Autonomous Systems Assignment #1

EECS 195: Autonomous Systems 
Assignment #1

Problem 1: my_teleop_node (20 points)
In Lecture 2 we demonstrated how to use a ROS node named “turtlesim_teleop_key” to
control the turtle in the “turtlesim_node”. In this problem, you will write your own ROS node
named “my_teleop_node” that mimic the behavior of the “turtlesim_teleop_key” node.
Step 1: create a new workspace folder named LastName_FirstName_ws (replace LastName
and FirstName with your last and first name)
Step 2: create a package called “autoturtle” inside your workspace
Step 3: create a node (under the scripts folder) named “my_teleop_node”. This node should
do the following:
- Subscribe to the topic “/turtle1/cmd_vel”. This topic uses messages of the type
“geometry_msgs/Twist” which can be imported in your Python script using:
from geometry_msgs.msg import Twist
- Write Python code that takes input from the keyboard. Whenever the user hits the “w”
key, the turtle should move forward. Whenever the user hits the “s” key, the turtle should
move backwards. Whenever the user hits the key “a” then the turtle should rotate to the
left without moving. Finally, when the user hit the key “d” the turtle should rotate to the
right without moving. Below is a code snippet of how to create a message from type
Twist and fill in the important data fields.
move_cmd = Twist()
# Linear speed in x in units/second: positive values imply
# forward, negative values == backwards
move_cmd.linear.x = 0.3 # Modify this value to change the
# Turtle's speed
# Turn at 0.5 radians/s
move_cmd.angular.z = 0.5 # Modify this value to cause
rotation
# rad/s
Evaluation:
The grader is going to compile your code using catkin_make, source your setup.bash file,
then run your code using:
>> rosrun autoturtle my_teleop_node
It is your responsibility to make sure that no compilation errors will take place. Finally, the grader
will use the keys “w” “s” “a” “d” to move the turtle.
Problem 2: swim_node (30 points)
In this problem, you are required to create a new ROS node called swim_node. This node
should move the turtle in an “8 shape”.
Step 1: Create a new node in the same package autoturtle named swim_node under the
scripts folder.
Step 2: Upon initialization, this node should pick some random linear velocity and some
random angular velocity.
Step 3: The turtle then swims in a figure 8 shape using these random velocities.
Evaluation:
The grader is going to compile your code using catkin_make, source your setup.bash file,
then run your code using:
>> rosrun autoturtle swim_node
It is your responsibility to make sure that no compilation errors will take place. Once the node
starts, the turtle should continuously swim in a figure 8 shape.
Problem 3: swim_to_goal (50 points)
In this problem, you are required to create a new ROS node called swim_to_goal. This node
should take an input from the user specifying the target (x,y) coordinate of the goal. Your node
should then move the turtle to this (x,y) position.
Step 1: Create a new node in the same package autoturtle named swim_to_goal under
the scripts folder.
Step 2: Upon initialization, this node will ask the user to enter two numbers called x_goal and
y_goal
Step 3: Calculate the error between the turtle current position (current_x, current_y)
and the goal(x_goal,y_goal). Recall, the turtle pose can be retrieved by subscribing to
/turtle1/pose topic. This error can be computed as follows:
- Error_position = Euclidean distance between (current_x,
current_y) and (x_goal,y_goal)
- Error_angle = atan2(Error_position)
Step 4: Set the turtle velocity to be proportional to the error, i.e., when the turtle is far away from
the goal it should move faster than when the turtle is near the goal, and should not move when it
arrives to the goal. You can achieve this as follows:
- Linear_velocity = K_x * Error_position
- Angular_velocity = K_z * Error_angle
where K_x and K_z are some constants that you can choose. You may use
K_x = 1.5 and K_z = 4. Once you calculate the velocities, you can publish them on
the /turtle1/cmd_vel topic.
Step 5: Check if Error_position is smaller than 0.5, then you can stop moving the turtle.
Else, go to Step 3.
Step 6: When the turtle arrives to the final goal, it should ask the user for a new x_goal and
y_goaland then move the turtle accordingly.
Evaluation:
The grader is going to compile your code using catkin_make, source your setup.bash file,
then run your code using:
>> rosrun autoturtle swim_to_goal
It is your responsibility to make sure that no compilation errors will take place. Once the node
starts, the grader will ask the turtle to move to some random position. The grader will repeat this
process three times.
Deliverable:
- One zip file that contains your workspace and all the three ROS nodes.
- Ensure, the code you are submitting does not throw any errors during the
catkin_make. Otherwise, we won’t be able to grade your assignment.