Overview

This tutorial will explain how to drive simulated Atlas around as if it were a wheeled robot (i.e., without walking or balancing).

Setup

We assume that you've already done the installation step.

If you haven't done so, add the environment setup.sh files to your .bashrc.

echo 'source /usr/share/drcsim/setup.sh' >> ~/.bashrc
source ~/.bashrc

Background

Note that this tutorial does not use the walking controller. It simply spawns Atlas with position controllers enabled that keep it standing upright, as shown in the following image:

Note that in drcsim 4.x.x, the robot starts with a standing pose:

Note that all of the robot's joints, including the legs, are physically simulated and actively controlled.

So the simulated robot in this tutorial can't walk, but we still want to move it around in the world. Fortunately, the simulated robot accepts velocity commands via ROS to translate and rotate in the plane, as if it were a wheeled robot.

Moving Atlas

1. Start the simulator:

   VRC_CHEATS_ENABLED=1 roslaunch drcsim_gazebo atlas.launch
   

   Note: Setting the variable VRC_CHEATS_ENABLED=1 exposes several development aid topics including /atlas/cmd_vel, which are by default disabled for the VRC competition.

   The simulated robot is awaiting ROS Twist messages, which specify 6-D velocities, on the atlas/cmd_vel topic. Check that with rostopic:

   rostopic info atlas/cmd_vel
   

   You should see something like:

   Type: geometry_msgs/Twist
   Publishers: None
   Subscribers:
   
   
   
   /gazebo (http://osrf-Latitude-E6420:35339/)
   

You can publish ROS Twist messages from anywhere, including from the command line, using rostopic. First, let's see what's in a Twist message, using rosmsg:

rosmsg show Twist

You should see:

[geometry_msgs/Twist]:
geometry_msgs/Vector3 linear
  float64 x
  float64 y
  float64 z
geometry_msgs/Vector3 angular
  float64 x
  float64 y
  float64 z

It's a 6-D velocity: 3 linear velocities (X, Y, and Z) and 3 angular velocities (rotations about X, Y, Z, also called roll, pitch, and yaw). Our robot is constrained to move in the plane, so we only care about X, Y, and yaw (rotation about Z).

2. Place the robot in a stand position:

   rostopic pub --once /atlas/mode std_msgs/String "pid_stand"
   

3. Pin the robot for keeping its feet off the ground:

   rostopic pub --once /atlas/mode std_msgs/String "pinned"
   

4. Make the robot drive counter-clockwise in a circle:

   rostopic pub -r 10 atlas/cmd_vel geometry_msgs/Twist '{ linear: { x: 0.5, y: 0.0, z: 0.0 }, angular: { x: 0.0, y: 0.0, z: 0.5 } }'
   

Gazebo with drc robot drcsim4 from OSRF on Vimeo.

Every cmd_vel sent has a lifetime associated. By default, the velocity command is applied to Atlas for 0.1 seconds. After that, the robot will stop. If you look at the previous rostopic command that you typed, we included a -r 10 option argument to publish the same message at 10 Hz., to guarantee that the robot does not stop.

It's also possible to modify the value of the velocity command timeout:

1. By adding a new ROS parameter in the atlas.launch file:

   <param name="/atlas/cmd_vel_timeout" type="double" value="0.2"/>
   

2. By executing rosparam before launching drcsim:

   rosparam set /atlas/cmd_vel_timeout 0.2
   

You can verify the commands being sent with the command:

rostopic echo atlas/cmd_vel

To stop the robot, press CTRL-C to cancel the previous command.

From here, you're ready to write code that moves the robot around the world.