SITL: converted rover simulator from python to C++

libraries/SITL/SIM_Aircraft.cpp

@@ -36,7 +36,6 @@ Aircraft::Aircraft(const char *home_str, const char *frame_str) :
     dcm(),
     gyro(),
     velocity_ef(),
-    velocity_body(),
     mass(0),
     accel_body(0, 0, -GRAVITY_MSS),
     time_now_us(0),
@@ -84,7 +83,6 @@ void Aircraft::update_position(void)
     location_update(location, bearing, distance);
 
     location.alt  = home.alt - position.z*100.0f;
-    velocity_body = dcm.transposed() * velocity_ef;
 
     time_now_us += frame_time_us;
     sync_frame_time();

libraries/SITL/SIM_Aircraft.h

@@ -62,7 +62,6 @@ protected:
     Matrix3f dcm;  // rotation matrix, APM conventions, from body to earth
     Vector3f gyro; // rad/s
     Vector3f velocity_ef; // m/s, earth frame
-    Vector3f velocity_body; // m/s, body frame
     Vector3f position; // meters, NED from origin
     float mass; // kg
     Vector3f accel_body; // m/s/s NED, body frame

libraries/SITL/SIM_Rover.cpp

@@ -0,0 +1,157 @@
+/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/*
+  rover simulator class
+*/
+
+#include "SIM_Rover.h"
+#include <stdio.h>
+#include <string.h>
+
+/*
+  constructor
+ */
+Rover::Rover(const char *home_str, const char *frame_str) :
+    Aircraft(home_str, frame_str),    
+    max_speed(20),
+    max_accel(30),
+    wheelbase(0.335),
+    wheeltrack(0.296),
+    max_wheel_turn(35),
+    turning_circle(1.8),
+    skid_turn_rate(140), // degrees/sec
+    skid_steering(false)
+{
+    skid_steering = strstr(frame_str, "skid") != NULL;
+
+    if (skid_steering) {
+        // these are taken from a 6V wild thumper with skid steering,
+        // with a sabertooth controller
+        max_accel = 14;
+        max_speed = 4;
+    }
+}
+
+
+
+/*
+  return turning circle (diameter) in meters for steering angle proportion in degrees
+*/
+float Rover::turn_circle(float steering)
+{
+    if (fabsf(steering) < 1.0e-6) {
+        return 0;
+    }
+    return turning_circle * sinf(radians(35)) / sinf(radians(steering*35));
+}
+
+/* 
+   return yaw rate in degrees/second given steering_angle and speed
+*/
+float Rover::calc_yaw_rate(float steering, float speed)
+{
+    if (skid_steering) {
+        return steering * skid_turn_rate;
+    }
+    if (fabsf(steering) < 1.0e-6 or fabsf(speed) < 1.0e-6) {
+        return 0;
+    }
+    float d = turn_circle(steering);
+    float c = M_PI_F * d;
+    float t = c / speed;
+    float rate = 360.0f / t;
+    return rate;
+}
+
+/*
+  return lateral acceleration in m/s/s
+*/
+float Rover::calc_lat_accel(float steering_angle, float speed)
+{
+    float yaw_rate = calc_yaw_rate(steering_angle, speed);
+    float accel = radians(yaw_rate) * speed;
+    return accel;
+}
+
+/*
+  update the rover simulation by one time step
+ */
+void Rover::update(const struct sitl_input &input)
+{
+    float steering, throttle;
+
+    // if in skid steering mode the steering and throttle values are used for motor1 and motor2
+    if (skid_steering) {
+        float motor1 = 2*((input.servos[0]-1000)/1000.0f - 0.5f);
+        float motor2 = 2*((input.servos[2]-1000)/1000.0f - 0.5f);
+        steering = motor1 - motor2;
+        throttle = 0.5*(motor1 + motor2);
+    } else {
+        steering = 2*((input.servos[0]-1000)/1000.0f - 0.5f);
+        throttle = 2*((input.servos[2]-1000)/1000.0f - 0.5f);
+    }
+
+    // how much time has passed?
+    float delta_time = frame_time_us * 1.0e-6f;
+
+    // speed in m/s in body frame
+    Vector3f velocity_body = dcm.transposed() * velocity_ef;
+
+    // speed along x axis, +ve is forward
+    float speed = velocity_body.x;
+
+    // yaw rate in degrees/s
+    float yaw_rate = calc_yaw_rate(steering, speed);
+
+    // target speed with current throttle
+    float target_speed = throttle * max_speed;
+
+    // linear acceleration in m/s/s - very crude model
+    float accel = max_accel * (target_speed - speed) / max_speed;
+
+    gyro = Vector3f(0,0,radians(yaw_rate));
+
+    // update attitude
+    dcm.rotate(gyro * delta_time);
+    dcm.normalize();
+
+    // accel in body frame due to motor
+    accel_body = Vector3f(accel, 0, 0);
+
+    // add in accel due to direction change
+    accel_body.y += radians(yaw_rate) * speed;
+
+    // now in earth frame
+    Vector3f accel_earth = dcm * accel_body;
+    accel_earth += Vector3f(0, 0, GRAVITY_MSS);
+
+    // we are on the ground, so our vertical accel is zero
+    accel_earth.z = 0;
+
+    // work out acceleration as seen by the accelerometers. It sees the kinematic
+    // acceleration (ie. real movement), plus gravity
+    accel_body = dcm.transposed() * (accel_earth + Vector3f(0, 0, -GRAVITY_MSS));
+
+    // new velocity vector
+    velocity_ef += accel_earth * delta_time;
+
+    // new position vector
+    position += velocity_ef * delta_time;
+    position.z = -home.alt*0.01f;
+
+    // update lat/lon/altitude
+    update_position();
+}

libraries/SITL/SIM_Rover.h

@@ -0,0 +1,55 @@
+/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/*
+  rover simulator class
+*/
+
+#ifndef _SIM_ROVER_H
+#define _SIM_ROVER_H
+
+#include "SIM_Aircraft.h"
+
+/*
+  a rover simulator
+ */
+class Rover : public Aircraft
+{
+public:
+    Rover(const char *home_str, const char *frame_str);
+
+    /* update model by one time step */
+    void update(const struct sitl_input &input);
+
+    /* static object creator */
+    static Aircraft *create(const char *home_str, const char *frame_str) { return new Rover(home_str, frame_str); }
+
+private:
+    float max_speed;
+    float max_accel;
+    float wheelbase;
+    float wheeltrack;
+    float max_wheel_turn;
+    float turning_circle;
+    float skid_turn_rate;
+    bool skid_steering;
+
+    float turn_circle(float steering);
+    float calc_yaw_rate(float steering, float speed);
+    float calc_lat_accel(float steering_angle, float speed);
+};
+
+
+#endif // _SIM_ROVER_H