Hey Adolfo,<br><br>Thanks for this email. It brought out a good set of ideas on what we want from a controller framework. I will try and address your points with regards to [1] - the PR2 independent controller infrastructure that we have been developing. <br>
<br>The main goal of this work is to develop a robot-agnostic version of the PR2 controller infrastructure. In addition, we aim to develop a few (limited set of) controllers (based on the current set of controllers we have for the PR2) and release them as an open-source robot agnostic library. The controller manager and the controllers are intended to be usable with multiple realtime operating systems. A further part of this project is to take some of the workhorse capabilities performed by some of the controllers, e.g. the FollowJointTrajectory action and break them up into more sensible libraries (in addition to an actual controller implementation) that can be used across robots. <br>
<br>To answer some of your more direction questions:<br>- Is it possible to have a controller with multiple interfaces (eg. send position + velocity + effort commands)?.<br>yes, you will have to implement an interface that incorporates all these commands.<br>
- 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?.<br>Not true, you can implement other types of interfaces as well.<br>- 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?.<br>The follow joint trajectory controller will probably reuse the PID controllers (if that's what you are asking), but directly in code. I think I understand what you are referring to - we could design individual controllers to be more flexible so they can do something like this but its not something we have put much thought into yet.<br>
- 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?.<br>
The intention of this work is to provide a simple single-threaded infrastructure. We are probably going to stay away from anything more (e.g. multi-threading, etc.) mainly because there's other tools out there that will provide some of those capabilities for you.<br>
- 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.<br>
Yes. We probably won't do the mobile base though. <br><br>This is a joint project with a spin-off from Willow Garage: HiDOF Inc. (<a href="http://hidof.com" target="_blank">hidof.com</a>). As the project matures, more documentation will be added to make some of these things clearer. <br>
<br>Best Regards,<br>Sachin<br><br>
<br><div class="gmail_quote">On Mon, Jan 28, 2013 at 7:04 AM, Adolfo Rodríguez Tsouroukdissian <span dir="ltr"><<a href="mailto:adolfo.rodriguez@pal-robotics.com" target="_blank">adolfo.rodriguez@pal-robotics.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello ROS and Orocos users,<br><br>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.<br>
<br>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.<br>
<br>- Is there interest in giving this topic a dedicated discussion place, like a mailing list or a ROS special interest group?.<br><br>- 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?.<br>
<br>- What can you not accomplish (or have had trouble accomplishing) with the tools you or your team have used so far?.<br><br>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]:<br>
<br>- Is it possible to have a controller with multiple interfaces (eg. send position + velocity + effort commands)?.<br><br>- 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?.<br>
<br>- 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?.<br><br>- 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?.<br>
<br>- 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.<br>
<br>That's it for now, thanks for reading.<br><br>[1] <a href="https://github.com/willowgarage/ros_control" target="_blank">https://github.com/willowgarage/ros_control</a><br><br>-- <br>Adolfo Rodríguez Tsouroukdissian<br>
Senior robotics engineer<br>
<a href="mailto:adolfo.rodriguez@pal-robotics.com" target="_blank">adolfo.rodriguez@pal-robotics.com</a><br><a href="http://www.pal-robotics.com/" target="_blank">http://www.pal-robotics.com</a><br><br>PAL ROBOTICS S.L<br>
c/ Pujades 77-79, 4º4ª<br>08005 Barcelona, Spain.<br>Tel. <a href="tel:%2B34.93.414.53.47" value="+34934145347" target="_blank">+34.93.414.53.47</a><br>Fax.<a href="tel:%2B34.93.209.11.09" value="+34932091109" target="_blank">+34.93.209.11.09</a><br>
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<br></blockquote></div><br><br clear="all"><br>-- <br>Sachin Chitta<br>Manager and Research Scientist<br>Autonomous Mobile Manipulation Group<br>Willow Garage