ardupilot/libraries/SITL/SIM_Helicopter.cpp

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/// -*- 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/>.
*/
/*
helicopter simulator class
*/
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#include <AP_HAL.h>
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
#include "SIM_Helicopter.h"
#include <stdio.h>
/*
constructor
*/
Helicopter::Helicopter(const char *home_str, const char *frame_str) :
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Aircraft(home_str, frame_str),
terminal_rotation_rate(4*radians(360.0)),
hover_throttle(0.65f),
terminal_velocity(40.0f),
hover_lean(8.0f),
yaw_zero(0.1f),
rotor_rot_accel(radians(20)),
roll_rate_max(radians(1400)),
pitch_rate_max(radians(1400)),
yaw_rate_max(radians(1400)),
rsc_setpoint(0.8f)
{
mass = 2.13f;
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/*
scaling from motor power to Newtons. Allows the copter
to hover against gravity when the motor is at hover_throttle
*/
thrust_scale = (mass * GRAVITY_MSS) / hover_throttle;
// calculate lateral thrust ratio for tail rotor
tail_thrust_scale = sinf(radians(hover_lean)) * thrust_scale / yaw_zero;
frame_height = 0.1;
}
/*
update the helicopter simulation by one time step
*/
void Helicopter::update(const struct sitl_input &input)
{
float swash1 = (input.servos[0]-1000) / 1000.0f;
float swash2 = (input.servos[1]-1000) / 1000.0f;
float swash3 = (input.servos[2]-1000) / 1000.0f;
float tail_rotor = (input.servos[3]-1000) / 1000.0f;
float rsc = (input.servos[7]-1000) / 1000.0f;
// how much time has passed?
float delta_time = frame_time_us * 1.0e-6f;
float thrust = (rsc/rsc_setpoint)*(swash1+swash2+swash3)/3.0f;
// very simplistic mapping to body euler rates
float roll_rate = swash1 - swash2;
float pitch_rate = (swash1 + swash2)/2.0f - swash3;
float yaw_rate = tail_rotor - 0.5f;
float rsc_scale = rsc/rsc_setpoint;
roll_rate *= rsc_scale;
pitch_rate *= rsc_scale;
yaw_rate *= rsc_scale;
// rotational acceleration, in rad/s/s, in body frame
Vector3f rot_accel;
rot_accel.x = roll_rate * roll_rate_max;
rot_accel.y = pitch_rate * pitch_rate_max;
rot_accel.z = yaw_rate * yaw_rate_max;
// rotational air resistance
rot_accel.x -= gyro.x * radians(5000.0) / terminal_rotation_rate;
rot_accel.y -= gyro.y * radians(5000.0) / terminal_rotation_rate;
rot_accel.z -= gyro.z * radians(400.0) / terminal_rotation_rate;
// torque effect on tail
rot_accel.z += (rsc_scale+thrust) * rotor_rot_accel;
// update rotational rates in body frame
gyro += rot_accel * delta_time;
// update attitude
dcm.rotate(gyro * delta_time);
dcm.normalize();
// air resistance
Vector3f air_resistance = -velocity_ef * (GRAVITY_MSS/terminal_velocity);
// scale thrust to newtons
thrust *= thrust_scale;
accel_body = Vector3f(0, yaw_rate * rsc_scale * tail_thrust_scale, -thrust / mass);
Vector3f accel_earth = dcm * accel_body;
accel_earth += Vector3f(0, 0, GRAVITY_MSS);
accel_earth += air_resistance;
// if we're on the ground, then our vertical acceleration is limited
// to zero. This effectively adds the force of the ground on the aircraft
if (on_ground(position) && accel_earth.z > 0) {
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));
// add some noise
add_noise(thrust / thrust_scale);
// new velocity vector
velocity_ef += accel_earth * delta_time;
// new position vector
Vector3f old_position = position;
position += velocity_ef * delta_time;
// constrain height to the ground
if (on_ground(position)) {
if (!on_ground(old_position)) {
printf("Hit ground at %f m/s\n", velocity_ef.z);
velocity_ef.zero();
// zero roll/pitch, but keep yaw
float r, p, y;
dcm.to_euler(&r, &p, &y);
dcm.from_euler(0, 0, y);
position.z = -(ground_level + frame_height - home.alt*0.01f);
}
}
// update lat/lon/altitude
update_position();
}
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#endif // CONFIG_HAL_BOARD