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SITL: add simple sailboat simulator

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This commit is contained in:
Randy Mackay 2018-09-24 16:16:23 +09:00
parent 833bc4e77d
commit 804305aa2b
2 changed files with 236 additions and 0 deletions
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libraries/SITL/SIM_Sailboat.cpp Normal file
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/*
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/>.
*/
/*
Sailboat simulator class
see explanation of lift and drag explained here: https://en.wikipedia.org/wiki/Forces_on_sails
To-Do: add heel handling by calculating lateral force from wind vs gravity force from heel to arrive at roll rate or acceleration
*/
#include "SIM_Sailboat.h"
#include <AP_Math/AP_Math.h>
#include <string.h>
#include <stdio.h>
namespace SITL {
Sailboat::Sailboat(const char *home_str, const char *frame_str) :
Aircraft(home_str, frame_str),
max_wheel_turn(35),
turning_circle(1.8)
{
}
// calculate the lift and drag as values from 0 to 1
// given an apparent wind speed in m/s and angle-of-attack in degrees
void Sailboat::calc_lift_and_drag(float wind_speed, float angle_of_attack_deg, float& lift, float& drag)
{
// check extremes
if (angle_of_attack_deg <= 0.0f) {
lift = lift_curve[0];
drag = drag_curve[0];
return;
}
if (angle_of_attack_deg >= 170.0f) {
lift = lift_curve[17];
drag = drag_curve[17];
return;
}
uint8_t index = constrain_int16(angle_of_attack_deg / 10, 0, 17);
float remainder = angle_of_attack_deg - (index * 10.0f);
lift = linear_interpolate(lift_curve[index], lift_curve[index+1], remainder, 0.0f, 10.0f);
drag = linear_interpolate(drag_curve[index], drag_curve[index+1], remainder, 0.0f, 10.0f);
// apply scaling by wind speed
lift *= wind_speed;
drag *= wind_speed;
}
/*
return turning circle (diameter) in meters for steering angle proportion in degrees
*/
float Sailboat::turn_circle(float steering)
{
if (fabsf(steering) < 1.0e-6) {
return 0;
}
return turning_circle * sinf(radians(max_wheel_turn)) / sinf(radians(steering*max_wheel_turn));
}
/*
return yaw rate in degrees/second given steering_angle and speed
*/
float Sailboat::calc_yaw_rate(float steering, float speed)
{
if (fabsf(steering) < 1.0e-6 or fabsf(speed) < 1.0e-6) {
return 0;
}
float d = turn_circle(steering);
float c = M_PI * d;
float t = c / speed;
float rate = 360.0f / t;
return rate;
}
/*
return lateral acceleration in m/s/s
*/
float Sailboat::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 sailboat simulation by one time step
*/
void Sailboat::update(const struct sitl_input &input)
{
// update wind
update_wind(input);
// in sailboats the steering controls the rudder, the throttle controls the main sail position
float steering = 2*((input.servos[0]-1000)/1000.0f - 0.5f);
// calculate mainsail angle from servo output 4, 0 to 90 degrees
float mainsail_angle_bf = constrain_float((input.servos[3]-1000)/1000.0f * 90.0f, 0.0f, 90.0f);
// calculate apparent wind in earth-frame (this is the direction the wind is coming from)
Vector3f wind_apparent_ef = wind_ef + velocity_ef;
const float wind_apparent_dir_ef = degrees(atan2f(wind_apparent_ef.y, wind_apparent_ef.x));
const float wind_apparent_speed = safe_sqrt(sq(wind_apparent_ef.x)+sq(wind_apparent_ef.y));
// calculate angle-of-attack from wind to mainsail
float aoa_deg = MAX(fabsf(wrap_180(wind_apparent_dir_ef - degrees(AP::ahrs().yaw))) - mainsail_angle_bf, 0);
// calculate Lift force (perpendicular to wind direction) and Drag force (parallel to wind direction)
float lift_wf, drag_wf;
calc_lift_and_drag(wind_apparent_speed, aoa_deg, lift_wf, drag_wf);
// rotate lift and drag from wind frame into body frame
const float wind_to_veh_rot_angle_deg = wrap_180(180 + wind_apparent_dir_ef - degrees(AP::ahrs().yaw));
const float sin_rot_rad = sinf(radians(wind_to_veh_rot_angle_deg));
const float cos_rot_rad = cosf(radians(wind_to_veh_rot_angle_deg));
const float force_fwd = fabsf((lift_wf * sin_rot_rad)) + (drag_wf * cos_rot_rad);
// 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);
gyro = Vector3f(0,0,radians(yaw_rate));
// update attitude
dcm.rotate(gyro * delta_time);
dcm.normalize();
// accel in body frame due acceleration from sail and deceleration from hull friction
accel_body = Vector3f((force_fwd * 1.0f) - (velocity_body.x * 0.5f), 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;
// update lat/lon/altitude
update_position();
time_advance();
// update magnetic field
update_mag_field_bf();
}
} // namespace SITL

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libraries/SITL/SIM_Sailboat.h Normal file
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/*
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/>.
*/
/*
sailboat simulator class
*/
#pragma once
#include "SIM_Aircraft.h"
namespace SITL {
/*
a sailboat simulator
*/
class Sailboat : public Aircraft {
public:
Sailboat(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 Sailboat(home_str, frame_str);
}
private:
void calc_lift_and_drag(float wind_speed, float angle_of_attack_deg, float& lift, float& drag);
float turn_circle(float steering);
float calc_yaw_rate(float steering, float speed);
float calc_lat_accel(float steering_angle, float speed);
float max_wheel_turn;
float turning_circle;
// 10 point curves for lift and drag. index is angle/10deg
// angle-of-attack 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170+
float lift_curve[18] = {0.00f, 0.00f, 0.80f, 1.00f, 0.95f, 0.75f, 0.60f, 0.40f, 0.20f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f};
float drag_curve[18] = {0.10f, 0.10f, 0.12f, 0.15f, 0.20f, 0.27f, 0.35f, 0.50f, 0.70f, 1.00f, 0.70f, 0.50f, 0.35f, 0.27f, 0.20f, 0.15f, 0.12f, 0.10f};
};
} // namespace SITL