ardupilot/ArduPlane/tiltrotor.cpp

#include "Plane.h"

/*
  control code for tiltrotors and tiltwings. Enabled by setting
  Q_TILT_MASK to a non-zero value
 */


/*
  calculate maximum tilt change as a proportion from 0 to 1 of tilt
 */
float QuadPlane::tilt_max_change(bool up)
{
    float rate;
    if (up || tilt.max_rate_down_dps <= 0) {
        rate = tilt.max_rate_up_dps;
    } else {
        rate = tilt.max_rate_down_dps;
    }
    if (tilt.tilt_type != TILT_TYPE_BINARY && !up) {
        bool fast_tilt = false;
        if (plane.control_mode == &plane.mode_manual) {
            fast_tilt = true;
        }
        if (hal.util->get_soft_armed() && !in_vtol_mode() && !assisted_flight) {
            fast_tilt = true;
        }
        if (fast_tilt) {
            // allow a minimum of 90 DPS in manual or if we are not
            // stabilising, to give fast control
            rate = MAX(rate, 90);
        }
    }
    return rate * plane.G_Dt / 90.0f;
}

/*
  output a slew limited tiltrotor angle. tilt is from 0 to 1
 */
void QuadPlane::tiltrotor_slew(float newtilt)
{
    float max_change = tilt_max_change(newtilt<tilt.current_tilt);
    tilt.current_tilt = constrain_float(newtilt, tilt.current_tilt-max_change, tilt.current_tilt+max_change);

    // translate to 0..1000 range and output
    SRV_Channels::set_output_scaled(SRV_Channel::k_motor_tilt, 1000 * tilt.current_tilt);
}

/*
  update motor tilt for continuous tilt servos
 */
void QuadPlane::tiltrotor_continuous_update(void)
{
    // default to inactive
    tilt.motors_active = false;

    // the maximum rate of throttle change
    float max_change;
    
    if (!in_vtol_mode() && (!hal.util->get_soft_armed() || !assisted_flight)) {
        // we are in pure fixed wing mode. Move the tiltable motors all the way forward and run them as
        // a forward motor
        tiltrotor_slew(1);

        max_change = tilt_max_change(false);
        
        float new_throttle = constrain_float(SRV_Channels::get_output_scaled(SRV_Channel::k_throttle)*0.01, 0, 1);
        if (tilt.current_tilt < 1) {
            tilt.current_throttle = constrain_float(new_throttle,
                                                    tilt.current_throttle-max_change,
                                                    tilt.current_throttle+max_change);
        } else {
            tilt.current_throttle = new_throttle;
        }
        if (!hal.util->get_soft_armed()) {
            tilt.current_throttle = 0;
        } else {
            // prevent motor shutdown
            tilt.motors_active = true;
        }
        if (!motor_test.running) {
            // the motors are all the way forward, start using them for fwd thrust
            uint8_t mask = is_zero(tilt.current_throttle)?0:(uint8_t)tilt.tilt_mask.get();
            motors->output_motor_mask(tilt.current_throttle, mask, plane.rudder_dt);
        }
        return;
    }

    // remember the throttle level we're using for VTOL flight
    float motors_throttle = motors->get_throttle();
    max_change = tilt_max_change(motors_throttle<tilt.current_throttle);
    tilt.current_throttle = constrain_float(motors_throttle,
                                            tilt.current_throttle-max_change,
                                            tilt.current_throttle+max_change);

    /*
      we are in a VTOL mode. We need to work out how much tilt is
      needed. There are 4 strategies we will use:

      1) without manual forward throttle control, the angle will be set to zero
         in QAUTOTUNE QACRO, QSTABILIZE and QHOVER. This
         enables these modes to be used as a safe recovery mode.

      2) with manual forward throttle control we will set the angle based on
         the demanded forward throttle via RC input.

      3) in fixed wing assisted flight or velocity controlled modes we
         will set the angle based on the demanded forward throttle,
         with a maximum tilt given by Q_TILT_MAX. This relies on
         Q_VFWD_GAIN being set.

      4) if we are in TRANSITION_TIMER mode then we are transitioning
         to forward flight and should put the rotors all the way forward
    */

    if (plane.control_mode == &plane.mode_qautotune) {
        tiltrotor_slew(0);
        return;
    }

    // if not in assisted flight and in QACRO, QSTABILIZE or QHOVER mode
    if (!assisted_flight &&
        (plane.control_mode == &plane.mode_qacro ||
         plane.control_mode == &plane.mode_qstabilize ||
         plane.control_mode == &plane.mode_qhover)) {
        if (rc_fwd_thr_ch == nullptr) {
            // no manual throttle control, set angle to zero
            tiltrotor_slew(0);
        } else {
            // manual control of forward throttle
            float settilt = .01f * forward_throttle_pct();
            tiltrotor_slew(settilt);
        }
        return;
    }

    if (assisted_flight &&
        transition_state >= TRANSITION_TIMER) {
        // we are transitioning to fixed wing - tilt the motors all
        // the way forward
        tiltrotor_slew(1);
    } else {
        // until we have completed the transition we limit the tilt to
        // Q_TILT_MAX. Anything above 50% throttle gets
        // Q_TILT_MAX. Below 50% throttle we decrease linearly. This
        // relies heavily on Q_VFWD_GAIN being set appropriately.
        float settilt = constrain_float(SRV_Channels::get_output_scaled(SRV_Channel::k_throttle) / 50.0f, 0, 1);
        tiltrotor_slew(settilt * tilt.max_angle_deg / 90.0f);
    }
}


/*
  output a slew limited tiltrotor angle. tilt is 0 or 1
 */
void QuadPlane::tiltrotor_binary_slew(bool forward)
{
    // The servo output is binary, not slew rate limited
    SRV_Channels::set_output_scaled(SRV_Channel::k_motor_tilt, forward?1000:0);

    // rate limiting current_tilt has the effect of delaying throttle in tiltrotor_binary_update
    float max_change = tilt_max_change(!forward);
    if (forward) {
        tilt.current_tilt = constrain_float(tilt.current_tilt+max_change, 0, 1);
    } else {
        tilt.current_tilt = constrain_float(tilt.current_tilt-max_change, 0, 1);
    }
}

/*
  update motor tilt for binary tilt servos
 */
void QuadPlane::tiltrotor_binary_update(void)
{
    // motors always active
    tilt.motors_active = true;

    if (!in_vtol_mode()) {
        // we are in pure fixed wing mode. Move the tiltable motors
        // all the way forward and run them as a forward motor
        tiltrotor_binary_slew(true);

        float new_throttle = SRV_Channels::get_output_scaled(SRV_Channel::k_throttle)*0.01f;
        if (tilt.current_tilt >= 1) {
            uint8_t mask = is_zero(new_throttle)?0:(uint8_t)tilt.tilt_mask.get();
            // the motors are all the way forward, start using them for fwd thrust
            motors->output_motor_mask(new_throttle, mask, plane.rudder_dt);
        }
    } else {
        tiltrotor_binary_slew(false);
    }
}


/*
  update motor tilt
 */
void QuadPlane::tiltrotor_update(void)
{
    if (tilt.tilt_mask <= 0) {
        // no motors to tilt
        return;
    }

    if (tilt.tilt_type == TILT_TYPE_BINARY) {
        tiltrotor_binary_update();
    } else {
        tiltrotor_continuous_update();
    }

    if (tilt.tilt_type == TILT_TYPE_VECTORED_YAW) {
        tiltrotor_vectored_yaw();
    }
}

/*
  tilt compensation for angle of tilt. When the rotors are tilted the
  roll effect of differential thrust on the tilted rotors is decreased
  and the yaw effect increased
  We have two factors we apply.

  1) when we are transitioning to fwd flight we scale the tilted rotors by 1/cos(angle). This pushes us towards more flight speed

  2) when we are transitioning to hover we scale the non-tilted rotors by cos(angle). This pushes us towards lower fwd thrust

  We also apply an equalisation to the tilted motors in proportion to
  how much tilt we have. This smoothly reduces the impact of the roll
  gains as we tilt further forward.

  For yaw, we apply differential thrust in proportion to the demanded
  yaw control and sin of the tilt angle

  Finally we ensure no requested thrust is over 1 by scaling back all
  motors so the largest thrust is at most 1.0
 */
void QuadPlane::tilt_compensate_angle(float *thrust, uint8_t num_motors, float non_tilted_mul, float tilted_mul)
{
    float tilt_total = 0;
    uint8_t tilt_count = 0;
    
    // apply tilt_factors first
    for (uint8_t i=0; i<num_motors; i++) {
        if (!is_motor_tilting(i)) {
            thrust[i] *= non_tilted_mul;
        } else {
            thrust[i] *= tilted_mul;
            tilt_total += thrust[i];
            tilt_count++;
        }
    }

    float largest_tilted = 0;
    const float sin_tilt = sinf(radians(tilt.current_tilt*90));
    // yaw_gain relates the amount of differential thrust we get from
    // tilt, so that the scaling of the yaw control is the same at any
    // tilt angle
    const float yaw_gain = sinf(radians(tilt.tilt_yaw_angle));
    const float avg_tilt_thrust = tilt_total / tilt_count;

    for (uint8_t i=0; i<num_motors; i++) {
        if (is_motor_tilting(i)) {
            // as we tilt we need to reduce the impact of the roll
            // controller. This simple method keeps the same average,
            // but moves us to no roll control as the angle increases
            thrust[i] = tilt.current_tilt * avg_tilt_thrust + thrust[i] * (1-tilt.current_tilt);
            // add in differential thrust for yaw control, scaled by tilt angle
            const float diff_thrust = motors->get_roll_factor(i) * motors->get_yaw() * sin_tilt * yaw_gain;
            thrust[i] += diff_thrust;
            largest_tilted = MAX(largest_tilted, thrust[i]);
        }
    }

    // if we are saturating one of the motors then reduce all motors
    // to keep them in proportion to the original thrust. This helps
    // maintain stability when tilted at a large angle
    if (largest_tilted > 1.0f) {
        float scale = 1.0f / largest_tilted;
        for (uint8_t i=0; i<num_motors; i++) {
            thrust[i] *= scale;
        }
    }
}

/*
  choose up or down tilt compensation based on flight mode When going
  to a fixed wing mode we use tilt_compensate_down, when going to a
  VTOL mode we use tilt_compensate_up
 */
void QuadPlane::tilt_compensate(float *thrust, uint8_t num_motors)
{
    if (tilt.current_tilt <= 0) {
        // the motors are not tilted, no compensation needed
        return;
    }
    if (in_vtol_mode()) {
        // we are transitioning to VTOL flight
        const float tilt_factor = cosf(radians(tilt.current_tilt*90));
        tilt_compensate_angle(thrust, num_motors, tilt_factor, 1);
    } else {
        float inv_tilt_factor;
        if (tilt.current_tilt > 0.98f) {
            inv_tilt_factor = 1.0 / cosf(radians(0.98f*90));
        } else {
            inv_tilt_factor = 1.0 / cosf(radians(tilt.current_tilt*90));
        }
        tilt_compensate_angle(thrust, num_motors, 1, inv_tilt_factor);
    }
}

/*
  return true if the rotors are fully tilted forward
 */
bool QuadPlane::tiltrotor_fully_fwd(void)
{
    if (tilt.tilt_mask <= 0) {
        return false;
    }
    return (tilt.current_tilt >= 1);
}

/*
  control vectored yaw with tilt multicopters
 */
void QuadPlane::tiltrotor_vectored_yaw(void)
{
    // total angle the tilt can go through
    float total_angle = 90 + tilt.tilt_yaw_angle;
    // output value (0 to 1) to get motors pointed straight up
    float zero_out = tilt.tilt_yaw_angle / total_angle;

    // calculate the basic tilt amount from current_tilt
    float base_output = zero_out + (tilt.current_tilt * (1 - zero_out));

    // for testing when disarmed, apply vectored yaw in proportion to rudder stick
    // Wait TILT_DELAY_MS after disarming to allow props to spin down first.
    constexpr uint32_t TILT_DELAY_MS = 3000;
    uint32_t now = AP_HAL::millis();
    if (!hal.util->get_soft_armed() && (plane.quadplane.options & OPTION_DISARMED_TILT)) {
        // this test is subject to wrapping at ~49 days, but the consequences are insignificant
        if ((now - hal.util->get_last_armed_change()) > TILT_DELAY_MS) {
            float yaw_out = plane.channel_rudder->get_control_in();
            yaw_out /= plane.channel_rudder->get_range();
            float yaw_range = zero_out;

            SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorLeft,  1000 * constrain_float(base_output + yaw_out * yaw_range,0,1));
            SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRight, 1000 * constrain_float(base_output - yaw_out * yaw_range,0,1));
            SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRear,  1000 * constrain_float(base_output,0,1));
            SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRearLeft,  1000 * constrain_float(base_output + yaw_out * yaw_range,0,1));
            SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRearRight, 1000 * constrain_float(base_output - yaw_out * yaw_range,0,1));
        }
        return;
    }

    float tilt_threshold = (tilt.max_angle_deg/90.0f);
    bool no_yaw = (tilt.current_tilt > tilt_threshold);
    if (no_yaw) {
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorLeft,  1000 * base_output);
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRight, 1000 * base_output);
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRear,  1000 * base_output);
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRearLeft,  1000 * base_output);
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRearRight, 1000 * base_output);
    } else {
        const float yaw_out = motors->get_yaw();
        const float roll_out = motors->get_roll();
        float yaw_range = zero_out;

        // now apply vectored thrust for yaw and roll.
        const float tilt_rad = radians(tilt.current_tilt*90);
        const float sin_tilt = sinf(tilt_rad);
        const float cos_tilt = cosf(tilt_rad);
        // the MotorsMatrix library normalises roll factor to 0.5, so
        // we need to use the same factor here to keep the same roll
        // gains when tilted as we have when not tilted
        const float avg_roll_factor = 0.5;
        const float tilt_offset = constrain_float(yaw_out * cos_tilt + avg_roll_factor * roll_out * sin_tilt, -1, 1);

        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorLeft,  1000 * constrain_float(base_output + tilt_offset * yaw_range,0,1));
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRight, 1000 * constrain_float(base_output - tilt_offset * yaw_range,0,1));
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRear,  1000 * constrain_float(base_output,0,1));
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRearLeft,  1000 * constrain_float(base_output + tilt_offset * yaw_range,0,1));
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRearRight, 1000 * constrain_float(base_output - tilt_offset * yaw_range,0,1));
    }
}

/*
  control bicopter tiltrotors
 */
void QuadPlane::tiltrotor_bicopter(void)
{
    if (tilt.tilt_type != TILT_TYPE_BICOPTER || motor_test.running) {
        // don't override motor test with motors_output
        return;
    }

    if (!in_vtol_mode() && tiltrotor_fully_fwd()) {
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorLeft,  -SERVO_MAX);
        SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRight, -SERVO_MAX);
        return;
    }

    float throttle = SRV_Channels::get_output_scaled(SRV_Channel::k_throttle);
    if (assisted_flight) {
        hold_stabilize(throttle * 0.01f);
        motors_output(true);
    } else {
        motors_output(false);
    }

    // bicopter assumes that trim is up so we scale down so match
    float tilt_left = SRV_Channels::get_output_scaled(SRV_Channel::k_tiltMotorLeft);
    float tilt_right = SRV_Channels::get_output_scaled(SRV_Channel::k_tiltMotorRight);

    if (is_negative(tilt_left)) {
        tilt_left *= tilt.tilt_yaw_angle / 90.0f;
    }
    if (is_negative(tilt_right)) {
        tilt_right *= tilt.tilt_yaw_angle / 90.0f;
    }

    // reduce authority of bicopter as motors are tilted forwards
    const float scaling = cosf(tilt.current_tilt * M_PI_2);
    tilt_left  *= scaling;
    tilt_right *= scaling;

    // add current tilt and constrain
    tilt_left  = constrain_float(-(tilt.current_tilt * SERVO_MAX) + tilt_left,  -SERVO_MAX, SERVO_MAX);
    tilt_right = constrain_float(-(tilt.current_tilt * SERVO_MAX) + tilt_right, -SERVO_MAX, SERVO_MAX);

    SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorLeft,  tilt_left);
    SRV_Channels::set_output_scaled(SRV_Channel::k_tiltMotorRight, tilt_right);
}