ardupilot/libraries/AP_Motors/AP_MotorsHeli_RSC.cpp

/*
   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/>.
 */

#include <stdlib.h>
#include <AP_HAL/AP_HAL.h>

#include "AP_MotorsHeli_RSC.h"

extern const AP_HAL::HAL& hal;

const AP_Param::GroupInfo AP_MotorsHeli_RSC::var_info[] = {

    // @Param: SETPOINT
    // @DisplayName: External Motor Governor Setpoint
    // @Description: Throttle (HeliRSC Servo) output in percent to the external motor governor when motor interlock enabled (throttle hold off).
    // @Range: 0 100
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("SETPOINT", 1, AP_MotorsHeli_RSC, _rsc_setpoint, AP_MOTORS_HELI_RSC_SETPOINT),

    // @Param: MODE
    // @DisplayName: Rotor Speed Control Mode
    // @Description: Selects the type of rotor speed control used to determine throttle output to the HeliRSC servo channel when motor interlock is enabled (throttle hold off). RC Passthrough sends the input from the RC Motor Interlock channel as throttle output.  External Gov SetPoint sends the RSC SetPoint parameter value as throttle output.  Throttle Curve uses the 5 point throttle curve to determine throttle output based on the collective output.  Governor is ArduCopter's built-in governor that uses the throttle curve for a feed forward throttle command to determine throttle output.
    // @Values: 1:RC Passthrough, 2:External Gov SetPoint, 3:Throttle Curve, 4:Governor
    // @User: Standard
    AP_GROUPINFO("MODE", 2, AP_MotorsHeli_RSC, _rsc_mode, (int8_t)ROTOR_CONTROL_MODE_SPEED_PASSTHROUGH),

    // @Param: RAMP_TIME
    // @DisplayName: Throttle Ramp Time
    // @Description: Time in seconds for throttle output (HeliRSC servo) to ramp from ground idle (RSC_IDLE) to flight idle throttle setting when motor interlock is enabled (throttle hold off).
    // @Range: 0 60
    // @Units: s
    // @User: Standard
    AP_GROUPINFO("RAMP_TIME", 3, AP_MotorsHeli_RSC, _ramp_time, AP_MOTORS_HELI_RSC_RAMP_TIME),

    // @Param: RUNUP_TIME
    // @DisplayName: Rotor Runup Time
    // @Description: Actual time in seconds for the main rotor to reach full speed after motor interlock is enabled (throttle hold off). Must be at least one second longer than the Throttle Ramp Time that is set with RSC_RAMP_TIME.
    // @Range: 0 60
    // @Units: s
    // @User: Standard
    AP_GROUPINFO("RUNUP_TIME", 4, AP_MotorsHeli_RSC, _runup_time, AP_MOTORS_HELI_RSC_RUNUP_TIME),

    // @Param: CRITICAL
    // @DisplayName: Critical Rotor Speed
    // @Description: Percentage of normal rotor speed where flight is no longer possible. However currently the rotor runup/rundown is estimated using the RSC_RUNUP_TIME parameter.   Estimated rotor speed increases/decreases between 0 (rotor stopped) to 1 (rotor at normal speed) in the RSC_RUNUP_TIME in seconds. This parameter should be set so that the estimated rotor speed goes below critical in approximately 3 seconds.  So if you had a 10 second runup time then set RSC_CRITICAL to 70%.
    // @Range: 0 100
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("CRITICAL", 5, AP_MotorsHeli_RSC, _critical_speed, AP_MOTORS_HELI_RSC_CRITICAL),

    // @Param: IDLE
    // @DisplayName: Throttle Output at Idle
    // @Description: Throttle output (HeliRSC Servo) in percent while armed but motor interlock is disabled (throttle hold on). FOR COMBUSTION ENGINES. Sets the engine ground idle throttle percentage with clutch disengaged. This must be set to zero for electric helicopters under most situations. If the ESC has an autorotation window this can be set to keep the autorotation window open in the ESC. Consult the operating manual for your ESC to set it properly for this purpose
    // @Range: 0 50
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("IDLE", 6, AP_MotorsHeli_RSC, _idle_output, AP_MOTORS_HELI_RSC_IDLE_DEFAULT),

    // @Param: SLEWRATE
    // @DisplayName: Throttle Slew Rate
    // @Description: This controls the maximum rate at which the throttle output (HeliRSC servo) can change, as a percentage per second. A value of 100 means the throttle can change over its full range in one second. A value of zero gives unlimited slew rate.
    // @Range: 0 500
    // @Increment: 10
    // @User: Standard
    AP_GROUPINFO("SLEWRATE", 7, AP_MotorsHeli_RSC, _power_slewrate, 0),

    // @Param: THRCRV_0
    // @DisplayName: Throttle Curve at 0% Coll
    // @Description: Sets the throttle output (HeliRSC servo) in percent for the throttle curve at the minimum collective pitch position. The 0 percent collective is defined by H_COL_MIN. Example: if the setup has -2 degree to +10 degree collective pitch setup, this setting would correspond to -2 degree of pitch.
    // @Range: 0 100
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("THRCRV_0", 8, AP_MotorsHeli_RSC, _thrcrv[0], AP_MOTORS_HELI_RSC_THRCRV_0_DEFAULT),

    // @Param: THRCRV_25
    // @DisplayName: Throttle Curve at 25% Coll
    // @Description: Sets the throttle output (HeliRSC servo) in percent for the throttle curve at 25% of full collective travel where he 0 percent collective is defined by H_COL_MIN and 100 percent collective is defined by H_COL_MAX.  Example: if the setup has -2 degree to +10 degree collective pitch setup, the total range is 12 degrees. 25% of 12 degrees is 3 degrees, so this setting would correspond to +1 degree of pitch.
    // @Range: 0 100
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("THRCRV_25", 9, AP_MotorsHeli_RSC, _thrcrv[1], AP_MOTORS_HELI_RSC_THRCRV_25_DEFAULT),

    // @Param: THRCRV_50
    // @DisplayName: Throttle Curve at 50% Coll
    // @Description: Sets the throttle output (HeliRSC servo) in percent for the throttle curve at 50% of full collective travel where he 0 percent collective is defined by H_COL_MIN and 100 percent collective is defined by H_COL_MAX.  Example: if the setup has -2 degree to +10 degree collective pitch setup, the total range is 12 degrees. 50% of 12 degrees is 6 degrees, so this setting would correspond to +4 degree of pitch.
    // @Range: 0 100
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("THRCRV_50", 10, AP_MotorsHeli_RSC, _thrcrv[2], AP_MOTORS_HELI_RSC_THRCRV_50_DEFAULT),

    // @Param: THRCRV_75
    // @DisplayName: Throttle Curve at 75% Coll
    // @Description: Sets the throttle output (HeliRSC servo) in percent for the throttle curve at 75% of full collective travel where he 0 percent collective is defined by H_COL_MIN and 100 percent collective is defined by H_COL_MAX.  Example: if the setup has -2 degree to +10 degree collective pitch setup, the total range is 12 degrees. 75% of 12 degrees is 9 degrees, so this setting would correspond to +7 degree of pitch.
    // @Range: 0 100
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("THRCRV_75", 11, AP_MotorsHeli_RSC, _thrcrv[3], AP_MOTORS_HELI_RSC_THRCRV_75_DEFAULT),

    // @Param: THRCRV_100
    // @DisplayName: Throttle Curve at 100% Coll
    // @Description: Sets the throttle output (HeliRSC servo) in percent for the throttle curve at the minimum collective pitch position. The 100 percent collective is defined by H_COL_MAX.  Example: if the setup has -2 degree to +10 degree collective pitch setup, this setting would correspond to +10 degree of pitch.
    // @Range: 0 100
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("THRCRV_100", 12, AP_MotorsHeli_RSC, _thrcrv[4], AP_MOTORS_HELI_RSC_THRCRV_100_DEFAULT),

    // @Param: GOV_SETPNT
    // @DisplayName: Rotor Governor Setpoint
    // @Description: Main rotor rpm setting that governor maintains when engaged.  Set to the rotor rpm your helicopter runs in flight. When a speed sensor is installed the rotor governor maintains this speed. For governor operation this should be set 10 rpm higher than the actual desired headspeed to allow for governor droop
    // @Range: 800 3500
    // @Units: RPM
    // @Increment: 10
    // @User: Standard
    AP_GROUPINFO("GOV_SETPNT", 13, AP_MotorsHeli_RSC, _governor_reference, AP_MOTORS_HELI_RSC_GOVERNOR_SETPNT_DEFAULT),

    // @Param: GOV_DISGAG
    // @DisplayName: Governor Disengage Throttle
    // @Description: Percentage of throttle where the governor will disengage to allow return to flight idle power. Typically should be set to the same value as flight idle throttle (the very lowest throttle setting on the throttle curve). The governor disengage can be disabled by setting this value to zero and using the pull-down from the governor TCGAIN to reduce power to flight idle with the collective at it's lowest throttle setting on the throttle curve.
    // @Range: 0 50
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("GOV_DISGAG", 14, AP_MotorsHeli_RSC, _governor_disengage, AP_MOTORS_HELI_RSC_GOVERNOR_DISENGAGE_DEFAULT),

    // @Param: GOV_DROOP
    // @DisplayName: Governor Droop Response
    // @Description: Governor droop response under load, normal settings of 0-100%. Higher value is quicker response but may cause surging. Setting to zero disables the governor. Adjust this to be as aggressive as possible without getting surging or over-run on headspeed when the governor engages. Setting over 100% is allowable for some two-stage turbine engines to provide scheduling of the gas generator for proper torque response of the N2 spool
    // @Range: 0 150
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("GOV_DROOP", 15, AP_MotorsHeli_RSC, _governor_droop_response, AP_MOTORS_HELI_RSC_GOVERNOR_DROOP_DEFAULT),

    // @Param: GOV_TCGAIN
    // @DisplayName: Governor Throttle Curve Gain
    // @Description: Percentage of throttle curve gain in governor output. This provides a type of feedforward response to sudden loading or unloading of the engine. If headspeed drops excessively during sudden heavy load, increase the throttle curve gain. If the governor runs with excessive droop more than 15 rpm lower than the speed setting, increase this setting until the governor runs at 8-10 rpm droop from the speed setting. The throttle curve must be properly tuned to fly the helicopter without the governor for this setting to work properly.
    // @Range: 50 100
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("GOV_TCGAIN", 16, AP_MotorsHeli_RSC, _governor_tcgain, AP_MOTORS_HELI_RSC_GOVERNOR_TCGAIN_DEFAULT),
    
    // @Param: GOV_RANGE
    // @DisplayName: Governor Operational Range
    // @Description: RPM range +/- governor rpm reference setting where governor is operational. If speed sensor fails or rpm falls outside of this range, the governor will disengage and return to throttle curve. Recommended range is 100
    // @Range: 50 200
    // @Units: RPM
    // @Increment: 10
    // @User: Standard
    AP_GROUPINFO("GOV_RANGE", 17, AP_MotorsHeli_RSC, _governor_range, AP_MOTORS_HELI_RSC_GOVERNOR_RANGE_DEFAULT),

#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
    // @Param: AROT_PCT
    // @DisplayName: Autorotation Throttle Percentage for External Governor
    // @Description: The throttle percentage sent to external governors, signaling to enable fast spool-up, when bailing out of an autorotation.  Set 0 to disable. If also using a tail rotor of type DDVP with external governor then this value must lie within the autorotation window of both governors.
    // @Range: 0 40
    // @Units: %
    // @Increment: 1
    // @User: Standard
    AP_GROUPINFO("AROT_PCT", 18, AP_MotorsHeli_RSC, _ext_gov_arot_pct, 0),
#endif

    AP_GROUPEND
};

// init_servo - servo initialization on start-up
void AP_MotorsHeli_RSC::init_servo()
{
    // setup RSC on specified channel by default
    SRV_Channels::set_aux_channel_default(_aux_fn, _default_channel);

    // set servo range 
    SRV_Channels::set_range(SRV_Channels::get_motor_function(_aux_fn), 1000);

}

// set_power_output_range
// TODO: Look at possibly calling this at a slower rate.  Doesn't need to be called every cycle.
void AP_MotorsHeli_RSC::set_throttle_curve()
{
    float thrcrv[5];
    // Ensure user inputs are within parameter limits
    // Scale throttle curve parameters
    for (uint8_t i = 0; i < 5; i++) {
        thrcrv[i] = constrain_float(_thrcrv[i] * 0.01f, 0.0f, 1.0f);
    }
    // Calculate the spline polynomials for the throttle curve
    splinterp5(thrcrv,_thrcrv_poly);
}

// output - update value to send to ESC/Servo
void AP_MotorsHeli_RSC::output(RotorControlState state)
{
    float dt;
    uint64_t now = AP_HAL::micros64();
    float last_control_output = _control_output;

    if (_last_update_us == 0) {
        _last_update_us = now;
        dt = 0.001f;
    } else {
        dt = 1.0e-6f * (now - _last_update_us);
        _last_update_us = now;
    }

    switch (state){
        case ROTOR_CONTROL_STOP:
            // set rotor ramp to decrease speed to zero, this happens instantly inside update_rotor_ramp()
            update_rotor_ramp(0.0f, dt);

            // control output forced to zero
            _control_output = 0.0f;
            break;

        case ROTOR_CONTROL_IDLE:
            // set rotor ramp to decrease speed to zero
            update_rotor_ramp(0.0f, dt);

            if (_in_autorotation) {
                // if in autorotation and using an external governor, set the output to tell the governor to use bailout ramp
                _control_output = constrain_float( _rsc_arot_bailout_pct/100.0f , 0.0f, 0.4f);
            } else {
                // set rotor control speed to idle speed parameter, this happens instantly and ignores ramping
                _control_output = get_idle_output();
            }
            break;

        case ROTOR_CONTROL_ACTIVE:
            // set main rotor ramp to increase to full speed
            update_rotor_ramp(1.0f, dt);

            if ((_control_mode == ROTOR_CONTROL_MODE_SPEED_PASSTHROUGH) || (_control_mode == ROTOR_CONTROL_MODE_SPEED_SETPOINT)) {
                // set control rotor speed to ramp slewed value between idle and desired speed
                _control_output = get_idle_output() + (_rotor_ramp_output * (_desired_speed - get_idle_output()));
            } else if (_control_mode == ROTOR_CONTROL_MODE_OPEN_LOOP_POWER_OUTPUT) {
                // throttle output from throttle curve based on collective position
                float desired_throttle = calculate_desired_throttle(_collective_in);
                _control_output = get_idle_output() + (_rotor_ramp_output * (desired_throttle - get_idle_output()));
            } else if (_control_mode == ROTOR_CONTROL_MODE_CLOSED_LOOP_POWER_OUTPUT) {
                // governor provides two modes of throttle control - governor engaged
                // or throttle curve if governor is out of range or sensor failed
            	float desired_throttle = calculate_desired_throttle(_collective_in);
            	// governor is active if within user-set range from reference speed
                if ((_rotor_rpm >= ((float)_governor_reference - _governor_range)) && (_rotor_rpm <= ((float)_governor_reference + _governor_range))) {
            	    float governor_droop = constrain_float((float)_governor_reference - _rotor_rpm,0.0f,_governor_range);
            	    // if rpm has not reached 40% of the operational range from reference speed, governor
            	    // remains in pre-engage status, no reference speed compensation due to droop
            	    // this provides a soft-start function that engages the governor less aggressively
            	    if (_governor_engage && _rotor_rpm < ((float)_governor_reference - (_governor_range * 0.4f))) {
                        _governor_output = ((_rotor_rpm - (float)_governor_reference) * desired_throttle) * get_governor_droop_response() * -0.01f;
                    } else {
            	        // normal flight status, governor fully engaged with reference speed compensation for droop
            	        _governor_engage = true;
                        _governor_output = ((_rotor_rpm - ((float)_governor_reference + governor_droop)) * desired_throttle) * get_governor_droop_response() * -0.01f;
                    }
                    // check for governor disengage for return to flight idle power
                    if (desired_throttle <= get_governor_disengage()) {
                        _governor_output = 0.0f;
                        _governor_engage = false;
                    }
                    // throttle output with governor on is constrained from minimum called for from throttle curve
                    // to maximum WOT. This prevents outliers on rpm signal from closing the throttle in flight due
                    // to rpm sensor failure or bad signal quality
            	    _control_output = constrain_float(get_idle_output() + (_rotor_ramp_output * (((desired_throttle * get_governor_tcgain()) + _governor_output) - get_idle_output())), get_idle_output() + (_rotor_ramp_output * ((desired_throttle * get_governor_tcgain())) - get_idle_output()), 1.0f);
            	} else {
            	    // hold governor output at zero, engage status is false and use the throttle curve
            	    // this is failover for in-flight failure of the speed sensor
            	    _governor_output = 0.0f;
            	    _governor_engage = false;
                    _control_output = get_idle_output() + (_rotor_ramp_output * (desired_throttle - get_idle_output()));
                }
            }
            break;
    }

    // update rotor speed run-up estimate
    update_rotor_runup(dt);

    if (_power_slewrate > 0) {
        // implement slew rate for throttle
        float max_delta = dt * _power_slewrate * 0.01f;
        _control_output = constrain_float(_control_output, last_control_output-max_delta, last_control_output+max_delta);
    }

    // output to rsc servo
    write_rsc(_control_output);
}

// update_rotor_ramp - slews rotor output scalar between 0 and 1, outputs float scalar to _rotor_ramp_output
void AP_MotorsHeli_RSC::update_rotor_ramp(float rotor_ramp_input, float dt)
{
    int8_t ramp_time;
    // sanity check ramp time and enable bailout if set
    if (_use_bailout_ramp || _ramp_time <= 0) {
        ramp_time = 1;
    } else {
        ramp_time = _ramp_time;
    }

    // ramp output upwards towards target
    if (_rotor_ramp_output < rotor_ramp_input) {
        // allow control output to jump to estimated speed
        if (_rotor_ramp_output < _rotor_runup_output) {
            _rotor_ramp_output = _rotor_runup_output;
        }
        // ramp up slowly to target
        _rotor_ramp_output += (dt / ramp_time);
        if (_rotor_ramp_output > rotor_ramp_input) {
            _rotor_ramp_output = rotor_ramp_input;
        }
    }else{
        // ramping down happens instantly
        _rotor_ramp_output = rotor_ramp_input;
    }
}

// update_rotor_runup - function to slew rotor runup scalar, outputs float scalar to _rotor_runup_ouptut
void AP_MotorsHeli_RSC::update_rotor_runup(float dt)
{
    int8_t runup_time = _runup_time;
    // sanity check runup time
    runup_time = MAX(_ramp_time+1,runup_time);

    // adjust rotor runup when bailing out
    if (_use_bailout_ramp) {
        // maintain same delta as set in parameters
        runup_time = _runup_time-_ramp_time+1;
    }

    // protect against divide by zero
    runup_time = MAX(1,runup_time);

    // ramp speed estimate towards control out
    float runup_increment = dt / runup_time;
    if (_rotor_runup_output < _rotor_ramp_output) {
        _rotor_runup_output += runup_increment;
        if (_rotor_runup_output > _rotor_ramp_output) {
            _rotor_runup_output = _rotor_ramp_output;
        }
    }else{
        _rotor_runup_output -= runup_increment;
        if (_rotor_runup_output < _rotor_ramp_output) {
            _rotor_runup_output = _rotor_ramp_output;
        }
    }

    // update run-up complete flag

    // if control mode is disabled, then run-up complete always returns true
    if ( _control_mode == ROTOR_CONTROL_MODE_DISABLED ){
        _runup_complete = true;
        return;
    }

    // if rotor ramp and runup are both at full speed, then run-up has been completed
    if (!_runup_complete && (_rotor_ramp_output >= 1.0f) && (_rotor_runup_output >= 1.0f)) {
        _runup_complete = true;
    }
    // if rotor speed is less than critical speed, then run-up is not complete
    // this will prevent the case where the target rotor speed is less than critical speed
    if (_runup_complete && (get_rotor_speed() <= get_critical_speed())) {
        _runup_complete = false;
    }
    // if rotor estimated speed is zero, then spooldown has been completed
    if (get_rotor_speed() <= 0.0f) { _spooldown_complete = true; } else { _spooldown_complete = false; }
}

// get_rotor_speed - gets rotor speed either as an estimate, or (ToDO) a measured value
float AP_MotorsHeli_RSC::get_rotor_speed() const
{
    // if no actual measured rotor speed is available, estimate speed based on rotor runup scalar.
    return _rotor_runup_output;
}

// write_rsc - outputs pwm onto output rsc channel
// servo_out parameter is of the range 0 ~ 1
void AP_MotorsHeli_RSC::write_rsc(float servo_out)
{
    if (_control_mode == ROTOR_CONTROL_MODE_DISABLED){
        // do not do servo output to avoid conflicting with other output on the channel
        // ToDo: We should probably use RC_Channel_Aux to avoid this problem
        return;
    } else {
        SRV_Channels::set_output_scaled(_aux_fn, (uint16_t) (servo_out * 1000));
    }
}

    // calculate_desired_throttle - uses throttle curve and collective input to determine throttle setting
float AP_MotorsHeli_RSC::calculate_desired_throttle(float collective_in)
{

    const float inpt = collective_in * 4.0f + 1.0f;
    uint8_t idx = constrain_int16(int8_t(collective_in * 4), 0, 3);
    const float a = inpt - (idx + 1.0f);
    const float b = (idx + 1.0f) - inpt + 1.0f;
    float throttle = _thrcrv_poly[idx][0] * a + _thrcrv_poly[idx][1] * b + _thrcrv_poly[idx][2] * (powf(a,3.0f) - a) / 6.0f + _thrcrv_poly[idx][3] * (powf(b,3.0f) - b) / 6.0f;

    throttle = constrain_float(throttle, 0.0f, 1.0f);
    return throttle;

}