Gripper choices?

[Patrick Goebel]

I know that Fergs has experimented with many gripper designs on Maxwell so this question is partly aimed at his experience but I hope others will join in.

I need a Dynamixel-compatible gripper for Pi Robot that would be suitable for playing with the new ROS MoveIt! pick and place.  I've always been impressed how well the PR2 does with its (apparently) simple pincer design.  This one from Trossen (which I think is Mike's design) looks like it might be a good start but I can't tell how wide it can open up.  There is also this one from Crustcrawler which has a much larger capacity but is not a parallel design.

Thoughts?

--patrick

[Michael Ferguson]

So Maxwell still has the "two servo gripper" kinda like the crustcrawler. I haven't gotten around to ever finishing the other pr2-style gripper I was working on. 

The small one from Trossen is very similar to the ones I was printing a while back. It will open up to 37mm (but if you want to open that much, the smallest you can close becomes 7mm) -- the 3rd picture in the product description shows the various configs based on how many foam pieces you install.

The PR2 gripper is quite a bit more complex than it looks. Effectively, each finger is a 4-bar linkage, and the two fingers are driven by the same motor through a 1:1 gearing between the joints. There are a lot of parts involved. The size is just about right, and also, you can use the "palm" area to support a workpiece.

As for Moveit -- I'm planning to actually drag Maxwell to this month's meeting, and demo the new Chess playing code (which you can also see at MakerFaire). My current code is availble here: https://github.com/mikeferguson/chessbox and https://github.com/mikeferguson/maxwell and includes a python interface to the pick and place pipeline in MoveIt.

-Fergs

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[Patrick Goebel]

Thanks Fergs--your Chess code will save me weeks or months of banging my
head against the wall. Interesting to hear how the PR2 gripper is
constructed. And yeah, I like the ability to use the side surfaces as a
"palm", something that is lacking in a lot of other pincer designs.
Looking forward to Maxwell's appearance at the Club meeting.

--patrick

[Patrick Goebel]

Hey Fergs,

So I  installed your Maxwell catkin packages and configured Pi Robot using MoveIt! I have everything working except I can't get past the following error during the launch of demo_fake.launch:

[FATAL] [1368577094.481407438]: Exception while loading controller manager 'simple_moveit_controller_manager/SimpleMoveItControllerManager': Could not find library corresponding to plugin simple_moveit_controller_manager/SimpleMoveItControllerManager. Make sure the plugin description XML file has the correct name of the library and that the library actually exists.

I've tweaked my $LD_LIBRARY_PATH variable to point to either ~/catkin_ws/devel/lib or ~/catkin_ws/install/lib depending on whether or not I run 'catkin_make install'.  What else am I missing to make sure your controller plugin can be found?

Thanks!
patrick

On 05/13/2013 11:13 PM, Michael Ferguson wrote:

...

[Michael Ferguson]

Are you sourcing devel/setup.bash? That's all you should need to do (I don't mess with LD_LIBRARY_PATH)...

-Fergs

[Patrick Goebel]

Yeah, I was doing that but because I am working in a mixed catkin/rosbuild enviroment, doing a 'source devel/setup.bash' blows away my ROS_PACKAGE_PATH (not sure why it doesn't just prepend to it).  I just now compared the output of printenv before and after 'source devel/setup.bash' and found that if I add the following lines to my .bashrc file, your plugin is found OK:

export LD_LIBRARY_PATH=~/catkin_ws/devel/lib:$LD_LIBRARY_PATH
export CATKIN_TEST_RESULTS_DIR=~/catkin_ws/build/test_results
export CPATH=~/catkin_ws/devel/include:$CPATH
export ROS_TEST_RESULTS_DIR=~/catkin_ws/build/test_results
export PATH=~/catkin_ws/devel/bin:$PATH
export PYTHONPATH=~/catkin_ws/devel/lib/python2.7/dist-packages:$PYTHONPATH
export PKG_CONFIG_PATH=~/catkin_ws/devel/lib/pkgconfig:$PKG_CONFIG_PATH
export CMAKE_PREFIX_PATH=~/catkin_ws/devel:$CMAKE_PREFIX_PATH

--patrick

[anfederman@comcast]

Hmm.... I followed the groovy environment set up instructions.   When I run the /ros_workspace/setup.bash  it calls the catkin_ws/devel/setup.bash and all packages can be seen.   I then can run either the ros_arduino_bridge or the Neato_node from the same groovy ros on either the Rpi or the ubuntu AMD-64.   Here are the wiki instructions:

 

http://ros.org/wiki/catkin/Tutorials/using_rosbuild_with_catkin

    go to section 3.3  rosbuild workspace on top of catkin workspace

[Patrick Goebel]

Hey Alan,

Thanks for the tip!  Seems I should read the instructions more carefully. ;-)  I'll give it a try.

--patrick