This questions is related to the previous thread: urdf-to-sdf-conversion [1].

Now, I'm reporting my observations when trying to use SDF tags from sdf1.4 in the URDF directly.

As mentioned in [1], it should be possible to use SDF within the gazebo tags referencing a link or joint within the URDF directly.

SDF tags for links

For setting most of the SDF tags relevant for links, URDF does not need the gazebo extensions, i.e. pose, ìnertial, visual and collision related tags are correctly set up using urdf-xml-link.

1. gravity and self_collide
   It's the same result as mentioned in this issue

2. kinematic
   It is converted to sdf. But seems to have no effect according to this thread

3. velocity_decay
   The following can be used to set velocity_decay of a link.
   With this, it's possible to set different values for linear and angular (in contrast to using the gazebo tag dampingFactor).

   <gazebo reference="${name}_base_link">
     <velocity_decay>
       <linear>0.2</linear>
       <angular>0.4</angular>
     </velocity_decay>
   </gazebo>
   

SDF tags for joints

Similar to the above mentioned, tags that can correctly be set up using urdf-xml-joint are not considered here.

1. damping and friction (dynamics)
   damping of an axis can only be set using the URDF tag dynmaics -> damping.
   All the following variants are not converted into the SDF file:

   <gazebo reference="${name}_1_joint">
     <axis>
       <dynamics>
         <damping>0.7</damping>
         <friction>0.7</friction>
       </dynamics>
     </axis>
     <dynamics>
       <damping>0.6</damping>
       <friction>0.6</friction>
     </dynamics>
     <damping>0.5</damping>
     <friction>0.5</friction> 
   </gazebo>
   

   friction cannot be set from anywhere as it is currently (not yet) supported (see PullRequest)

2. physics for ode (ode)
   Both following variants are not converted into the SDF file:

   <gazebo reference="${name}_1_joint">
   
     <provide_feedback>true</provide_feedback>
     <cfm_damping>true</cfm_damping>
     <fudge_factor>80</fudge_factor>
     <cfm>81</cfm>
     <erp>82</erp>
     <bounce>83</bounce>
     <max_force>84</max_force>
     <velocity>85</velocity>
     <limit>
       <cfm>86</cfm>
       <erp>87</erp>
     </limit>
     <suspension>
       <cfm>88</cfm>
       <erp>89</erp>
     </suspension>
   
     <physics>
       <ode>
         <provide_feedback>true</provide_feedback>
         <cfm_damping>true</cfm_damping>
         <fudge_factor>90</fudge_factor>
         <cfm>91</cfm>
         <erp>92</erp>
         <bounce>93</bounce>
         <max_force>94</max_force>
         <velocity>95</velocity>
         <limit>
           <cfm>96</cfm>
           <erp>97</erp>
         </limit>
         <suspension>
           <cfm>98</cfm>
           <erp>99</erp>
         </suspension>
       </ode>
     </physics>
   
   </gazebo>
   

Thus, it seems that using SDF tags directly within a URDF file is not supported - at least the way I tried to use them. In case I used them in the wrong way, please let me know! I'd be happy to test again then...

The only tags that are converted into the SDF file are gravity, self_collide (however, not considered due to issue), kinematic (however, see thread) and velocity_decay.

  <gazebo reference="link2">
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
  </gazebo>

>   <link name="wheel_f_l">
>     <collision name="collision">
>       <geometry>
>         <cylinder radius="${wheel_radius}"
>              length="${wheel_length}"/>
>       </geometry>
>     </collision>
>     <visual name="visual">
>       <geometry>
>         <cylinder radius="${wheel_radius}"
>           length="${wheel_length}"/>
>       </geometry>
>     </visual>
>     <xacro:solid_cylinder_inertial
>       radius="${wheel_radius}" height="${wheel_length}"
>       mass="${wheel_mass}" gcx="${0}" gcy="${0}" gcz="${0}"/>   
>     </link>

<gazebo reference="wheel_r_l">
        <mu1>100</mu1>
        <mu2>100</mu2>
        <maxContacts>1</maxContacts>
    </gazebo>