<div> </div>
<div> Morgan,</div>
<div> </div>
<div> Thanks, that is quite helpful. The point of my question was that I want to do this in a way which would make the arm as easy as possible for existing ROS users like, for example, those familiar with the PR-2 software, to just "drop in" my hand/arm. So I would not want to go create a buch of new messages and services and such if I could help it, I would like to figure out what level of abstraction is the correct place for my code to meet up with existing code. Is the "joint space controler" the place to do this? </div>
<div> If so, what exactly is the "joint space controler"? From what I read in the wiki, it looks like controlers are not exactly nodes, but some kind of module which is loaded into some general real-time layer which handles all controlers on the robot. Is that correct? (I am learning about ROS as I start this, so I appreciate your patience with what probably look like dumb questions.)</div>
<div> Really, what I am getting at is, if someone walked up to someone and said "hi, I made a cool hand, want to use it in your research?", what would be the best case for them, as ROS users, and possibly PR-2 owners, in terms of code I could have implemented to make the hand easy to use?</div>
<div> I gather that the Shadow Hand folks had this exact situation, what did they do?</div>
<div> </div>
<div>-=A</div>
<div> </div>
<div>ps. Nice to hear from you Morgan!<br><br></div>
<div class="gmail_quote">On Sun, Aug 1, 2010 at 11:10 PM, Morgan Quigley <span dir="ltr"><<a href="mailto:mquigley@cs.stanford.edu">mquigley@cs.stanford.edu</a>></span> wrote:<br>
<blockquote style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" class="gmail_quote">Hi Adrian,<br><br>I'm sure others will chime in here, but IMHO the greatest thing about<br>ROS is that you can do whatever you want :) it's designed from the<br>
ground up to be flexible and extensible, and to not favor one approach<br>over another equally-valid approach.<br><br>That being said, when I've built my own sensors and arms, if the<br>bandwidth isn't prohibitive, I first wrap up the hardware details in a<br>
ROS node that performs whatever bit-mashing is necessary to publish<br>and subscribe to abstracted versions of what the hardware deals with,<br>e.g., translating to/from some packet format that contains sensor<br>readings and actuator commands that goes over usb/ethernet/etc. to an<br>
embedded microcontroller. This node doesn't do anything beyond munging<br>the embedded protocol into ROS messages, and maybe do graceful<br>startup/shutdown of the hardware. When using the real hardware, this<br>program is started once during a session and left up for a few hours<br>
while hacking higher layers.<br><br>Once the driver wrapper is done, you can write higher layers that<br>either implement your own stuff or interface to other ROS software<br>(e.g., rviz, robot state publisher, nav stack, etc. etc.). Since those<br>
higher layers aren't tied to hardware, you can use rosbag to<br>record/play real data to the rest of the stack, and/or write a<br>simulation layer to swap with the "real" driver wrapper.<br><br>we just did a master-slave "puppeteer" demo of our arm that had a<br>
straightforward stack:<br><br>* human motion capture<br>* inverse kinematics via OROCOS/KDL<br>* robot state publisher (forward kinematics)<br>* joint-space controller<br>* state estimation from encoders, accelerometers, etc.<br>
* device driver wrappers<br><br>It's all available in an unvarnished state here:<br><a href="https://stanford-ros-pkg.googlecode.com/svn/trunk/openarms/" target="_blank">https://stanford-ros-pkg.googlecode.com/svn/trunk/openarms/</a><br>
<br>each layer is a separate node. All of them talk to rviz in one way or<br>another to ease debugging. The robot state publisher (from the WG<br>robot_model stack) converts joint angles and the robot's kinematic<br>description (URDF) into tf frames. When doing any of this stuff, rviz<br>
is extremely helpful when converting a new robot's cad models into<br>URDF and in general for making sense of all the coordinate systems.<br><br>HTH,<br><font color="#888888">-mq<br></font>
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<div class="h5"><br><br>On Sun, Aug 1, 2010 at 8:34 PM, Adrian <<a href="mailto:adrian.kaehler@gmail.com">adrian.kaehler@gmail.com</a>> wrote:<br>><br>> I am interested to know how one goes about creating an interface for<br>
> a device, such as an arm or hand. In particular, the question is what is<br>> the lowest level component in the ROS architecture which one would implement<br>> first? Presumably, once that low level element was in place, one could then<br>
> go on to create services or actions that make use of that component.<br>> Could someone point me to (or write?) a summary of what this stack looks<br>> like for something like the PR2 or Shadow arms?<br>><br>
><br></div></div>
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