ardupilot/libraries/SITL/SIM_Motor.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/>.
*/
/*
simple electric motor simulator class
*/
#include "SIM_Motor.h"
#include <AP_Motors/AP_Motors.h>
using namespace SITL;
// calculate rotational accel and thrust for a motor
void Motor::calculate_forces(const struct sitl_input &input,
uint8_t motor_offset,
Vector3f &rot_accel,
Vector3f &thrust,
const Vector3f &velocity_air_bf,
float air_density,
float velocity_max,
float effective_prop_area,
float voltage)
{
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// fudge factors
const float yaw_scale = radians(400);
const float pwm = input.servos[motor_offset+servo];
float command = pwm_to_command(pwm);
float voltage_scale = voltage / voltage_max;
if (voltage_scale < 0.1) {
// battery is dead
rot_accel.zero();
thrust.zero();
current = 0;
return;
}
// apply slew limiter to command
uint64_t now_us = AP_HAL::micros64();
if (last_calc_us != 0 && slew_max > 0) {
float dt = (now_us - last_calc_us)*1.0e-6;
float slew_max_change = slew_max * dt;
command = constrain_float(command, last_command-slew_max_change, last_command+slew_max_change);
}
last_calc_us = now_us;
last_command = command;
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// the yaw torque of the motor
Vector3f rotor_torque(0, 0, yaw_factor * command * yaw_scale * voltage_scale);
// calculate velocity into prop, clipping at zero, assumes zero roll/pitch
float velocity_in = MAX(0, -velocity_air_bf.z);
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// get thrust for untilted motor
float motor_thrust = calc_thrust(command, air_density, effective_prop_area, velocity_in, velocity_max * voltage_scale);
// thrust in NED
thrust = {0, 0, -motor_thrust};
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// define the arm position relative to center of mass
Vector3f arm(cosf(radians(angle)), sinf(radians(angle)), 0);
arm *= diagonal_size;
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// work out roll and pitch of motor relative to it pointing straight up
float roll = 0, pitch = 0;
uint64_t now = AP_HAL::micros64();
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// possibly roll and/or pitch the motor
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if (roll_servo >= 0) {
uint16_t servoval = update_servo(input.servos[roll_servo+motor_offset], now, last_roll_value);
if (roll_min < roll_max) {
roll = constrain_float(roll_min + (servoval-1000)*0.001*(roll_max-roll_min), roll_min, roll_max);
} else {
roll = constrain_float(roll_max + (2000-servoval)*0.001*(roll_min-roll_max), roll_max, roll_min);
}
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}
if (pitch_servo >= 0) {
uint16_t servoval = update_servo(input.servos[pitch_servo+motor_offset], now, last_pitch_value);
if (pitch_min < pitch_max) {
pitch = constrain_float(pitch_min + (servoval-1000)*0.001*(pitch_max-pitch_min), pitch_min, pitch_max);
} else {
pitch = constrain_float(pitch_max + (2000-servoval)*0.001*(pitch_min-pitch_max), pitch_max, pitch_min);
}
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}
last_change_usec = now;
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// possibly rotate the thrust vector and the rotor torque
if (!is_zero(roll) || !is_zero(pitch)) {
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Matrix3f rotation;
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rotation.from_euler(radians(roll), radians(pitch), 0);
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thrust = rotation * thrust;
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rotor_torque = rotation * rotor_torque;
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}
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// calculate torque in newton-meters
Vector3f torque = (arm % thrust) + rotor_torque;
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// calculate total rotational acceleration
rot_accel.x = torque.x / moment_of_inertia.x;
rot_accel.y = torque.y / moment_of_inertia.y;
rot_accel.z = torque.z / moment_of_inertia.z;
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// calculate current
float power = power_factor * fabsf(motor_thrust);
current = power / MAX(voltage, 0.1);
}
/*
update and return current value of a servo. Calculated as 1000..2000
*/
uint16_t Motor::update_servo(uint16_t demand, uint64_t time_usec, float &last_value)
{
if (servo_rate <= 0) {
return demand;
}
if (servo_type == SERVO_RETRACT) {
// handle retract servos
if (demand > 1700) {
demand = 2000;
} else if (demand < 1300) {
demand = 1000;
} else {
demand = last_value;
}
}
demand = constrain_int16(demand, 1000, 2000);
float dt = (time_usec - last_change_usec) * 1.0e-6f;
// assume servo moves through 90 degrees over 1000 to 2000
float max_change = 1000 * (dt / servo_rate) * 60.0f / 90.0f;
last_value = constrain_float(demand, last_value-max_change, last_value+max_change);
return uint16_t(last_value+0.5);
}
// calculate current and voltage
float Motor::get_current(void) const
{
return current;
}
// setup PWM ranges for this motor
void Motor::setup_params(uint16_t _pwm_min, uint16_t _pwm_max, float _spin_min, float _spin_max, float _expo, float _slew_max,
float _vehicle_mass, float _diagonal_size, float _power_factor, float _voltage_max)
{
mot_pwm_min = _pwm_min;
mot_pwm_max = _pwm_max;
mot_spin_min = _spin_min;
mot_spin_max = _spin_max;
mot_expo = _expo;
slew_max = _slew_max;
vehicle_mass = _vehicle_mass;
diagonal_size = _diagonal_size;
power_factor = _power_factor;
voltage_max = _voltage_max;
// assume 50% of mass on ring around center
moment_of_inertia.x = vehicle_mass * 0.25 * sq(diagonal_size*0.5);
moment_of_inertia.y = moment_of_inertia.x;
moment_of_inertia.z = vehicle_mass * 0.5 * sq(diagonal_size*0.5);
}
/*
convert a PWM value to a command value from 0 to 1
*/
float Motor::pwm_to_command(float pwm) const
{
const float pwm_thrust_max = mot_pwm_min + mot_spin_max * (mot_pwm_max - mot_pwm_min);
const float pwm_thrust_min = mot_pwm_min + mot_spin_min * (mot_pwm_max - mot_pwm_min);
const float pwm_thrust_range = pwm_thrust_max - pwm_thrust_min;
return constrain_float((pwm-pwm_thrust_min)/pwm_thrust_range, 0, 1);
}
/*
calculate thrust given a command value
*/
float Motor::calc_thrust(float command, float air_density, float effective_prop_area, float velocity_in, float velocity_max) const
{
float velocity_out = velocity_max * sqrtf((1-mot_expo)*command + mot_expo*sq(command));
float ret = 0.5 * air_density * effective_prop_area * (sq(velocity_out) - sq(velocity_in));
#if 0
if (command > 0) {
::printf("air_density=%f effective_prop_area=%f velocity_in=%f velocity_max=%f\n",
air_density, effective_prop_area, velocity_in, velocity_max);
::printf("calc_thrust %.3f %.3f\n", command, ret);
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}
#endif
return ret;
}