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cmd_vel and move_base

asked 2011-04-01 00:28:10 -0500

What are the conventions for the cmd_vel message produced by move_base? Is positive linear.x the forward or backward direction? Is positive angular.z clockwise or anti-clockwise as viewed from above?

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answered 2011-04-01 07:33:20 -0500

updated 2011-04-01 07:41:24 -0500

You have to think in the local frame of the robot. I'll dispense a couple of samples in the 2D-plane for ground robots:

Using the local robot base frame, the robot is always looking to the infinity of the x-axis (no matter where it located on the map). So if you command a Twist {linear.x=1,linear.y=0} the robot will go forward. You can see that if we are working with a non-holonomic robot (like the erratic robot) the linear.y has no meaning. In the other hand if you work with holonomic robot (like the PR2 base) the linear.y would mean lateral move.

The angular.z is the yaw rotation, that it's, the only possible rotation in the 2D plane where the robot stands (if we are talking about a ground robot in the plane). The angular.z veolocity is in radians and anti-clockwise. So a Twist message with angular.z > 0 means turn left in the local frame.

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answered 2011-04-01 02:22:19 -0500

arebgun gravatar image

Please see Standard Units of Measure and Coordinate Conventions page for a reference for the units and coordinate conventions used within ROS.

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Asked: 2011-04-01 00:28:10 -0500

Seen: 3,113 times

Last updated: Apr 01 '11