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Which unit is Gazebo using when publishing to joint_states?

asked 2022-05-17 07:32:51 -0500

florian gravatar image

Hello.

I'm wondering which unit Gazebo is using when publishing to the topic joint_states. According to the message definition it could be (for the velocity) rad/s or m/s. I would appreciate any hint about that.

BR, Florian

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whats the type of joint ?

Fetullah Atas gravatar image Fetullah Atas  ( 2022-05-17 07:43:31 -0500 )edit

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answered 2022-05-17 07:54:49 -0500

ljaniec gravatar image

updated 2022-05-17 07:56:15 -0500

As per ROS REP 103: Standard Units of measure and Coordinate Conventions, units in Gazebo should be specified in meters and kilograms. (...)

https://www.ros.org/reps/rep-0103.html

It seems to depend on the controller:

http://wiki.ros.org/ros_control#Contr...

https://answers.gazebosim.org//questi...

and the joint type being controlled (http://wiki.ros.org/urdf/XML/joint):

<limit> (required only for revolute and prismatic joint)

An element can contain the following attributes:

  • lower (optional, defaults to 0)

An attribute specifying the lower joint limit (radians for revolute joints, meters for prismatic joints). Omit if joint is continuous.

  • upper (optional, defaults to 0)

An attribute specifying the upper joint limit (radians for revolute joints, meters for prismatic joints). Omit if joint is continuous.

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Thanks. In the model I am working with right now a JointVelocityController (http://wiki.ros.org/robot_mechanism_c...) is used. The type of the joint is 'continuous'.

florian gravatar image florian  ( 2022-05-19 01:53:26 -0500 )edit

Is the joint in the robot prismatic or revolute?

ljaniec gravatar image ljaniec  ( 2022-05-19 06:46:24 -0500 )edit

It's of type continuous.

florian gravatar image florian  ( 2022-05-20 05:49:59 -0500 )edit

What does it mean? Linear motion? Or rotational?

ljaniec gravatar image ljaniec  ( 2022-05-20 06:03:51 -0500 )edit

According to http://wiki.ros.org/urdf/XML/joint a continuous joint is defined as follows: a continuous hinge joint that rotates around the axis and has no upper and lower limits

Each wheel of the mobile robot has a joint of the mentioned type. It is used to apply linear velocity (in terms of revolutions per second).

florian gravatar image florian  ( 2022-05-20 06:57:29 -0500 )edit

Thank you for the clarification. It will be rad/s then

ljaniec gravatar image ljaniec  ( 2022-05-20 07:31:32 -0500 )edit

Thanks! =)

florian gravatar image florian  ( 2022-05-20 07:33:38 -0500 )edit

You may accept this answer so the question will be marked as solved

ljaniec gravatar image ljaniec  ( 2022-05-20 08:59:56 -0500 )edit

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Asked: 2022-05-17 07:32:51 -0500

Seen: 208 times

Last updated: May 17 '22