[ros-users] using ROS with a new 7-DOF arm hardware

Patrick Beeson beeson.p at gmail.com
Tue Jun 14 15:53:26 UTC 2011

Great.  I look froward to trying this out once it's released.

One or two quick questions that are not at all clear.   Will (in the new 
tool chain) my custom JointTrajectoryAction controller also need to be a 
pr2_controller in order to use my URDF model with Gazebo?  I was going 
to make a joint_trajectory_action_node that communicated directly with 
my hard in soft real-time to start.   This wasn't going to be a 
pr2_controller at all.   But I will want to be able to use the urdf 
model to control the arm in Gazebo.   My understanding is that right 
now, somewhere, something allows controllers to run in simulation 
instead of on the ethercat hardware.  I can't seem to find a good 
example that shows where exactly the line in drawn between sim and real, 
but it looks like the default Gazebo pr2 sim AND the pr2 arm hardware  
both use 
robot_mechanism_controllers/src/joint_trajectory_action_controller.cpp.   Examining 
that controller, I find it VERY difficult to understand how the 
low-level joint commands are being set (they seem to be copied into a 
RealTimeBox that is never intialized, so I don't know where they go from 
there).    So is the sim joint communication happening below this?  Do I 
need to do something special to talk to simulated joints in Gazebo 
versus on my hardware?  Another way of asking, if I write a 
joint_trajectory_action_controller to talk to my specific hardware, will 
I need to write another to talk to Gazebo?   And Do these need to be 

On 06/13/2011 01:59 PM, Gil Jones wrote:
> Hi Patrick,
> We are currently actively (as in right this second) developing a tool
> chain that assists users in configuring and building applications for
> arm navigation on novel platforms.  We're aiming to have all of this
> working reliably and in a documented fashion in time for the release
> of e-turtle later this summer.  In the meantime, if you are interested
> in being an alpha tester of this functionality I can send you a
> rosinstall file and tell you a bit about how the tool chain works -
> this should definitely be the fastest way to go from a urdf to solving
> kinematics and generating collision-free trajectories for your arm
> using our software.  This is with the usual caveats that things aren't
> quite ready for prime-time.
> To use this new functionality you'll need a urdf and your own
> joint_trajectory_action, but all the intermediate configuration and
> launch file generation should be done for you.  This also doesn't help
> configure any of our manipulation stacks - those will not be released
> at 1.0 in e-turtle.
> All the documentation, etc will be cleaned up in conjunction with the
> e-turtle release, and now that we're taking the plunge towards a 1.0
> release of major parts of the system things should be substantially
> more stable as of e-turtle.
> -Gil
> --
> E. Gil Jones (gjones at willowgarage.com)
> Research Engineer
> Willow Garage, Inc.
> 68 Willow Road
> Menlo Park, CA 94025
> 650.475.9772
> On Mon, Jun 13, 2011 at 11:36 AM, Patrick Beeson<beeson.p at gmail.com>  wrote:
>> I'm attempting to try and utilize novel, custom-made 7-DOF modular arm
>> hardware with ROS, and I'd like any help people are willing to provide
>> in starting from scratch with getting a new arm working in ROS.  I
>> have lots of familiarity with ROS, writing ROS drivers for perception
>> and navigation hardware, but, I'm not a manipulation or kinematics
>> expert, and I'm having difficulties understanding exactly what I do
>> and do not need to implement on my end to use the move_arm high level
>> package.
>> Having previously used the navigation stack, and other such stacks,  I
>> assumed that I would need some sort of driver that would subscribe to
>> some topic that would send joint positions or velocities based on
>> higher level kinematics planning given URDF models of the joints.
>> Instead, what I found was this tutorial:
>> http://www.ros.org/wiki/arm_navigation/Tutorials/Running%20arm%20navigation%20on%20non-PR2%20arm,
>> which seems to imply the need for writing my own kinematics plugin in
>> addition to my own joint trajectory execution node.  I can certainly
>> do this given some time; however, previous emails implied a
>> generic_kinematics package in unstable that would be useful, but after
>> searching through the Subversion repository, a generic_kinematics
>> package does not exist anywhere.
>> So, I'm going to start my creating a joint_trajectory_execution node
>> that has a a joint_trajectory_action interface and does soft-realtime
>> control of my joints behind the scenes.  What I need help determining
>> is if/where any generic kinematics packages exist or if I need to
>> write my own for my arm.  If I need to write my own, more details on
>> how to get this working with the other relevant modules would be
>> useful.  If a generic package exists, where is it?  How do I feed it
>> the model of my arm?  Also (tutorial step 5) there are lots of other
>> bits and pieces lying around that need to get tied together that
>> aren't well documented.  All in all, what I need is a better tutorial
>> that gives a much more simplified explanation as to what pieces are
>> needed, how they fit together (from move_arm down to hardware
>> interface), what parameters are definitely needed and which can be
>> ignored, etc.
>> Any help on this would be appreciated.  I'm sure I could figure all of
>> this out given enough time, but these days, time is not a great luxury
>> that I have, and part of the reason I use ROS is that it has been easy
>> to create, use, swap nodes, messages, topics with relative ease.  the
>> ARM documentation however is quite lacking and the large number of
>> motion planning, kinematics, controller, and action modules are not
>> well documented as to what is deprecated, how things fit together,
>> etc.
>> Thanks in advance,
>> Patrick
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