Homework 2 README

Maintained by Sarah Ziselman for ME 495 Embedded Systems

Overview

This package is composed of two parts: Turtle Trajectories and Xacro ARM.

Part I: Turtle Trajectories

Overview

This part of the package makes a turtlebot travel in a figure-8 trajectory either in simulation or in real life. It utilizes a python package homework2 to calculate the trajectory and the corresponding cmd_vel commands. See doc/kinematics.pdf for PDF document containing the calculations used for the python package.

Nodes:

• trajectory - this node calculates the figure-8 trajectory and corresponding control commands to move the turtlebot.
• simodom - this node simulates the odometry of the turtlebot.

Usage

The figure_eight.launch file launches the following nodes: trajectory, simodom joint_state_publisher, robot_state_publisher, and rviz. Use the following command to launch the nodes to command the trajectory in the turtlesim_node node.

roslaunch homework2 figure_eight.launch mode:=sim

Use the following command to launch the nodes to command the trajectory in real life.

roslaunch homework2 figure_eight.launch mode:=real

Configuration

Once the figure_eight.launch file is launched, the turtle is in the paused state. In order to begin the figure-8 trajectory, open another terminal and use the following command:

rosservice call /resume

Use the following command to return the turtle to the paused state.

rosservice call /pause

Note that using the pause and resume service will not change the trajectory or reset the position of the turtle. The turtlesim_node will result in the following:

The turtle in rviz will result in the following:

Lastly, in real mode, the turtlebot will result in the following:

Part II: Xacro ARM

Overview

This part of the package contains a self-written Xacro URDF for a two link revolute joint arm. The robot arm is visualized in rviz and joint angles are calculated such that the end-effector follows a straight-line trajectory. Nodes:

• arm_traj - this node calculates the trajectory of the robot arm end-effector and uses inverse kinematics to solve for the corresponding joint states, which get published to the joint_state topic.
• arm_marker - this node draws markers in rviz at the end-effector position. When x is positive, the marker will be a periwinkle sphere. When x is negative, the marker will be a lavender cube. This node publishes at 1/10th the frequency that the arm_traj node publishes at.

Usage

The following command loads the robot_state_publisher node, the joint_state_publisher_gui node, and a configuration in Rviz that visualizes the robot arm.

roslaunch homework2 arm_basics.launch

Once launched, the following robot arm should appear in Rviz as seen in the photo below:

The following command loads all the nodes mentioned above in arm_basics.launch, the arm_traj node, and the arm_marker node. This launch file starts robot arm's trajectory and draws markers at the end-effector position.

roslaunch homework2 arm_marker.launch

Once launched, the robot arm should follow a straight-line trajectory at a constant y-value as seen in the gif below: