Time delay for motor speed setting

[rohitdhak]

I am defining my subscribers and publishers as follows,

def start_ros_node(self):
        rospy.init_node('uav_controller', anonymous=True)
        # Motor control publisher
        self.motor_speed_publisher = rospy.Publisher('/hummingbird/command/motor_speed', Actuators, queue_size=10)
        # Quadcopter state subscribers
        self.imu_sub = message_filters.Subscriber('/hummingbird/ground_truth/imu', Imu)
        self.position_sub = message_filters.Subscriber('/hummingbird/ground_truth/position', PointStamped)
        self.odometry_sub = message_filters.Subscriber('/hummingbird/ground_truth/odometry', Odometry)
        self.motor_speed_sub = message_filters.Subscriber('/hummingbird/motor_speed', Actuators)

def sync_callback(self, imu_data, position_data, odometry_data, motor_speed_data):
        """Callback function to update internal state with synchronized data."""
        self.position = np.array([position_data.point.x, position_data.point.y, position_data.point.z])
        self.velocity = np.array([odometry_data.twist.twist.linear.x, odometry_data.twist.twist.linear.y, odometry_data.twist.twist.linear.z])
        self.motor_speeds = np.array(motor_speed_data.angular_velocities)  # Using the correct field
        self.orientation = np.array([imu_data.orientation.x, imu_data.orientation.y, imu_data.orientation.z, imu_data.orientation.w])
        self.angular_velocity = np.array([imu_data.angular_velocity.x, imu_data.angular_velocity.y, imu_data.angular_velocity.z])
        self.linear_acceleration = np.array([imu_data.linear_acceleration.x, imu_data.linear_acceleration.y, imu_data.linear_acceleration.z])

And I am setting motor speeds for hummingbird by publishing to Actuators

def publish_motor_speeds(self, motor_speeds):
        """Publish the motor speeds to the ROS topic."""
        motor_speed_msg = Actuators(angular_velocities=motor_speeds)
        self.motor_speed_publisher.publish(motor_speed_msg)

And in the main loop when I publish the motor speeds (self.motor_speed_publisher command) and then measure the motor speeds, its not the same. Mostly because the commands are not applied instantaneously.

In the hummingbird URDF file there is,

  <xacro:property name="time_constant_up" value="0.0125" /> <!-- [s] -->
  <xacro:property name="time_constant_down" value="0.025" /> <!-- [s] -->

Not sure exactly what these constants represents but even when I perform rospy.sleep(time_constant) I still dont get the commaned motor speeds.

How exactly the control are applied?
What is the exact ramp_up or ramp_down time for motors to reach the given setpoint?