[ros-users] urdf joint mimic tag

Rosen Diankov rosen.diankov at gmail.com
Fri Jan 14 04:23:39 UTC 2011


Perhaps you would consider doing how COLLADA does it: allow the user
to specify an arbitrary MathML function.

We recently added this functionality in openrave 0.2.17, which has
allowed us to simulate all sorts of closed chain kinematics not
previously possible. For example, this tractor here has 8 joints
forming a 1 DOF closed chain:

http://openrave-users-list.185357.n3.nabble.com/attachment/2221527/0/bobcat.jpg

which requires a 6 degree polynomial to be solved by one of the mimic joints.

openrave uses the fparser library for this
(http://warp.povusers.org/FunctionParser/), which has minimal
dependencies. If you don't mind a bigger package, there is
MathMLSolver (http://sourceforge.net/projects/mathmlsolver/)

rosen,

2011/1/14 David Lu!! <davidvlu at gmail.com>:
> Which packages do you think might support it?
> Currently, joint_state_publisher has functionality that works like the mimic
> tag might, but through additional parameters, not the actual tag. If it was
> "officially" added to the URDF schema, I could easily add in support for
> it.
>
> On Fri, Jan 7, 2011 at 11:27 PM, John Hsu <johnhsu at willowgarage.com> wrote:
>>
>> Hi Mrinal,
>> The mimic tag is actually not officially supported.  It was used by
>> openrave only.  If it's a really useful feature, please file a feature
>> request ticket, and we can work on pushing it through to being supported
>> officially.
>> Thanks,
>> John
>>
>> On Fri, Jan 7, 2011 at 3:55 AM, Mrinal Kalakrishnan <mail at mrinal.net>
>> wrote:
>>>
>>> Hi,
>>>
>>> I could not find any documentation about the joint <mimic> tag in
>>> urdf. I use the tag in my own model and I can read the values using
>>> the urdf parser, but I just want to confirm the semantics of "offset"
>>> and "multiplier" - can I assume that the mimicked value =
>>> angle*multiplier + offset?
>>>
>>> Also, I'm curious as to which packages actually support the use of
>>> mimic joints. For example, the cturtle robot_state_publisher currently
>>> requires all joint angle values in its input, i.e., mimic joint angle
>>> values are not inferred. Is this something that will be supported in
>>> future, or is it just a temporary solution that will be deprecated
>>> with urdf 2.0?
>>>
>>> - Mrinal
>>> _______________________________________________
>>> ros-users mailing list
>>> ros-users at code.ros.org
>>> https://code.ros.org/mailman/listinfo/ros-users
>>
>>
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>
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