Hi NItin,<br>In the erratic_gazebo example, the velocity commands (cmd_vel ros topic) is interpreted by gazebo_ros_diffdrive node, which in turn sends velocity commands to position_iface_0 in the model.  You can try and write something similar to gazebo_ros_diffdrive for 4 wheel differential drive, controlling both position_iface_0 and position_iface_01 as you have defined it in your XML.  In addition, you will need to adjust mu1 and mu2 for the wheels to allow sufficient slip so the 4 wheeled differential drive can turn the robot.  Beware how the wheelSeparation and wheelDiameter parameters affects your velocity commands.<br>

hope this answers some of your questions.<br>John<br><br><div class="gmail_quote">On Thu, Sep 9, 2010 at 3:32 AM, Nitin Dhiman <span dir="ltr">&lt;<a href="mailto:nitinkdhiman@gmail.com">nitinkdhiman@gmail.com</a>&gt;</span> wrote:<br>

<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div>Hello Friends,</div><div>I am trying to use URDF to model a 4wheel differential drive vehicle. It is more like Pioneer 3AT. </div>

<div>Tutorials explains basics but I still had not understood some of topics. I have some queries.</div>
<div><br></div><div>1. How can one model differential drive behaviour in 4 wheel robot. I had tried modifying erratic.urdf.xacro for this purpose but without much results. I am attaching erratic.urdf.xacro.</div><div><br>


</div><div>2. Do one need to write some kind of new driver for such kind of vehicle. erratic model make use of p3d .</div><div><br></div><div>3.. in &lt;link&gt; tag, origin is defined w.r.t. which coordinate?</div><div>

<br>
</div><div>I have one doubt about stage as well which might be very silly :-) . Stage is 2D simulator. Do it treat environment and other entities as 3D and visulalize it as 2D?</div><div><br></div><div>Thank you</div><div>


NItin</div>
<br>_______________________________________________<br>
ros-users mailing list<br>
<a href="mailto:ros-users@code.ros.org">ros-users@code.ros.org</a><br>
<a href="https://code.ros.org/mailman/listinfo/ros-users" target="_blank">https://code.ros.org/mailman/listinfo/ros-users</a><br>
<br></blockquote></div><br>