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how does KDL ChainDynParam and its JntToGravity actually work?

asked 2017-02-05 12:34:30 -0500

eugene.katsevman gravatar image

Hello! Could anyone share some tips and tricks? I've found that gravity should be 0, 0, -2 * 9.81 and this is strange. Another problem is that JntToGravity doesn't account for last chain link. I'm very confused with that and don't know where to look.

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KDL is actually not written / maintained by ROS / the OSRF, but is a library that is part of the OROCOS infrastructure. I think you'll have a better chance at getting good answers over at the KDL mailing list.

gvdhoorn gravatar imagegvdhoorn ( 2017-02-05 13:54:24 -0500 )edit

thanks. In a while, could you tell me if there is a KDL alternative inside of ROS?

eugene.katsevman gravatar imageeugene.katsevman ( 2017-02-05 14:05:55 -0500 )edit

For some of the minor functionality (frames, etc), perhaps Eigen could be an alternative. For all the other functionality (kinematics, solvers, dynamics, etc), there are probably alternatives, but I have none to recommend.

Note that KDL is very much used in ROS, just not developed / maintained.

gvdhoorn gravatar imagegvdhoorn ( 2017-02-06 02:53:59 -0500 )edit

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answered 2017-04-11 02:12:10 -0500

eugene.katsevman gravatar image

updated 2017-04-12 06:00:20 -0500

Ok, so there is a bug in kdl_parser_py. You have to specify xyz AND rpy for link origins, otherwise they're be set to 0 both, ruining your model.

UPD: Here is the link to the pull request, which fixes the bug:

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Thanks for reporting this. Have you opened an issue on a tracker somewhere? If so, could you include a link to that issue? That would help future readers find it.


gvdhoorn gravatar imagegvdhoorn ( 2017-04-11 11:50:17 -0500 )edit

Here is my pull request The discussion has stopped for whatever reason.

eugene.katsevman gravatar imageeugene.katsevman ( 2017-04-11 12:33:39 -0500 )edit

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Asked: 2017-02-05 12:34:30 -0500

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Last updated: Apr 12 '17