AC_AttControl_Multi: new multirotor specific attitude control class

libraries/AC_AttitudeControl/AC_AttitudeControl_Multi.cpp

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+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-
+
+#include "AC_AttitudeControl_Multi.h"
+#include <AP_HAL.h>
+#include <AP_Math.h>
+
+// returns a throttle including compensation for roll/pitch angle
+// throttle value should be 0 ~ 1000
+float AC_AttitudeControl_Multi::get_boosted_throttle(float throttle_in)
+{
+    // inverted_factor is 1 for tilt angles below 60 degrees
+    // reduces as a function of angle beyond 60 degrees
+    // becomes zero at 90 degrees
+    float min_throttle = _motors_multi.throttle_min();
+    float cos_tilt = _ahrs.cos_pitch() * _ahrs.cos_roll();
+    float inverted_factor = constrain_float(2.0f*cos_tilt, 0.0f, 1.0f);
+    float boost_factor = 1.0f/constrain_float(cos_tilt, 0.5f, 1.0f);
+
+    float throttle_out = (throttle_in-min_throttle)*inverted_factor*boost_factor + min_throttle;
+    _angle_boost = constrain_float(throttle_out - throttle_in,-32000,32000);
+    return throttle_out;
+}

libraries/AC_AttitudeControl/AC_AttitudeControl_Multi.h

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+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-
+
+/// @file    AC_AttitudeControl_Multi.h
+/// @brief   ArduCopter attitude control library
+
+#ifndef AC_AttitudeControl_Multi_H
+#define AC_AttitudeControl_Multi_H
+
+#include <AC_AttitudeControl.h>
+#include <AP_MotorsMulticopter.h>
+
+class AC_AttitudeControl_Multi : public AC_AttitudeControl {
+public:
+	AC_AttitudeControl_Multi(AP_AHRS &ahrs,
+                        const AP_Vehicle::MultiCopter &aparm,
+                        AP_MotorsMulticopter& motors,
+                        AC_P& pi_angle_roll, AC_P& pi_angle_pitch, AC_P& pi_angle_yaw,
+                        AC_PID& pid_rate_roll, AC_PID& pid_rate_pitch, AC_PID& pid_rate_yaw
+                        ) :
+        AC_AttitudeControl(ahrs, aparm, motors, pi_angle_roll, pi_angle_pitch, pi_angle_yaw, pid_rate_roll, pid_rate_pitch, pid_rate_yaw),
+        _motors_multi(motors)
+        {}
+
+	// empty destructor to suppress compiler warning
+	virtual ~AC_AttitudeControl_Multi() {}
+
+    // calculate total body frame throttle required to produce the given earth frame throttle
+    float get_boosted_throttle(float throttle_in);
+
+protected:
+
+    AP_MotorsMulticopter& _motors_multi;
+};
+
+#endif // AC_AttitudeControl_Multi_H