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2018-11-28 10:42:00 -0500 asked a question Save robot in a given configuration not working

Save robot in a given configuration not working I am writing a model plugin to simulate a torque-controlled robot. I hav

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2017-01-30 02:57:08 -0500 commented question cant find inertial values from meshlab 1.3.3

If you are working in windows here there is the link for download: http://download.cnet.com/MeshLab-64-bit/3000-6677_4-75755741.html

2017-01-29 16:46:44 -0500 commented question cant find inertial values from meshlab 1.3.3

From your link seems there is a bug in the version you are using. Try the previous version 1.3.2, it is working fine.

2016-08-28 09:17:10 -0500 asked a question Publish matrix of arbitrary size over a gazebo topic

Hello everyone,

I am writing a gazebo model plugin that calculates and publishes as gazebo topic some quantities such as:

  • Joint space inertia matrix

  • Coriolis matrix

  • Jacobian matrix

  • Gravity vector

All these quantities are matrices whose size depends on the number of DoF of the considered robot model. I want to ask whether there is a way to publish an arbitrary sized matrix/vector over a gazebo topic without using custom messages.

Thanks for your help.

2016-08-26 00:03:10 -0500 commented answer Symbolic jacobian of an arm

Sure. My email address is: mar.selvaggio@gmail.com

2016-08-14 07:09:52 -0500 commented answer Symbolic jacobian of an arm

I would be happy to contribute to the writing of the KDL plugin

2016-07-04 09:14:06 -0500 answered a question How does ODE determine contact points in Gazebo?

According to the manual ODE approximates the contact between two bodies using a set of contact points. Given two geoms o1 and o2 that potentially intersect, the method dCollide generate these contact points and store them in an array then used to create contact joints. Depending on geoms type a different collision function is called. Usually the number of contact points as well as their order is determined within this latter function. For example in the case of box-plane collision dCollideBoxPlane method is called. It computes up to 4 collision points on the box and orders them based on their collision depth.

I suppose Atlas feet are approximately considered as boxes (check the feet collision meshes), that's why you get only 4 contact points. In ODE there is the possibility to create custom collision functions as callbacks, but I don't know how much effort is needed to change gazebo simulation code.

What you can easily do, instead, to get more collision points is to replace the collision meshes of Atlas feet with a more refined mesh made up by triangles (is easy to create one and export it in an STL file using Blender for instance).

Be careful since each extra contact point added to the simulation will slow it down, so sometimes we are forced to ignore contact points in the interests of speed.

Hope this can help.

2016-06-27 05:10:29 -0500 commented answer Simulation of pendulum not working as expected using ODE physics

I have no idea, but you can find the gazebo project status and the future release schedule here: http://gazebosim.org/

2016-06-27 03:59:34 -0500 commented answer How to add a color/material to a STL mesh in an URDF file?

I edited my answer. Check the new method.

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2016-06-25 10:06:59 -0500 answered a question How to add a color/material to a STL mesh in an URDF file?

You need to define the color separately such as in the file materials.xacro:

  <material name="Orange">
    <color rgba="${255/255} ${108/255} ${10/255} 1.0"/>
  </material>

Import materials.xacro in your file:

<xacro:include filename="$(find your_robot_description)/urdf/materials.xacro" />

Then you can use the color specifying a material tag for each link, such as:

<link name="$link_name">
  ...
  <visual>
     ...
    <material name="Orange"/>
  </visual>
  ...
</link>

For further information visit: http://gazebosim.org/tutorials/?tut=r...

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2016-06-18 08:23:12 -0500 answered a question Simulation of pendulum not working as expected using ODE physics

This is mainly a singularity problem since the body's moments of inertia are highly unequal and the inertia matrix is poorly conditioned. In this case, the integration error is very high resulting in unrealistic behaviour. This is particularly evident for long thin bodies rotating about their longer axis. For this reason, the user guide states that the user should avoid using long thin bodies.

In your case, by setting Izz=Ixx=Iyy the problem is solved and the natural period turns out to be approximately 0.7 seconds.

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2016-06-08 07:07:10 -0500 answered a question Symbolic jacobian of an arm

If you need the symbolic Jacobian of your robot you should calculate it in symbolic form using Matlab for example. It allows symbolic calculation as exemplified in this page. Moreover, the Matlab Robotic Toolbox has a C code generator useful to directly output the calculated symbolic quantities in C format.

On the other hand, KDL library allows you to numerically compute the matrices of the robot dynamic model (e.g. Inertia, Coriolis, Gravity) starting from robot state (joint positions, velocities). You can find the detailed implementation here.

Hope this can help.

2016-06-07 09:48:03 -0500 answered a question how to make a object static in gazebo

I never tried to do it through the gui, but you can easily specify those properties in the sdf file of the world you load, something like:

<model name='link'>
  <link name='link_name'>        
     <inertial>
      ...
      <mass>85</mass>
      ...
    </inertial>
  ...      
  </link>
  <static>1</static>
</model>

have look at this page to find out more about sdf specifications.

Hope this helps.