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How to deal with limit tag when joint limits are changeable (depended on other links) and not fixed?

asked 2017-01-10 04:43:03 -0600

jake123 gravatar image

updated 2017-01-11 02:59:22 -0600

My robot has not fixed joint limits. On every position is has a different joint limits other side it will hit parent/child link. Or it will go out of working area because I removed support links (closed loop) that are increasing max payload. What I think is to add an extra dummy link to parent/child link to make collision detection and prevent crashing. But i can't deal when it is going out of working area. Can I add a mathematic equation on limits?

If not I should add again support links (counterweights for payload), close the open loop, prevent collision with parent links and then it will never go out of working area.. but i find it too difficult to close the open loop. Is there any way to deal with it?

Update1:

Question: How to make support_link_2 follow a specific point/axe on link_3

Video of the custom robot: https://2.sendvid.com/7w3a2jp5.mp4

Structure:

Structure

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answered 2017-01-10 07:27:43 -0600

gvdhoorn gravatar image

I can write a more extensive answer later, but for now: no, there is no support for festooning joint limits anywhere in ROS. Not in URDF, SDF or any consumers of those formats (joint_state_publisher, robot_state_publisher or Gazebo). MoveIt! does also not support this.

The big assumption in almost everything that deals with robot kinematics and geometry is that the structure is defined once, loaded at application startup and does not change.

Perhaps if you can describe your robot better (diagram or picture), we can suggest alternatives / work-arounds.

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Note that I'm not saying it'd be impossible to add such support, but that is not what you are asking for, I believe.

gvdhoorn gravatar imagegvdhoorn ( 2017-01-10 07:28:56 -0600 )edit

Please take a look on video

jake123 gravatar imagejake123 ( 2017-01-10 07:39:44 -0600 )edit

You may want to take a look at mimic joints

jrgnicho gravatar imagejrgnicho ( 2017-01-12 10:05:22 -0600 )edit

I use mimic on joint 3 which is depended on joint 2, but using mimic joint on support_links i am not able to close the open loop.

jake123 gravatar imagejake123 ( 2017-01-12 17:48:23 -0600 )edit

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Asked: 2017-01-10 04:43:03 -0600

Seen: 78 times

Last updated: Jan 11 '17