[ros-users] replicating pr2_arm_kinematics for 6-DOF arm

[David Feil-Seifer]

OK, fixed. It turned out that the problem was in the way goto_cart.cpp
was translating the point into the torso's frame. The attached version
fixes the problem.

On Tue, Jul 20, 2010 at 7:18 PM, Morgan Quigley
<mquigley at cs.stanford.edu> wrote:
> Hi Dave,
>
> I'm definitely not the right person to ask about KDL, but perhaps the
> experts lurking on this list can help you out. However, in general
> with IK systems when this happens, you might try to loosen the
> tolerance on the solution, and (more importantly) when debugging
> things, give it your exact current joint configuration as the IK
> starting point, and the exact forward-kinematic position as your
> target position. That way you know you aren't asking the solver to go
> through an infeasible region on its way to the solution(s). If that
> fails, then I would suspect the error is in your URDF, and that's
> where urdf_to_graphviz and rviz can help out:
>
> http://www.ros.org/wiki/urdf/Tutorials/Create%20your%20own%20urdf%20file
>
> HTH,
> Morgan
>
> p.s., also triple-check each argument you're passing into KDL, such as
> the length of all the joint vectors, etc. It's easy to make a typo and
> end up with a generic error message like this.
>
>
>
> On Tue, Jul 20, 2010 at 5:03 PM, David Feil-Seifer
> <david.feilseifer at gmail.com> wrote:
>> I finally gave this a try and it did not work for me. Here is a
>> rewritten version to get joint bound info from the URDF file and to
>> get joint names from the urdf description as well. I've attached a
>> revised version.
>>
>> I tried this on both the PR2 and the Bandit model, and I kept getting
>> and "ik solver fail" error. This would occur even if I gave the
>> robot's current end-effector position. Attached are two files, on is a
>> revised goto_cart.cpp and another is a file that sends a test message.
>> To run on the pr2 model in gazebo:
>>
>> ./goto_cart _root_name:="l_shoulder_pan_link" _tip_name:="l_wrist_roll_link"
>> ./cmd_ik
>>
>> Are you using a version of kdl newer than what is being used in
>> cturtle? Have I messed something up with updating your file?
>>
>> On Sat, Jul 17, 2010 at 11:37 AM, Morgan Quigley
>> <mquigley at cs.stanford.edu> wrote:
>>> Hi Dave,
>>>
>>> The Orocos KDL library is great. I just switched to it last week; my
>>> code is pretty ugly, but it's using the KDL::ChainIkSolverPos_NR_JL
>>> class, which has joint limits:
>>>
>>> http://stanford-ros-pkg.googlecode.com/svn/trunk/openarms/control/goto_cart.cpp
>>>
>>> The ik_tool() function is what you're after. You set the joint limits
>>> when you construct the ChainIkSolverPos_NR_JL object; search for
>>> "ik_solver_pos" in that .cpp file to see the exact syntax.
>>>
>>> (sorry about all the commented code... it's a work in progress)
>>>
>>> HTH,
>>> Morgan
>>>
>>>
>>> On Sat, Jul 17, 2010 at 10:43 AM, David Feil-Seifer
>>> <david.feilseifer at gmail.com> wrote:
>>>> I am trying to replicate the IK-functionality of pr2_arm_navigation
>>>> for our humanoid robot, Bandit. I have attached a xacro file for it's
>>>> arm. I have it rendering correctly, and am able to have it mimic the
>>>> movements of a real Bandit with joint_states_publisher and a
>>>> /joint_states message. I seem to have correctly ported
>>>> pr2_arm_ik_solver and pr2_arm_kinematics by simply changing all 7's to
>>>> 6's and changing the names of the root and tip links
>>>> (bandit_torso_link and left/right_hand_link). However, I'm having
>>>> trouble with pr2_arm_ik.cpp. Clearly, the math here was meant for a
>>>> 7-DOF arm, and I don't really know what algorithm is being used here,
>>>> so I'm having trouble translating that to a 6-DOF arm. I have figured
>>>> out that in the init function, that I needed to change the
>>>> link_offsets for the shoulder_upperarm_offset, elbow_wrist offset, and
>>>> upperarm_elbow_offset values. Those are now correct. I am just having
>>>> trouble making computeIKShoulderPan and computeIKShoulderRoll to a 6
>>>> joint arm. Can anyone give me some guidance on how to proceed?
>>>>
>>>> I did look at the KDL examples on their website, but they were pretty
>>>> vague about creating an IK solver with joint limits.
>>>>
>>>> Thanks for your help.
>>>> -Dave
>>>>
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>>>>
>>>>
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