Xacro like functionality in mujoco's xml #106

pab47 · 2022-01-11T04:39:37Z

pab47
Jan 11, 2022

Is there a way to define variables in XML and use them, much like how xacro's are used in urdf? For example, in urdf on can define the variable radius and then assign it to say 4.3. Something like this in urdf.
<xacro:property name="radius" value="4.3" />

saran-t · 2022-01-11T14:07:50Z

saran-t
Jan 11, 2022
Maintainer

MJCF doesn't support macros, however it does provide cascading <default> mechanism. This allows you to define classes of objects that share the same property (e.g. radius in your example). Please refer to the Defaults settings section in our documentation for further detail.

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brehman-hiab · 2022-01-19T07:41:50Z

brehman-hiab
Jan 19, 2022

Hello @saran-t
I am also looking for something similar, I tried using default but I am not able to understand how to do it correctly.
My objective is to spawn multiply instances of the robot given a different origins position, and also maintain only one or two files instead of writing one big XML.

For example, I wrote two XML files separately for two robots:

(file 1)-Mobile wheel robot (the free joint that can take a parameter to modify origin pos)
(file 2)-fixed based robotic arm (this file can take two parameters as an input to modify the default origin pos of the base link and parent body)

(file 3) then write another XML file that can use these two robot models
include mobile robot file
include based robotic arm file give pos as the new origin and parent body name

furthermore, write another file that can insert file3 to spawn multiply robot given a different origin

I know, name of the body, joints and actuator cannot be repeated for that I want to append name for example
body name="${name}_base"

I have written the first two files just for discussion
(file 1)

<mujoco model="mobilebase">
    <include file="baisc_scene.xml"/> 
    <compiler inertiafromgeom="true" angle ="degree"/> <!-- telling the we will use degree-->
    <option timestep ="0.001"/> <!-- Setting sample time as 1ms -->
    <worldbody>
        <body name="mobile_torso" pos="0 0 0.65" euler="0 0 0">
            <geom type="box" size="1 0.5 0.25 " rgba=".8 .2 .1 1"/>
            <freejoint name="root"/>
            <body name="right_FW" pos="0.5 -0.6 -0.1">
                <geom type="cylinder" size="0.25 0.1" rgba=".8 .2 .1 1" euler="90 0 0"/>
            </body>
            <body name="left_FW" pos="0.5 0.6 -0.1">
                <geom type="cylinder" size="0.25 0.1" rgba=".8 .2 .1 1" euler="90 0 0"/>
            </body>
            <body name="right_RW" pos="-0.5 -0.6 -0.1">
                <geom type="cylinder" size="0.25 0.1" rgba=".8 .2 .1 1" euler="90 0 0"/>
            </body>
            <body name="left_RW" pos="-0.5 0.6 -0.1">
                <geom type="cylinder" size="0.25 0.1" rgba=".8 .2 .1 1" euler="90 0 0"/>
            </body>
        </body>
    </worldbody>
</mujoco>

(file 2)

<mujoco model="robotarm">
    <include file="baisc_scene.xml"/> <!-- I am loading defult scene after removing a body that I dont need and can be orride as we want, file exist in same folder-->
    <compiler inertiafromgeom="true" angle ="degree"/> <!-- telling the we will use degree-->
    <option timestep ="0.001"/> <!-- Setting sample time as 1ms -->
    <worldbody>
        <body name="base" pos="0 0 0.0" euler="0 0 0">
            <geom type="cylinder" size="0.25 0.01" rgba=".8 .2 .1 1"/>           
            <body name="column" pos="0.0 0.0 0.0" euler="0 0 0">
                <geom type="capsule" size="0.035 0.25" pos="0 0 0.3" euler="0 0 0"/>
                
                    <body name="link1" pos="0.0 0.0 0.6" euler="90 0 0">
                        <geom type="capsule" size="0.035 0.25" pos="0 0 0.3" euler="0 0 0"/>
                        <joint name="pivot1" type="hinge" pos="0 0 0" axis="1 0 0" limited="false" damping="0.05"></joint>
                        
                            <body name="link2" pos="0.0 0.0 0.6" euler="0 0 0">
                                <geom type="capsule" size="0.035 0.25" pos="0 0 0.3" euler="0 0 0"/>
                                <joint name="pivot2" type="hinge" pos="0 0 0" axis="1 0 0" limited="false" damping="0.05"></joint>
                            </body>
                    </body>
            </body>
        </body>
    </worldbody>
        <actuator>
            <motor joint="pivot1" name="motor1" gear="1" forcelimited="true" forcerange="-100 100"/> <!--joint="pivot" is defined as hinge type in world body -->
            <motor joint="pivot2" name="motor" gear="1" forcelimited="true" forcerange="-100 100"/> <!--joint="pivot" is defined as hinge type in world body -->
        </actuator>
</mujoco>

0 replies

yuvaltassa · 2022-01-26T17:00:53Z

yuvaltassa
Jan 26, 2022
Maintainer

MuJoCo does not currently support model composition, other than the <include> clause which may or may not meet your needs.

While we are working to improve native model composition, your best bet is dm_control's mjcf module.

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Xacro like functionality in mujoco's xml #106

pab47 Jan 11, 2022

Replies: 3 comments

saran-t Jan 11, 2022 Maintainer

brehman-hiab Jan 19, 2022

yuvaltassa Jan 26, 2022 Maintainer

pab47
Jan 11, 2022

saran-t
Jan 11, 2022
Maintainer

brehman-hiab
Jan 19, 2022

yuvaltassa
Jan 26, 2022
Maintainer