ROS Resources: Documentation | Support | Discussion Forum | Index | Service Status | Q&A
Ask Your Question

cmd_vel components

asked 2016-02-04 13:06:11 -0600

mayank_m gravatar image

In case of cmd_vel.linear.x what does the x_component of velocity signify. Is it the velocity in x_direction or in the direction the car is facing ? Even when I put the cmd_vel.linear.y to 0 its y-coordinate still changes.

edit retag flag offensive close merge delete

2 Answers

Sort by ยป oldest newest most voted

answered 2016-02-04 13:46:35 -0600

It depends a little bit on what context you are asking this question in. Different applications may use the geometry_msgs/Twist fields in different ways. Generally speaking though, the velocities components listed in the message are meant to be body velocities i.e. the instantaneous velocity of a rigid body expressed in a body-fixed frame. So in most mobile robot platforms that conform to REP 103 (turtlesim, turtlebot, PR2, etc.) the x-component is always the forward velocity of the robot as seen from the robot's point of view. If you set the x-velocity component to be positive, the robot starts driving forward. Depending on the orientation of the robot, it's coordinates relative to some other frame (e.g. /map, /world) may be changing in more than one component.

The y-velocity component is the velocity that the robot should be translating "sideways". In a holonomic base (youBot, PR2), this velocity is significant. In a nonholonomic base (turtlebot), this velocity is ignored because the robot cannot have any velocity component in this direction (in the body-fixed frame).

The z-rotation component is the angular velocity of the robot about it's body-fixed, upward, z-axis (how fast is the robot spinning).

edit flag offensive delete link more

answered 2016-02-04 16:21:27 -0600

tn0432 gravatar image

Hi! Let us know what kind of simulation and packages are you using? The changes in y -coordinate may be from the noise. Some simulation includes noise which makes vehicle moves although you do not command.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools



Asked: 2016-02-04 13:06:11 -0600

Seen: 585 times

Last updated: Feb 04 '16