def get_motor_offsets(SERVO_OUTPUT_RAW, ofs, motor_ofs):
    '''calculate magnetic field strength from raw magnetometer'''
    import mavutil
    self = mavutil.mavfile_global

    m = SERVO_OUTPUT_RAW
    motor_pwm = m.servo1_raw + m.servo2_raw + m.servo3_raw + m.servo4_raw
    motor_pwm *= 0.25
    rc3_min = self.param('RC3_MIN', 1100)
    rc3_max = self.param('RC3_MAX', 1900)
    motor = (motor_pwm - rc3_min) / (rc3_max - rc3_min)
    if motor > 1.0:
        motor = 1.0
    if motor < 0.0:
        motor = 0.0

    motor_offsets0 = motor_ofs[0] * motor
    motor_offsets1 = motor_ofs[1] * motor
    motor_offsets2 = motor_ofs[2] * motor
    ofs = (ofs[0] + motor_offsets0, ofs[1] + motor_offsets1, ofs[2] + motor_offsets2)

    return ofs
calculate magnetic field strength from raw magnetometer