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Two Link Planar Robot (TLPR)


A ROS tutorial developed as part of ME495 - Embedded Systems in Robotics course in Northwestern University.

To launch (in a ROS workspace):

roslaunch two_link_planar_robot display.launch

May also launch using various parameters:

roslaunch two_link_planar_robot display.launch show_rviz:=True circle_length:=75 rate_update:=50 rate_animate:=20


To design a Two Link Planar Robot (TLPR) whose end effector traces and draws a circle

Project Objectives

  • Develop an URDF for TLPR
  • Use inverse kinematics to determine the joint angles given following trajectory:

  • Move the end effector by publishing sensor_msgs/JointState` message
  • Animate the trajectory by repeatedly using lookupTransform of tf.TransformListener and publishing a visualization_msgs/Marker to visualize path of the end effector

Package Contents

This ROS package contains the following files:

  • display.launch: A launch file to launch the following 2 nodes and a rviz configuration file (.rviz). The launch file also takes in below parameters:

    • frequency (rate) for publishing messages - two args: rate_joint:= and rate_animate:= (default=50 and =20 respectively)
    • adjustable time periods of circle drawn: circle_length:= (default=75)
    • option to show rviz: show_rviz:= (default=True)
  • node: This uses inverse kinematics to get the joint angles from the given trajectory and publishes the angles through joint_state_publisher to make the end effector move in circle [1]

  • node: This animates the trajectory and visualizes the path of end effector

TLPR gif

[1] Inverse kinematics formula adapted from