Rover: follow mode fixes and improvements

fix follow endless loop on enter
pass mavlink messages to AP_Follow
separate follow from guided
follow slows based on yaw error
check follow is enabled before entering follow mode
fix order in switch statement when converting from mode number to mode object
remove unused last_log_ms from follow mode

APMrover2/GCS_Mavlink.cpp

@@ -329,6 +329,13 @@ bool GCS_MAVLINK_Rover::try_send_message(enum ap_message id)
     return true;
 }
 
+void GCS_MAVLINK_Rover::packetReceived(const mavlink_status_t &status, mavlink_message_t &msg)
+{
+    // pass message to follow library
+    rover.g2.follow.handle_msg(msg);
+    GCS_MAVLINK::packetReceived(status, msg);
+}
+
 /*
   default stream rates to 1Hz
  */

APMrover2/GCS_Mavlink.h

@@ -40,6 +40,8 @@ private:
     void handle_change_alt_request(AP_Mission::Mission_Command &cmd) override;
     bool try_send_message(enum ap_message id) override;
 
+    void packetReceived(const mavlink_status_t &status, mavlink_message_t &msg) override;
+
     MAV_TYPE frame_type() const override;
     MAV_MODE base_mode() const override;
     uint32_t custom_mode() const override;

APMrover2/control_modes.cpp

@@ -21,6 +21,9 @@ Mode *Rover::mode_from_mode_num(const enum Mode::Number num)
     case Mode::Number::LOITER:
         ret = &mode_loiter;
         break;
+    case Mode::Number::FOLLOW:
+        ret = &mode_follow;
+        break;
     case Mode::Number::AUTO:
         ret = &mode_auto;
         break;
@@ -33,9 +36,6 @@ Mode *Rover::mode_from_mode_num(const enum Mode::Number num)
     case Mode::Number::GUIDED:
        ret = &mode_guided;
         break;
-    case Mode::Number::FOLLOW:
-        ret = &mode_follow;
-        break;
     case Mode::Number::INITIALISING:
         ret = &mode_initializing;
         break;

APMrover2/mode.h

@@ -467,7 +467,7 @@ public:
     bool attitude_stabilized() const override { return false; }
 };
 
-class ModeFollow : public ModeGuided
+class ModeFollow : public Mode
 {
 public:
 
@@ -480,5 +480,4 @@ public:
 protected:
 
     bool _enter() override;
-    uint32_t last_log_ms;   // system time of last time desired velocity was logging
 };

APMrover2/mode_follow.cpp

@@ -4,54 +4,70 @@
 // initialize follow mode
 bool ModeFollow::_enter()
 {
-    return ModeGuided::enter();
+    if (!g2.follow.enabled()) {
+        return false;
+    }
+
+    // initialise waypoint speed
+    set_desired_speed_to_default();
+
+    // initialise heading to current heading
+    _desired_yaw_cd = ahrs.yaw_sensor;
+    _yaw_error_cd = 0.0f;
+
+    return true;
 }
 
 void ModeFollow::update()
 {
-    // variables to be sent to velocity controller
-    Vector3f desired_velocity_neu_cms;
-    float yaw_cd = 0.0f;
+    // stop vehicle if no speed estimate
+    float speed;
+    if (!attitude_control.get_forward_speed(speed)) {
+        // no valid speed so stop
+        g2.motors.set_throttle(0.0f);
+        g2.motors.set_steering(0.0f);
+        return;
+    }
 
-    Vector3f dist_vec;  //vector to lead vehicle
+    Vector3f dist_vec;  // vector to lead vehicle
     Vector3f dist_vec_offs; // vector to lead vehicle + offset
     Vector3f vel_of_target; // velocity of lead vehicle
 
-    if (g2.follow.get_target_dist_and_vel_ned(dist_vec, dist_vec_offs, vel_of_target)) {
-
-        // convert dist_vec_offs to cm in NEU
-        const Vector3f dist_vec_offs_neu(dist_vec_offs.x * 100.f, dist_vec_offs.y * 100.0f, -dist_vec_offs.z * 100.0f);
-
-        // calculate desired velocity vector in cm/s in NEU
-        const float kp = g2.follow.get_pos_p().kP();
-        desired_velocity_neu_cms.x = (vel_of_target.x * 100.0f) + (dist_vec_offs_neu.x * kp);
-        desired_velocity_neu_cms.y = (vel_of_target.y * 100.0f) + (dist_vec_offs_neu.y * kp);
-
-        // scaled desired velocity to stay within horizontal speed limit
-        float desired_speed = safe_sqrt(sq(desired_velocity_neu_cms.x) + sq(desired_velocity_neu_cms.y));
-        if (!is_zero(desired_speed) && (desired_speed > _desired_speed)) {
-            const float scalar_xy = _desired_speed / desired_speed;
-            desired_velocity_neu_cms.x *= scalar_xy;
-            desired_velocity_neu_cms.y *= scalar_xy;
-            desired_speed = _desired_speed;
-        }
-
-        // unit vector towards target position (i.e. vector to lead vehicle + offset)
-        Vector3f dir_to_target_neu = dist_vec_offs_neu;
-        const float dir_to_target_neu_len = dir_to_target_neu.length();
-        if (!is_zero(dir_to_target_neu_len)) {
-            dir_to_target_neu /= dir_to_target_neu_len;
-        }
-
-        // calculate vehicle heading
-        const Vector3f dist_vec_xy(dist_vec_offs.x, dist_vec_offs.y, 0.0f);
-        if (dist_vec_xy.length() > 1.0f) {
-            yaw_cd = get_bearing_cd(Vector3f(), dist_vec_xy);
-        }
+    // if no target simply stop the vehicle
+    if (!g2.follow.get_target_dist_and_vel_ned(dist_vec, dist_vec_offs, vel_of_target)) {
+        _reached_destination = true;
+        stop_vehicle();
+        return;
     }
 
-    // re-use guided mode's heading and speed controller
-    ModeGuided::set_desired_heading_and_speed(yaw_cd, safe_sqrt(sq(desired_velocity_neu_cms.x) + sq(desired_velocity_neu_cms.y)));
+    // calculate desired velocity vector
+    Vector2f desired_velocity_ne;
+    const float kp = g2.follow.get_pos_p().kP();
+    desired_velocity_ne.x = vel_of_target.x + (dist_vec_offs.x * kp);
+    desired_velocity_ne.y = vel_of_target.y + (dist_vec_offs.y * kp);
 
-    ModeGuided::update();
+    // if desired velocity is zero stop vehicle
+    if (is_zero(desired_velocity_ne.x) && is_zero(desired_velocity_ne.y)) {
+        _reached_destination = true;
+        stop_vehicle();
+        return;
+    }
+
+    // we have not reached the target
+    _reached_destination = false;
+
+    // scale desired velocity to stay within horizontal speed limit
+    float desired_speed = safe_sqrt(sq(desired_velocity_ne.x) + sq(desired_velocity_ne.y));
+    if (!is_zero(desired_speed) && (desired_speed > _desired_speed)) {
+        const float scalar_xy = _desired_speed / desired_speed;
+        desired_velocity_ne *= scalar_xy;
+        desired_speed = _desired_speed;
+    }
+
+    // calculate vehicle heading
+    _desired_yaw_cd = wrap_180_cd(atan2f(desired_velocity_ne.y, desired_velocity_ne.x) * DEGX100);
+
+    // run steering and throttle controllers
+    calc_steering_to_heading(_desired_yaw_cd, desired_speed < 0);
+    calc_throttle(calc_reduced_speed_for_turn_or_distance(desired_speed), false, true);
 }