Start motor 1 by 1

ArduCopter Copter 3.6
1

hi all
I’m trying to start motors one by one before arming sequences
I try several ways
I added a step in AP_MotorsMultirors::output_logic
I stuffed this step between SHUT_DOWN and SPIN_WHEN_ARMED

case SPIN_1BY1:{
    // set limits flags
    limit.roll_pitch = true;
    limit.yaw = true;
    limit.throttle_lower = true;
    limit.throttle_upper = true;
    
    _spin_up_ratio = 1.0f;
    if (motorcnt>=AP_MOTORS_MAX_NUM_MOTORS)
        {
            hal.console->printf("[%d] to armed\n",now);
            _spool_mode = SPIN_WHEN_ARMED;
            lastcall=now;
            motorcnt=0;
        }
    else
        if(now-lastcall>=500)
            {
                int16_t motor_out;
                
                motor_out = 1200;//calc_spin_up_to_pwm();//get_pwm_output_min();
                hal.console->printf("[%d] motor %d set to %d enable=%d\n",now,motorcnt,
                                    motor_out,motor_enabled[motorcnt]);
                lastcall=now;
                if(motor_enabled[motorcnt])
                    rc_write(motorcnt, motor_out);
                motorcnt++;
            }
}
    break;

I tried to move it after SPIN_WHEN_ARM i tryed to change the value setted by rcwrite
nothing change the motor stays mute until it arrives at SPIN_WHEN_ARM
anybody can explain me a bit more where are realy setted the pwm channel i’m in multirotors frame
thank’s for any help