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# Wheels rotating without any order given

Hello everyone, I know there are a lot of topics about this kind of problems but I read through a lot of them without getting an answer to my problem. So basically, I have a robot which is made of a base_link (collada file, but it's similar to a rectangle), 2 caster wheels to the front and 2 rotating wheels to the back. So what happens when I launch the simulation, the robot rotates around the Z axis without any cmd_vel being applied to the wheel or for or whatever. I'm really lost here guys so I request your help. I also add that when I turn on collisions view on Gazebo, it shows that every part of my robot is in collision, even with the self-collide turned on false, and the floor itslef is also in collision (it's the basic empty world). I join you my xacro file so that you may help me, and thanks everyone for reading to this point. I'm using Gazebo 7.0.

robot.xacro:

<?xml version='1.0'?>
<robot name="robot" xmlns:xacro="http://www.ros.org/wiki/xacro">
<!-- Put here the robot description -->

<xacro:include filename="$(find robot_description)/urdf/robot.gazebo" /> <xacro:include filename="$(find robot_description)/urdf/macros.xacro" />

<xacro:property name="PI" value="3.1415926535897931"/>

<xacro:property name="chassis_Height" value="0.002"/>
<xacro:property name="chassis_Length" value="0.310"/>
<xacro:property name="chassis_Width" value="0.240"/>
<xacro:property name="chassis_Mass" value="0.375"/>

<xacro:property name="casterRadius" value="0.0075"/>
<xacro:property name="casterMass" value="0.2"/>

<xacro:property name="wheelWidth" value="0.03175"/>
<xacro:property name="wheelRadius" value="0.03175"/>
<xacro:property name="wheelMass" value="0.2"/>

<link name="base_link"/>
<!-- Link chassis -->
<link name='chassis_link'>
<collision>
<origin xyz="0 0 0" rpy="0 0 0"/>
<geometry>
<mesh filename="package://robot_description/meshes/chassis_milieu.dae"/>
</geometry>
</collision>
<visual>
<origin xyz="0 0 0" rpy="0 0 0"/>
<geometry>
<mesh filename="package://robot_description/meshes/chassis_milieu.dae"/>
</geometry>
</visual>
<inertial>
<origin xyz="0 0 0" rpy="0 0 0"/>
<mass value="${chassis_Mass}"/> <origin xyz="0 0 0" rpy="0 0 0"/> <box_inertia m="${chassis_Mass}" x="${chassis_Length}" y="${chassis_Width}"           z="${chassis_Height}"/> </inertial> </link> <!-- Joint chassis sur base_link --> <joint name="base_joint" type="fixed"> <origin xyz="0 0 100" rpy="0 0 0"/> <!-- The 100 here was to make sure my robot isn't actually conflicting with the floor --> <parent link="base_link"/> <child link="chassis_link"/> </joint> <!-- Macro (link+joint) roues --> <wheel lr="left" tY="1"/> <wheel lr="right" tY="-1"/> <!-- Link roue libre gauche --> <link name="caster_wheel_left"> <collision> <origin xyz="0 0 0" rpy="0 0 0"/> <geometry> <sphere radius="${casterRadius}"/>
</geometry>
</collision>
<visual>
<origin xyz="0 0 0" rpy="0 0 0"/>
<geometry>
<sphere radius="${casterRadius}"/> </geometry> </visual> <inertial> <origin xyz="0 0 0" rpy="0 0 0"/> <mass value="${casterMass}"/>
<sphere_inertia m="${casterMass}" r="${casterRadius}"/>
</inertial>
</link>

<joint name="caster_wheel_left_joint" type="continuous">
<origin xyz="0.15 0.05 ${-casterRadius-chassis_Height/2}" rpy="0 0 0"/> <axis xyz="1 1 1" rpy="0 0 ... edit retag close merge delete ## 1 Answer Sort by » oldest newest most voted There are some things you can try to minimize the drift. 1) Increase the kp value of your wheels like so: <gazebo reference="${lr}_wheel">
<mu1 value="1.0"/>
<mu2 value="1.0"/>
<kp  value="10000000.0" />
<kd  value="1.0" />
<fdir1 value="1 0 0"/>
</gazebo>


This is the value I use and I get minimal drift. (though my robot is 4-wheeled)

2) Lower your robot's center of mass by lowering the body's intertia z position.

3) Increase real_time_update rate in your physics settings (while lowering max_step_size) if your computer can handle it.

Though because it is a vehicle with two casters some of the drift may be unavoidable considering one side of the robot is very easy to move.

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Asked: 2018-04-25 11:23:05 -0600

Seen: 165 times

Last updated: Apr 27 '18