diff_drive_controller usage and operation

[fjp]

Hi, have some questions trying to use the diff_drive_controller from ros_control on a real differential drive robot. I try to measure the odometry with a simple lm393 speed sensor and an encoder disk with 20 slots.

1. The documentation states that diff_drive_controller works with wheel joints through a velocity interface. However, all the examples I've seen so far that implement a hardware_interface (slaterobotics, eborghi10/my_ROS_mobile_robot) read a position (angle) from the continuous wheel joints. Do I really need to provide the angle of the joints? I am asking because diff_drive_controller seems to use only a velocity interface and no position interface.
2. What's the range that I should put the angle in? [0, 2*pi[, [-pi, pi[ or something else? I am asking for a range because I found out that the angles get wrapped anyway according to this github issue

3. The example eborghi10/my_ROS_mobile_robot uses two yaml config files. One for the diff_drive_controller and another one that configures two effort_controllers. Why are the JointEffortController required for a differential drive robot? I thought that the diff_drive_controller should make the effort_controllers obsolete and it will have the diff-drive logic already implemented too.

How to implement the hardware_interface when the motors require a voltage value and the encoders provide encoder ticks as feedback?

[Bence Magyar]

I suggest you raise these questions on https://answers.ros.org/questions/ .

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