I have a 4 wheeled differential drive robot, like the Pioneer 3-AT. There are only two motors, one for left wheels and one for right wheels.
I want to send velocity commands to the robot, I'm using ROS and the standard commands are: [linear_velocity, angular_velocity].
I need to convert them into left and right velocities, from literature if I had 2 wheels I should do this:
$v_l = linear_v - \omega * |r|$
$v_r = linear_v + \omega * |r|$
where |r| is the absolute value of the distance from the wheels to the robot "center".
How should I take into account that I have 4 wheels?