ardupilot/libraries/SITL/SIM_Rover.cpp

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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/>.
*/
/*
rover simulator class
*/
#include "SIM_Rover.h"
#include <string.h>
#include <stdio.h>
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namespace SITL {
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SimRover::SimRover(const char *frame_str) :
Aircraft(frame_str),
max_speed(20),
max_accel(10),
max_wheel_turn(35),
turning_circle(1.8),
skid_turn_rate(140), // degrees/sec
skid_steering(false)
{
skid_steering = strstr(frame_str, "skid") != nullptr;
if (skid_steering) {
printf("SKID Steering Rover Simulation Started\n");
// 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 SimRover::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));
}
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/*
return yaw rate in degrees/second given steering_angle and speed
*/
float SimRover::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 * d;
float t = c / speed;
float rate = 360.0f / t;
return rate;
}
/*
return lateral acceleration in m/s/s
*/
float SimRover::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 SimRover::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;
update_external_payload(input);
// update lat/lon/altitude
update_position();
time_advance();
// update magnetic field
update_mag_field_bf();
}
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} // namespace SITL