Only released in EOL distros:   hydro indigo kinetic

Overview

Trep is a Python module for modeling articulated rigid body mechanical systems in generalized coordinates. Trep supports basic simulation but it is primarily designed to serve as a calculation engine for analysis and optimal control algorithms that require 1st and 2nd derivatives of the system’s dynamics.

Full documentation is available at http://nxr.northwestern.edu/trep.

ROS Tools

Trep currently provides two features for usage in ROS packages - A URDF import tool and an extended MidpointVI class.

URDF Import Tool

Trep can create a system model using certain tags from the URDF XML specification. The following tags are supported:

• Link - name
  • Inertial
    • origin
    • mass
    • inertia (only ixx,iyy,izz supported, off-axes should be zero)
• Joint - name, type: fixed, continuous, prismatic (no joint limits)
  • origin
  • parent
  • child
  • dynamics (damping only)

Additionally, one extra tag is supported on the Joint tag. Specifying kinematic='True' creates a kinematic configuration variable in trep for that joint.

An example of a system created from a URDF on the parameter server is:

   1 import rospy
   2 import trep.ros as rostrep
   3 
   4 system = rostrep.import_urdf(rospy.get_param('robot_description'))

Additionally, import_urdf can import the URDF onto an existing system definition and can add a prefix to all of the frames and joints created from the URDF using the following syntax:

   1 system = rostrep.import_urdf(rospy.get_param('robot_description'), 
   2          system=prev_system, prefix='new-prefix')

ROSMidpointVI Integrator

The ROSMidpointVI class extends the MidpointVI class available in trep. This class automatically publishes all frames imported from the URDF to the /tf topic every time ROSMidpointVI.step() is called.

Example Package

An example package called trep_urdf_demo is available at https://github.com/MurpheyLab/trep_urdf_demo. This package has two demos which can be called from launch files. After cloning the package to your ROS workspace, run the following command:

• RRbot simulator:

   roslaunch trep_urdf_demo rrbot.launch

• Interactive marionette simulator:

   roslaunch trep_urdf_demo puppet.launch