *pid, float kp, float ki, fl
 		ret = 1;
 	}
 
-	if (isfinite(limit_min)) {
+	if (isfinite(output_min)) {
-		pid->limit_min = limit_min;
+		pid->output_min = output_min;
 
 	}  else {
 		ret = 1;
 	}
 
-	if (isfinite(limit_max)) {
+	if (isfinite(output_max)) {
-		pid->limit_max = limit_max;
+		pid->output_max = output_max;
 
 	}  else {
 		ret = 1;
@@ -102,40 +102,18 @@ __EXPORT int thrust_pid_set_parameters(thrust_pid_t *pid, float kp, float ki, fl
 
 __EXPORT float thrust_pid_calculate(thrust_pid_t *pid, float sp, float val, float dt, float r22)
 {
-	/* Alternative integral component calculation
-	 *
-	 * start:
-	 * error = setpoint - current_value
-	 * integral = integral + (Ki * error * dt)
-	 * derivative = (error - previous_error) / dt
-	 * previous_error = error
-	 * output = (Kp * error) + integral + (Kd * derivative)
-	 * wait(dt)
-	 * goto start
-	 */
-
 	if (!isfinite(sp) || !isfinite(val) || !isfinite(dt)) {
 		return pid->last_output;
 	}
 
 	float i, d;
-	pid->sp = sp;
 
-	// Calculated current error value
+	/* error value */
-	float error = pid->sp - val;
+	float error = sp - val;
 
-	// Calculate or measured current error derivative
+	/* error derivative */
-	if (pid->mode == THRUST_PID_MODE_DERIVATIV_CALC) {
+	d = (-val - pid->error_previous) / fmaxf(dt, pid->dt_min);
-		d = (error - pid->error_previous) / fmaxf(dt, pid->dt_min);
+	pid->error_previous = -val;
-		pid->error_previous = error;
-
-	} else if (pid->mode == THRUST_PID_MODE_DERIVATIV_CALC_NO_SP) {
-		d = (-val - pid->error_previous) / fmaxf(dt, pid->dt_min);
-		pid->error_previous = -val;
-
-	} else {
-		d = 0.0f;
-	}
 
 	if (!isfinite(d)) {
 		d = 0.0f;
@@ -145,36 +123,41 @@ __EXPORT float thrust_pid_calculate(thrust_pid_t *pid, float sp, float val, floa
 	i = pid->integral + (pid->ki * error * dt);
 
 	/* attitude-thrust compensation
-	 * r22 is (2, 2) componet of rotation matrix for current attitude */
+	 * r22 is (2, 2) component of rotation matrix for current attitude */
 	float att_comp;
 
-	if (r22 > 0.8f)
+	if (r22 > COS_TILT_MAX) {
 		att_comp = 1.0f / r22;
-	else if (r22 > 0.0f)
-		att_comp = ((1.0f / 0.8f - 1.0f) / 0.8f) * r22 + 1.0f;
-	else
-		att_comp = 1.0f;
 
-	/* calculate output */
+	} else if (r22 > 0.0f) {
-	float output = ((error * pid->kp) + i + (d * pid->kd)) * att_comp;
+		att_comp = ((1.0f / COS_TILT_MAX - 1.0f) / COS_TILT_MAX) * r22 + 1.0f;
-
-	/* check for saturation */
-	if (output < pid->limit_min || output > pid->limit_max) {
-		/* saturated, recalculate output with old integral */
-		output = (error * pid->kp) + pid->integral + (d * pid->kd);
 
 	} else {
-		if (isfinite(i)) {
+		att_comp = 1.0f;
+	}
+
+	/* calculate PD output */
+	float output = ((error * pid->kp) + (d * pid->kd)) * att_comp;
+
+	/* check for saturation */
+	if (isfinite(i)) {
+		float i_comp = i * att_comp;
+		if ((output + i_comp) >= pid->output_min || (output + i_comp) <= pid->output_max) {
+			/* not saturated, use new integral value */
 			pid->integral = i;
 		}
 	}
 
-	if (isfinite(output)) {
+	/* add I component to output */
-		if (output > pid->limit_max) {
+	output += pid->integral * att_comp;
-			output = pid->limit_max;
 
-		} else if (output < pid->limit_min) {
+	/* limit output */
-			output = pid->limit_min;
+	if (isfinite(output)) {
+		if (output > pid->output_max) {
+			output = pid->output_max;
+
+		} else if (output < pid->output_min) {
+			output = pid->output_min;
 		}
 
 		pid->last_output = output;

src/modules/multirotor_pos_control/thrust_pid.h

@@ -47,27 +47,20 @@
 
 __BEGIN_DECLS
 
-/* PID_MODE_DERIVATIV_CALC calculates discrete derivative from previous error */
-#define THRUST_PID_MODE_DERIVATIV_CALC	0
-/* PID_MODE_DERIVATIV_CALC_NO_SP calculates discrete derivative from previous value, setpoint derivative is ignored */
-#define THRUST_PID_MODE_DERIVATIV_CALC_NO_SP	1
-
 typedef struct {
+	float dt_min;
 	float kp;
 	float ki;
 	float kd;
-	float sp;
 	float integral;
+	float output_min;
+	float output_max;
 	float error_previous;
 	float last_output;
-	float limit_min;
-	float limit_max;
-	float dt_min;
-	uint8_t mode;
 } thrust_pid_t;
 
-__EXPORT void thrust_pid_init(thrust_pid_t *pid, float kp, float ki, float kd, float limit_min, float limit_max, uint8_t mode, float dt_min);
+__EXPORT void thrust_pid_init(thrust_pid_t *pid, float dt_min);
-__EXPORT int thrust_pid_set_parameters(thrust_pid_t *pid, float kp, float ki, float kd, float limit_min, float limit_max);
+__EXPORT int thrust_pid_set_parameters(thrust_pid_t *pid, float kp, float ki, float kd, float output_min, float output_max);
 __EXPORT float thrust_pid_calculate(thrust_pid_t *pid, float sp, float val, float dt, float r22);
 __EXPORT void thrust_pid_set_integral(thrust_pid_t *pid, float i);