CS/ME/ECE/AE/BME 7785 Lab 4

CS/ME/ECE/AE/BME 7785
Lab 4

1 Overview
The objective of this lab is to design a set of controllers to make a robot drive through a set of way
points, given to you in a text file, in the presence of unknown obstacles. Figure 1 shows a cartoon
of the path that the robot will follow. The blue box is in a known stationary position within the
environment, while the purple object will be added by an instructor during the demo. The robot will
use onboard odometry and dead reckoning to determine its global position during the navigation.
It will be assumed that the robot starts at global position (0m, 0m) with orientation aligned with
the x-axis.
Figure 1: Cartoon of the experiment setup. The blue box is fixed in place while the purple faded
box will be placed by an instructor during the demo.
For this lab you can develop and test your code running roscore on your computer. However,
you must run roscore and all files on-board the robot for the demonstration. To move folders from
your computer to the robot, use the scp (secure copy) command. For example,
scp -r <Directory on your cpu to copy> burger@<ip-of-burger>:<Directory to copy to
on robot>
We strongly encourage you to use all available resources to complete this assignment. This
includes looking at the sample code provided with the robot, borrowing pieces of code from online
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tutorials, and talking to classmates. You may discuss solutions and problem solve with others in the
class, but this remains a team assignment and each team must submit their own solution. Multiple
teams can not jointly write the same program and each submit a copy, this will not be considered
a valid submission.
2 Lab Instructions
Create a package called TeamName_navigate_to_goal (refer back to the ROS tutorials from Lab
1 if needed). Useful dependencies include rospy, roscpp, sensor_msgs, std_msgs, nav_msgs, and
geometry_msgs. You can add as many nodes as you like. An example structure would be:
getObjectRange: This node should detect the ranges and orientation of obstacles. It should
subscribe to the scan node and publish the vector pointing from the robot to the nearest point on
the object.
Note: You will have to do some filtering of the LIDAR data to determine what measurements of
the 360 are useful. You may also want to segment your readings to be able to discern two obstacles
apart from one another. You will only encounter one obstacle at a time, but if your LIDAR sees the
wall or a stray chair/other robot you will want it’s object estimate to be robust. It is also important
to remember that this data is with respect to the robot’s local coordinate frame.
goToGoal: This node should subscribe to the odom node which determines the robots global
position from onboad sensors for you (using dead reckoning). It should also subscribe to the getObjectRange node to determine if there are any obstacles that need to be avoided.
This node should first read in the given goal locations from the wayPoints.txt file, or you can
include them in your code some other way. You should then create several controllers that drive
the robot through the sequence of given goal points without colliding with unknown obstacles. To
receive full credit the robot must stop for 10 seconds within a 10cm radius of the first goal point,
15cm radius of the second goal point, and 20cm radius of the third goal point, the robot must not
hit any obstacles, and the robot must reach the destination in under 2 minutes 30 seconds.
3 Possible Issues
1. Remember the onboard odometry and goal points are given in the same global frame while
the measurements are in the robot’s local frame. The package tf2 in ROS (http://wiki.ros.
org/tf2) may be useful to transform coordinate frames if you want but is not necessary for
this lab.
2. The Turtlebot3 has built in odometry which you are free to use. You can access it by subscribing to the /odom topic. It relies on proper calibration beforehand which can mess up if
you move the robot during its bringup. It is highly recommended to print out the robot’s
estimated pose to make sure the odometry is correct and not drifting while the robot is stationary. If you find it is messed up it can be fixed by placing the robot on the floor and
restarting the bringup.
3. The odometry node saves the current position of the robot and starts where it left off. If you
pick up the robot and restart your program to run the course, the odometry given to the robot
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will be the position and orientation the robot was last at before you picked it up. We have
given you a python script (RotationScript.py, to be released after Lab 2) which records the
initial odometry readings and subtracts them as an offset so your assumed starting position
is the origin with heading aligned with the x-axis. You may integrate this into your project
however you want.
4. The angular component of the odometry is represented by a quaternion which should be used
appropriately.
5. If you wish to create dead reckoning position updates yourself, or augment the ones produced
in the /odom topic, you can access the IMU and encoders through published topics /imu and
/sensor_state. More details can be found at http://wiki.ros.org/turtlebot3_bringup#Published_Topics.
4 Grading
You are allowed 5 attempts to demo this to an instructor and will receive the best score of your
attempts.
Run the code onboard the robot 25%
Drive within 10cm of the first goal point 25%(e
−
stopped_distance_outside_of_goal_in_cm
25 )
Drive within 15cm of the second goal point 25%(e
−
stopped_distance_outside_of_goal_in_cm
25 )
Drive within 20cm of the third goal point 25%(e
−
stopped_distance_outside_of_goal_in_cm
25 )
Each collision with an obstacle -5%
Take more than 2 minutes, 30 seconds to reach
the final goal point
-15%
Example grade:
You run all your code on the robot. Your robot reaches the first goal point within 10cm, hits the
obstacles once but makes it within 20 cm of the second goal point, and then reaches the final goal
point within 20cm. This is all done within 2 minutes, 30 seconds. Your grade would be...
grade = 25 − 5 + 25e
− 5
25 + 25 + 25
= 25 − 5 + 20.5 + 25 + 25
= 90.5
5 Submission
1. Perform a live demonstration of you running the robot to one of the course staff by the listed
deadline.
2. Put the names of both lab partners into the header of the python script. Put your python
script and any supplimentary files, in a single zip file called
Lab4_LastName1_LastName2.zip and upload on Canvas under Assignments–Lab 4.
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3. Only one of the partners needs to upload code.
We will set aside class time and office hours on the due date for these demos, but if your code is
ready ahead of time we encourage you to demo earlier in any of the office hours (you can then skip
class on the due date). Office hour times are listed on the Canvas homepage.
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