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Parallel Robots - Implementing close kinematic chains

asked 2014-10-27 13:44:33 -0500

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As I saw there is no official way for simulating close kinematic chains using URDF/SDF and gazebo.

2 questions:

  1. For a simple 4 arm mechanism: Will gazebo spawn an SDF with 4 Links and 4 joints forming this type of mechanism?
  2. If not, what is the right way of doing it?

Any direction would help.

Thanks

Nir

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Hi..i am a new user here. In my case several linear actuators are applying forces to the same joint in parallel - some of them spanning only one joint, some even two joints.As Gazebo7 features a graphical interface, is it possible to create those closed chains graphically?

NoellEagan gravatar imageNoellEagan ( 2017-10-12 13:31:45 -0500 )edit

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answered 2014-10-29 15:36:03 -0500

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This post is a wiki. Anyone with karma >75 is welcome to improve it.

Closed kinematic chains are not officially supported with URDF, though they are supported with SDF. Here is an example of an SDF model with closed chain. Also, the PR2 gripper has a 4-bar linkage.

We are planning to create a unit test for closed chains, but haven't done it yet.

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answered 2017-07-03 15:16:41 -0500

Duckfrost gravatar image

updated 2017-10-09 04:47:09 -0500

Building on what is already said, I created a Tutorial on Simple Closed Kinematics Model . Its just to have a starting point for anyone that is interested. It certainly helped me to understand it better and work afterwards on the fantastic tracksdriveplugin and my own projects .

image description

Here I leave you all the files I used, bith open and closed models sdf, their spawn launch files and the spawn sdf launch file:

simple_open_chain.sdf

open_chain_spawn.launch

simple_closed_chain.sdf

spawn_closekinem_example.launch

spawn_sdf_robotdesc.launch

You should be able to have something like this:

Hope this is usefull.

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answered 2016-02-04 09:32:49 -0500

sts gravatar image

Hi, I'm considering the same thing. In my case several linear actuators are applying forces to the same joint in parallel - some of them spanning only one joint, some even two joints.

As Gazebo7 features a graphical interface, is it possible to create those closed chains graphically? Are the physics engines able to calculate valid solutions?

Thanks!

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This sounds like a new question, not an answer. It would be nice if you could repost it as a question.

chapulina gravatar imagechapulina ( 2016-02-04 10:42:04 -0500 )edit
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Asked: 2014-10-27 13:44:33 -0500

Seen: 2,144 times

Last updated: Oct 09