ardupilot/ArduCopter/crash_check.pde

/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-

// Code to detect a crash main ArduCopter code
#ifndef CRASH_CHECK_ITERATIONS_MAX
 # define CRASH_CHECK_ITERATIONS_MAX        20      // 2 second (ie. 10 iterations at 10hz) inverted indicates a crash
#endif
#ifndef CRASH_CHECK_ANGLE_DEVIATION_CD
 # define CRASH_CHECK_ANGLE_DEVIATION_CD    2000    // 20 degrees beyond angle max is signal we are inverted
#endif
#ifndef CRASH_CHECK_ALT_CHANGE_LIMIT_CM
 # define CRASH_CHECK_ALT_CHANGE_LIMIT_CM   50      // baro altitude must not change by more than 50cm
#endif

// crash_check - disarms motors if a crash has been detected
// crashes are detected by the vehicle being more than 20 degrees beyond it's angle limits continuously for more than 1 second
// should be called at 10hz
void crash_check()
{
    static uint8_t inverted_count;  // number of iterations we have been inverted
    static int32_t baro_alt_prev;

    // return immediately if motors are not armed or pilot's throttle is above zero
    if (!motors.armed() || (g.rc_3.control_in != 0 && !failsafe.radio)) {
        inverted_count = 0;
        return;
    }

    // return immediately if we are not in an angle stabilize flight mode or we are flipping
    if (control_mode == ACRO || control_mode == FLIP) {
        inverted_count = 0;
        return;
    }

    // check angles
    int32_t lean_max = aparm.angle_max + CRASH_CHECK_ANGLE_DEVIATION_CD;
    if (labs(ahrs.roll_sensor) > lean_max || labs(ahrs.pitch_sensor) > lean_max) {
        inverted_count++;

        // if we have just become inverted record the baro altitude
        if (inverted_count == 1) {
            baro_alt_prev = baro_alt;

        // exit if baro altitude change indicates we are moving (probably falling)
        }else if (labs(baro_alt - baro_alt_prev) > CRASH_CHECK_ALT_CHANGE_LIMIT_CM) {
            inverted_count = 0;
            return;

        // check if inverted for 2 seconds
        }else if (inverted_count >= CRASH_CHECK_ITERATIONS_MAX) {
            // log an error in the dataflash
            Log_Write_Error(ERROR_SUBSYSTEM_CRASH_CHECK, ERROR_CODE_CRASH_CHECK_CRASH);
            // send message to gcs
            gcs_send_text_P(SEVERITY_HIGH,PSTR("Crash: Disarming"));
            // disarm motors
            init_disarm_motors();
        }
    }else{
        // we are not inverted so reset counter
        inverted_count = 0;
    }
}