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Davide Picchi
Nov 17, 2014, 5:45:05 PM11/17/14
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Hi Patrick,
I've bought your second book and I find it very helpful.
Anyway it rises some questions, banal for you, but interesting for me :)
MoveIt expects for every robots a virtual_joint. And this is right what you did creating the virtual planar joint base_odom between /odom and /base_footprint frames.
But I was a little bit surprised and disoriented 3 or 4 pages later when I found out that this virtual_joint doesn't appear under the planning group definition, which indeed starts from /base_footprint
One could think: "yes..it's normal...this is for the robot arm"
Ok, clear, but what I don't understand is: how will be implemented the tf transformation of the virtual joint? Doesn't need the virtual joint a group with a planner?
Regards and keep going for the (future) 3rd book!!!
Bye
I've bought your second book and I find it very helpful.
Anyway it rises some questions, banal for you, but interesting for me :)
MoveIt expects for every robots a virtual_joint. And this is right what you did creating the virtual planar joint base_odom between /odom and /base_footprint frames.
But I was a little bit surprised and disoriented 3 or 4 pages later when I found out that this virtual_joint doesn't appear under the planning group definition, which indeed starts from /base_footprint
One could think: "yes..it's normal...this is for the robot arm"
Ok, clear, but what I don't understand is: how will be implemented the tf transformation of the virtual joint? Doesn't need the virtual joint a group with a planner?
Regards and keep going for the (future) 3rd book!!!
Bye
Patrick Goebel
Nov 18, 2014, 9:24:11 AM11/18/14
to ros-by-...@googlegroups.com
Hi Davide,
Good question! The base_odom virtual joint would be used in planning the motion of the whole robot if we wanted to do that. But as you noted, we are planning for the arm only. Note how the base_odom joint is defined as a planar joint which means it can move freely in any direction in the x-y plane. The only kind of ground-based robot that can move like that is one with an omnidirectional drive--i.e. a holonomic base like the PR2 has. MoveIt cannot currently plan the motion of a differential base which is non-holonomic. Instead, we use the ROS Navigation stack for that (e.g. move_base and the base_local_planner).
In summary, the virtual base_odom joint is included for completeness in our MoveIt setup, but we don't actually use it when planning the motion of a non-holonomic robot.
--patrick
Good question! The base_odom virtual joint would be used in planning the motion of the whole robot if we wanted to do that. But as you noted, we are planning for the arm only. Note how the base_odom joint is defined as a planar joint which means it can move freely in any direction in the x-y plane. The only kind of ground-based robot that can move like that is one with an omnidirectional drive--i.e. a holonomic base like the PR2 has. MoveIt cannot currently plan the motion of a differential base which is non-holonomic. Instead, we use the ROS Navigation stack for that (e.g. move_base and the base_local_planner).
In summary, the virtual base_odom joint is included for completeness in our MoveIt setup, but we don't actually use it when planning the motion of a non-holonomic robot.
--patrick
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