diff drive plugin has left and right backward

[gerkey]

I'm pretty sure that the diff drive plugin is getting the desired left and right wheel velocities backward when converting from vr and va. Here's the code:

wheel_speed_[LEFT] = vr + va * wheel_separation_ / 2.0;
wheel_speed_[RIGHT] = vr - va * wheel_separation_ / 2.0;

A positive va should induce counter-clockwise rotation, which requires the right wheel velocity to be larger than the left wheel velocity. With the above code, we'll get the opposite.

Anecdotal support for this being a bug is provided by the Gazebo tutorial example, in which the left and right joints are swapped, presumably in an effort to work around the problem.

[maxbader]

Hello Gerkey

Have a look at the pull request #272 this plug-in has multiple enhancements and the joints are defined as supposed.
Have a look on the multi_robot_scenario which can be launched out of the box.
gazebo_ros_pkgs/gazebo_plugins/test/multi_robot_scenario/xacro/p3dx/pioneer3dx_plugins.xacro

Greetings
Markus