I dont understand how position can be chosen. Even if it is a rough guess i didnt get clear picture of it and also I didn’t understand rool, pitch, yaw positions for each parent link. Can you explain it a bit in an intuitive way.
Hi,
So in URDFS/XACROS you pasition an element in basically two ways that get combined if used both:
-
Is through the origin tag in the links elements. There you can position the visual/collision/inertia elements repect to the origin of that link. This is used to reposition meshes because their origin was not set properly or to set the inertia origin in a different place to change the phyisical behaviour.
-
When you use a joint to connect two links. Ths will position the child links reffered to the parents origin. This is where you can position the different parts of a robot, is like the assembly.
As for the Roll pitch and yaw, there are the angles with which you define the ORIENTATION of a LINK. Lets say if you want the arm part of a robot to be oriented forward when assembling it , here is where you have to work.
Roll : Is how many radians to rotate the link around the X axis of that same link.
Pitch: is how many radians you rotate the link around the Y axis of that same link
Yaw: is how many radians you rotate the link around the Z axis of that same link
These definitions can vary specially if the axis have been changed. But that’s the theory.
1 Like
Hi
can you help me please to understand how you choose the values of this code of Exercise 2.2 Unit 2 Mastering with Gazebo :
<collision>
<geometry>
<box size="2 1.3 0.4" />
</geometry>
</collision>
<visual>
<geometry>
<box size="2 1.3 0.4" />
</geometry>
<material name="DarkBlue">
<color rgba="0.2 0.2 0.4 1" />
</material>
</visual>
</link>
<!-- Joint - caster wheel -->
<joint name="joint_chassis_caster_wheel" type="fixed">
<origin rpy="0 0 0" xyz="0.8 0 -0.15" />
<child link="link_caster_wheel" />
<parent link="link_chassis" />
<joint_properties damping="1.0" friction="1.0" />
</joint>
<!-- Link - caster wheel -->
<link name="link_caster_wheel">
<inertial>
<mass value="1" />
<origin xyz="0 0 0" rpy="0 0 0" />
<inertia ixx="0.002526666666667" ixy="0" ixz="0" iyy="0.002526666666667" iyz="0" izz="0.005"/>
</inertial>
<!-- Caster wheel support -->
<collision>
<origin rpy="0 0 0" xyz="0 0 -0.03" />
<geometry>
<sphere radius="0.2" />
</geometry>
</collision>
<visual>
<origin rpy="0 0 0" xyz="0 0 -0.03" />
<geometry>
<sphere radius="0.2" />
</geometry>
<material name="DarkBlue">
<color rgba="0.2 0.2 0.4 1" />
</material>
</visual>
<!-- Caster wheel -->
<collision>
<origin rpy="0 0 0" xyz="0 0 -0.15" />
<geometry>
<sphere radius="0.10" />
</geometry>
</collision>
<visual>
<origin rpy="0 0 0" xyz="0 0 -0.15" />
<geometry>
<sphere radius="0.10" />
</geometry>
<material name="Grey">
<color rgba="0.6 0.6 0.6 1" />
</material>
</visual>
</link>
<!-- Joint - chassis / left wheel -->
<joint name="joint_chassis_left_wheel" type="continuous">
<origin rpy="0 0 0" xyz="-0.5 0.65 0" />
<child link="link_left_wheel" />
<parent link="link_chassis" />
<axis rpy="0 0 0" xyz="0 1 0" />
<limit effort="10000" velocity="1000" />
<joint_properties damping="1.0" friction="1.0" />
</joint>
<!-- Link - left wheel -->
<link name="link_left_wheel">
<inertial>
<mass value="1" />
<origin xyz="0 0 0" rpy="0 0 0" />
<inertia ixx="0.002526666666667" ixy="0" ixz="0" iyy="0.002526666666667" iyz="0" izz="0.005"/>
</inertial>
<!-- Tires -->
<collision>
<origin rpy="1.5707 0 0" xyz="0 0.18 0" />
<geometry>
<cylinder length="0.12" radius="0.4"/>
</geometry>
</collision>
<visual>
<origin rpy="1.5707 0 0" xyz="0 0.18 0" />
<geometry>
<cylinder length="0.12" radius="0.4"/>
</geometry>
<material name="Black">
<color rgba="0.1 0.1 0.1 1" />
</material>
</visual>
<!-- Axle -->
<collision>
<origin rpy="1.5707 0 0" xyz="0 0.06 0" />
<geometry>
<cylinder length="0.12" radius="0.08"/>
</geometry>
</collision>
<visual>
<origin rpy="1.5707 0 0" xyz="0 0.06 0" />
<geometry>
<cylinder length="0.12" radius="0.08"/>
</geometry>
<material name="Grey">
<color rgba="0.6 0.6 0.6 1" />
</material>
</visual>
<!-- Hubcap -->
<visual>
<origin rpy="1.5707 0 0" xyz="0 0.25 0" />
<geometry>
<box size="0.02 0.5 0.02" />
</geometry>
<material name="Grey">
<color rgba="0.6 0.6 0.6 1" />
</material>
</visual>
</link>
<!-- Joint - chassis / right wheel -->
<joint name="joint_chassis_right_wheel" type="continuous">
<origin rpy="0 0 0" xyz="-0.5 -0.65 0" />
<child link="link_right_wheel" />
<parent link="link_chassis" />
<axis rpy="0 0 0" xyz="0 1 0" />
<limit effort="10000" velocity="1000" />
<joint_properties damping="1.0" friction="1.0" />
</joint>
<!-- Link - right wheel -->
<link name="link_right_wheel">
<inertial>
<mass value="1" />
<origin xyz="0 0 0" rpy="0 0 0" />
<inertia ixx="0.002526666666667" ixy="0" ixz="0" iyy="0.002526666666667" iyz="0" izz="0.005"/>
</inertial>
<!-- Tires -->
<collision>
<origin rpy="1.5707 0 0" xyz="0 -0.18 0" />
<geometry>
<cylinder length="0.12" radius="0.4"/>
</geometry>
</collision>
<visual>
<origin rpy="1.5707 0 0" xyz="0 -0.18 0" />
<geometry>
<cylinder length="0.12" radius="0.4"/>
</geometry>
<material name="Black">
<color rgba="0.1 0.1 0.1 1" />
</material>
</visual>
<!-- Axle -->
<collision>
<origin rpy="1.5707 0 0" xyz="0 -0.06 0" />
<geometry>
<cylinder length="0.12" radius="0.08"/>
</geometry>
</collision>
<visual>
<origin rpy="1.5707 0 0" xyz="0 -0.06 0" />
<geometry>
<cylinder length="0.12" radius="0.08"/>
</geometry>
<material name="Grey">
<color rgba="0.6 0.6 0.6 1" />
</material>
</visual>
<!-- Hubcap -->
<visual>
<origin rpy="1.5707 0 0" xyz="0 -0.25 0" />
<geometry>
<box size="0.02 0.5 0.02" />
</geometry>
<material name="Grey">
<color rgba="0.6 0.6 0.6 1" />
</material>
</visual>
</link>