Created new hardware interface for switching between controller modes

[davetcoleman]

This implements the "custom interface" described on this wiki page and addresses this issue #99

[davetcoleman]

@adolfo-rt could you review this?

[adolfo-rt]

I have seen this PR, but I can't really give an opinion yet, since I don't fully understand how the interface should be used (by controllers and the robot hardware abstraction) to change control modes at runtime (see comments on related ros_controllers PR).

So far I have the impression that static modes are well supported, but I'd like to know if the dynamic case should/will be supported, and how. I think this is a very good and attractive new feature, so we should take care that the most common usecases are well supported.

[davetcoleman]

The dynamic case is now supported. With my robot I can switch with these two calls:

switch to position mode

rosservice call /robot/controller_manager/switch_controller "{start_controllers: ['position_joint_mode_controller','left_position_trajectory_controller','right_position_trajectory_controller'], stop_controllers: ['velocity_joint_mode_controller','left_velocity_trajectory_controller','right_velocity_trajectory_controller'], strictness: 2}"

switch to velocity mode

rosservice call /robot/controller_manager/switch_controller "{start_controllers: ['velocity_joint_mode_controller','left_velocity_trajectory_controller','right_velocity_trajectory_controller'], stop_controllers: ['position_joint_mode_controller','left_position_trajectory_controller','right_position_trajectory_controller'], strictness: 2}"

[kphawkins]

So I'm not sure if I saw this when I wrote it, but I have an implementation which is very similar to this. I have a set of files strewn out over my gt-ros-pkg/universal_robot repository (hydro-devel-c-api branch) which perform a very similar function. They work natively with ros-control and do not require any direct modification, though more seamless integration would definitely help.

JointModeHandle
SwitchModeController
Implementations of SwitchModeController

In addition, I have a Python helper class which allows one to easily switch joint controllers without having to always keep up with current/new joint modes. This still needs work, but it is nice to only need to make a single call to the controller wanted running. I see no reason why ros-control can't automatically determine controller/joint mode conflicts and stop them properly.

URControllerManager
It requires that each controller be assigned a mode parameter, seen here.

I'm just leaving this here to help inform future discussion of a more official integration.

[adolfo-rt]

On these links:

JointModeHandle
SwitchModeController
Implementations of SwitchModeController

I like the fact that the handle type does not impose the available control modes, but is a general identifier (in your case an int). What is missing is a mapping between the identifiers and the actual hardware interfaces used by the controllers, which you are currently resolving with an additional mode setting in the controller configuration.

ros-controls/ros_controllers#62 has comments that are relevant to this discussion.

[fmessmer]

#180 is the rebased version for indigo-devel

[davetcoleman]

pal-robotics has been putting a lot of work into improving this original PR - I believe this PR has been superseded by the hydro-devel branch of https://github.com/pal-robotics/ros_control

@bmagyar can you confirm?

@ipa-fxm I think your rebased version should be closed in favor of pal-robotics work. @adolfo-rt can you confirm this?

[bmagyar]

I do confirm.