[ros-users] Joint controller manager

Mon Jan 28 15:41:41 UTC 2013

Adolpho,

This is great stuff!

I've also been working on an orocos-based controller manager that has a
similar interface to the ROS PR2 controller manager. The system I put
together a year ago is really rough around the edges and could be designed
much better, though. I was already planning on jumping into a rewrite and
it'd be great to brainstorm ideas and put together something that can be
used by the community.

One thing that I think the ros-orocos integration needs is better support
for actionlib for calling orocos operations over ROS.

Another thing that I'd like to ensure is that the controller infrastructure
integrates well with the gazebo simulator, either via plugins or just over
the gazebo ROS interfaces.

There's a lot more that I think we should talk about, maybe we should
create a ros-robot-control-sig?

best,
-jon

On Mon, Jan 28, 2013 at 10:04 AM, Adolfo Rodríguez Tsouroukdissian <
adolfo.rodriguez at pal-robotics.com> wrote:

> Hello ROS and Orocos users,
>
> This is a call for feedback. I'm currently working on a "joint controller
> manager", that is, a component that manages joint resources and exposes
> them to control. For those familiar with the pr2_controller_manager, this
> would provide similar functionality and interfaces, while relaxing some
> constraints to allow easy porting to different hardware platforms. Exposing
> hardware to control (and realtime control in particular) is still a big
> hurdle, and it would be very desirable to make this at least an order of
> magnitude easier. Once a minimal set of controller interfaces are made
> available for a given platform (eg. mobile base controller, spline
> interpolator, ...), a truckload of higher-level functionality becomes
> available.
>
> At the moment I have an existing in-house solution that from a ROS API
> point of view looks pretty much like a pr2_controller_manager, and a design
> of where I'd like things to go, which is attached to this message in pdf
> form. As a next step I was planning on setting up a public repo and port
> the existing design from Orocos 1.x to Orocos 2.x, which adds the
> expressivity needed to address the missing features. But before that, I'd
> like to make a pause and ask for some feedback.
>
> - Is there interest in giving this topic a dedicated discussion place,
> like a mailing list or a ROS special interest group?.
>
> - If you take a look at the attached design, please be critic about it.
> What would you add or remove?, what would you do differently?.
>
> - What can you not accomplish (or have had trouble accomplishing) with the
> tools you or your team have used so far?.
>
> Finally, I'd like to be aware of any active and similarly scoped
> initiative, so please let me know if you're working on the subject. Late
> last week I found out almost by chance about the yet undocumented
> ros_control [1] repository, which deferred the writing of this email a day
> so I could familiarize with it. Its scope is very much aligned with my
> current objectives, as it consists of a library offering functionality
> similar to that of the pr2_controller_manager that can be adapted to other
> robot platforms. I'm looking forward to sharing opinions and use cases with
> all interested parties, and if possible map interest overlaps to common
> code. Some questions that come to my mind after reviewing the code in [1]:
>
> - Is it possible to have a controller with multiple interfaces (eg. send
> position + velocity + effort commands)?.
>
> - If I understand correctly, interfaces are limited by design to position,
> velocity and effort, and adding a new one (fancy example: stiffness) is not
> possible, correct?.
>
> - Is it possible to chain controllers as in the attached figure
> (r_arm_follow_joint_traj + r_arm_pid_controller) from configuration files,
> ie. without writing code?.
>
> - Controllers running at lower frequency than the manager need to
> implement this by doing work only one out of every n cycles, as separate
> controller threads are not supported, correct?.
>
> - Is there any work on decoupling the more common "workhorse" controllers
> out of the pr2_controller_manager infrastructure (eg. a couple of mobile
> base implementations, the FollowJointTrtajectory action)?. I've already
> spent some time factoring out the spline splicing and interpolation code
> from the FollowJointTrtajectory action, and was planning on writing some
> unit tests on it. If not, I can also make this available once the cleanup
> is complete.
>
> That's it for now, thanks for reading.
>
> [1] https://github.com/willowgarage/ros_control
>
> --
> Adolfo Rodríguez Tsouroukdissian
> Senior robotics engineer
> adolfo.rodriguez at pal-robotics.com
> http://www.pal-robotics.com
>
> PAL ROBOTICS S.L
> c/ Pujades 77-79, 4º4ª
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-- 
Jonathan Bohren
PhD Student
Dynamical Systems and Control Laboratory
Laboratory for Computational Sensing and Robotics
The Johns Hopkins University

(707) 520-4736
jbo at jhu.edu
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